_u.1ttI.J\Nl'ViBH1ImBAINB MALA¥IIIA

Laporan Akhir Projek PenyelidikanJangka Pendek

Effect of Alloying Elements on Propertiesof Aluminide-BaseJntermetallic MaterialDeveloped via Powder Metallurgy Route

byDr. Zuhailawati Hussain,

Assoc. Prof. Dr. Luay Bakir HussainAhmad Badri Ismail

f...

~ ,.

IlIfMUN1VE:RSITI SAINS MALAYSIA

FINAL REPORTOF

SHORT TERM RESEARCH GRANT

Title:

Effect Of Alloying Elements On Properties OfAluminide-Base Intermetallic Material Developed Via

Powder ~etallurgy Route

Account: 6035145

Duration: 15.4.2005-14.4.2007

Research Leader: Dr. Zuhailawati Hussain

Co-reseracher: Assoc. Prof. Dr. Luay Bakir HussainI

Mr. Ahmad Badri Ismail'"

School of Materials and Mineral Resources Engineering,Engineeri\i1g Campus,14300 Nibong Tebal,

Penange-mail: zuhaila@eng.usm.my

tel: 04-5995258 II

;1.d:j:\

Abstract

The present study deals with the effect of additive element on structure and properties

of Fe-Al intermetallic. FeAl-based intermetallic alloys with chromium or molybdenum

addition were fabricated by s intering of mechanically alloyed powders. The nominal

compositions of Fe-AI intermetallic alloys used in the present study were Fe-25AI, Fe-

24.375AI-2.5X, Fe-23.75AI-5X, Fe-23.l25AI-7.5X and Fe-22.5AI-lOX (X = Cr, Mo)

in wt% with the addition of 0.5% n-heptane and 0.5% zinc stearate. Bulk samples were

prepared by mechanical alloying in a planetary mill for 4 hours, pressing at 360 MPa

and sintering at 1000 DC for 2 hours. For compression tests, specimens were cut into

2mm x 2mm x 5 mm size and tested at room temperature using Instron machine. The

phase identification and microstructure of the consolidated material was examined by

x-ray diffraction and scanning electron microscope correspondingly. Density, hardness

~

and corrosion behaviour of the Fe-Ai based intermetallic alloy were studied as well.

Results showed that in compressive mode, the fracture strength and ductility of FeAICr2

sintered alloys increase with an increase in Cr composition due to solid solution

strengthening.. However, the addition of Mo more than 2.5wt% was accompanied by a

reduction in both properties due to the presence of Mo-rich precipitate particles in FeAI

microstructure which m'lY act as stress concentrator. Corrosion potential of Fe-AI-Cr

intermetallic aloy in 3.56wf!lVo NaCI solution was found to increase with increasing of

Cr content. These alloys exhibited typical passive behavior in NaCI solutions. SEM

observation of the corroded surface showed that the aluminides were subjected to

pitting corrosion in 3.56wt% NaCI media. It is revealed that the presence of chromiumi,

has enhanced passivation behavior of FeAhCr in NaCI solution.

1.0 Introduction

1.1 Literature Review

Intermetallic compounds have been the subject of scientific interest for more than 50

years because their attractive physical and mechanical properties. In recent years

research mostly focused on the use of monolithic intermetallic materials based on

aluminides as replacements for denser structural materials such as steels or superalloys

for high temperature service. Among the intermetallics, iron a1uminides are attractive

for elevated temperature applications due to their low density, low material cost and

good high temperature mechanical properties (Stoloff, 1998). In addition they exhibit

excellent corrosion resistance in oxidizing and sulphidizing atmospheres. Of the iron

aluminides, FeAI, has a B2 structure and exists over a wide range of Al concentrations

at room temperatures (36-50at%). Iron a1uminides based on FeAI exhibit better

oxidation resistance than Fe3AI alloys, have lower densities compared to the steels and~

commercial iron based alloys and exhibit higher electrical resistivity comparable to the

commercial metallic heating elements. These properties allow them to be considered as

high temperature structural materials, gas filters, heating elements, furnace fixtures,

heat-exchanger piping, catalytic converter substrates, automotive exhaust systems and

chemical production sys~m (Stoloff, 1998; Saigal et aI., 2003).

In recent years, there has been considerable interest in the synthesis and processing of

intermetallic compounds by means of mechanical alloying. Mechanical alloying (MA)

is a widely used process for synthesis of variety of alloys. The MA process leads to an.,alloy formation by solid state reactions assisted by severe plastic deformation that

occurs during ball milling of elemental powders. The MA technique allows one to

overcome problems such as, e.g., large difference in melting points of the alloying

1

2000).

temperatures. Recent research and development activities have demonstrated that

mechanical properties (Krasnowski and Kulik, 2006).

(eq.l),,2AI + 3HzO~ Ah03 + 6H

components a s well as unwanted segregation or evaporation t hat could occur during

melting and casting. Usually MA products possess nanocrystalline or amorphous

since the reduction of the grain size to nanometer scale can improve their physical and

adequate engineering ductility can be achieved in the aluminides through the control of

Iron aluminides were previously excluded from the realm of structural materials

because of their brittleness at ambient temperatures and poor strength at elevated

structure. Nanocrystalline materials are potentially attractive for many applications

microstructure and alloy additions (Stoloff et aI., 2000). Both tensile and creep

strengths of the aluminides are substantially improved by alloying with refractory

elements, which results in solution hardening and particle strengthening. The high-

temperature strength and fabricabili~ .of FeAI is improved by alloying this material

with molybdenum, carbon, chromium, and vanadium (Stollof, 1998; Stoloff et aI.,

Schneibel et. aI, (1996) has explained that the poor room temperature ductility of binary

iron aluminides is due to lheir susceptibility to hydrogen embrittlement (HE). This type

of embrittlement is thought t6 be due to the reduction of water vapor in the environment

surrounding the material via reactions such as:

and

Al + 2HzO~ AI(OH)z + 2H (eq.2)

2

Several methods have been proposed to minimize it like oxide coatings (to minimize

hydrogen pick-up from the environment), heat treatments (to produce a partially

recrystallized microstructure) and alloying with passivity-inducing elements (which

provide a passive layer on the surface 0 f the i ntermetallic that r educes the hydrogen

liberation rates on the surfaces and thereby minimizes hydrogen entry). The effects of

ternary additions, such as Ti, V, Cr, Mn, Ni, Nb, Mo, Ta, Cu and Si on room

temperatures ductility and strength have been extensively investigated. Even Cr

additions as low as 2% have been reported to be effective in providing improved

ductilities (Balasubramaniam, 1997; Huang et. aI, 1999)

Though, these materials are mainly developed for high temperature applications,

ambient temperature aqueous corrosi<:l.n;, can also be a serious problem for its durability.

This can happen when the alloys are possibly exposed to humid' environment

containing sulphates and/or chlorides, either during alloy processing stage or during

idling time of the finished components. Much of the previous research on the iron

aluminides focused on alloy development, processing and microstructral control and

improving mechanical pr6perties. Only a few investigations have reported to date the

corrosion behavior 0 f the irOn aluminide and its alloys. Extensive studies have been

published for oxidation, sulfidation and chloridation, whereas an aqueous corrosion

behavior has been less explored.

.,Investigations of mechanically alloyed FeAI intermetallic material have mostly

concentrated on synthesizing and thermodynamic studies of intermetallic powder.

Commercialization of FeAI has been limited due to the fabrication difficulty and poor

3

mechanical properties both at ambient and elevated temperature (Charlott et.al, 1999).

It is, therefore, important to develop ,optimized processing methods to utilize the

important attributes of intermetallic in developing high performance products. The

capability of converting finely divided intermetallic powders into useful, precise and

high engineering components efficiently and economically has prompted widespread

research in the field ofpowder metallurgy.

A systematic investigation has been conducted by the present authors to fabricate

tribological Fe-AI intermetallic alloys by a mechanical alloying approach, The main

goal of this study is to investigate the effect of chromium and molybdenum alloying

element on the microstructural and properties of FeAl. Cr was chosen as the ternary

alloying element because it has been reported that addition of Cr responsible for.-~

improving ductility, offering passivity, and add up to localized corrosion resistance.

While, Mo was chosen because other than improving mechanical properties, it also

gives beneficial effects on sulphidation resistance.

1.2 Objectives:

1. To characterize mec~nical properties and corrosion resistant of Fe-AI bulk material

which produced by powder"Compaction and sintering process.

2. To compare the effect of different alloying elements on the brittleness and corrosion

behavior of FeAI

·,

4

2.0 Research Methodology

Generally, research method in this project can be simplified as shown in Figure I.

n-heptanezinc stearate

Sintering in carbolite tube

Sample preparation

Sample Characterization:Compression test, hardness, density, XRD,r SEM. conosion test-----·-.r

Results & Analysis

Figure I: Flowchart of research ',-york

The nominal compositions of Fe-AI-Cr alloys used in the present study were Fe-25AI,I

Fe-24.375AI-2.5Cr, Fe-23.75AI-5Cr, Fe-23.125Al-7.5Cr aml..fe-22.5Al-l OCr (in wt%)"lC

with the addition of 0.5% n-heptane and 0.5% zinc stearate. While for Fe-AI-Mo

alloys, the investigated compositions were Fe-25AI, Fe-24.375AI-2.5Mo, Fe-23.75AI-

5Mo, Fe-23.125AI-7.5Mo, Fe-22.50AI-IO.OMo.

.,

Mechanical alloying of the mixture powder was carried out in a planetary mill for 4

hours. Consolidation of the mechanically alloyed powders was performed through cold

5

pressing under a pressure of 360 MPa followed by sintering at 1000 °C for a hold time

of2 hours. Sintering profile of the sample is shown in Figure 2.

Temperature,oC

Soakinl< time

1000

SOC /min

4Time, hour

6

SOC / min

10

Figure 2: Temperature profile for sintering of Fe-AI based intermetallic alloys.

Mechanical properties of the sintered ~ompacts were evaluated by compression test.

For compression tests, rectangular specimens with dimensions of 2 x 2 x 5 mm3 sizes

were sectioned from the compacts by diamond cutting. All surfaces of the specimens

were polished with SiC paper. These specimens were tested at room temperature using

Instron Machine. The structure of the sintered compacts was characterized by X-ray

diffraction (XRD). The s~ecimens was mechanically polished to 1!Jl11 grade diamond

powder and etched with 5% ~ital before observed under scanning electron microscope.

Density of the sample was measured using Archimedes method and hardness of the

sample was measured using Vickers microhardness tester.

,,

Before commencement of corrosion experiment, iron aluminides sample were mounted

using cold setting resin with one end soldered to a copper wire. Mounted specimens

were polished in a similar manner that was done for optical microscopy. These samples

6

were further rinsed with distilled water and methanol and dried. The anodic polarization

measurements were conducted at room temperature in 3.56wt%, NaCI solution.

Passivation behaviour and pitting resistance of iron aluminides were studied using

potentiodynamic polarization technique with a scan rate ofO.167mVis.

Figure 3: A set up for corrosion test using a potentiostat

The set-up consisted of a potentiostat driven by Gamry Instrument software and an

electrochemical corrosion~cell (Figure 3). The cell used for the polarization studies was

a beaker with 500ml capaci~, a graphite bar as counter electrode, a copper sulphate

electrode as a reference electrode and iron aluminides sample as a working electrode.

After corrosion test, specimen was rinsed with distilled water and dried. The sample

was observed under a scanning electron l11icroscopy (SEM) to examine the nature of,

corrosion.

7

3.0 Results and Discussion

This research is purposely to study the effect of chromium and molibdenum addition on

intermetallic Fe-AI behaviour prepared via mechanical alloying method. This research

involves milling process of ferum, aluminium and chromium/molibdenum powder

mixture powder, followed bye ompaction, s intering a nd characterization including x -

ray diffraction, microstructure, density, hardness, compression and corrosion tests.

Results and discussion for each analysis are given in the following subtopics.

3.1 X-ray Diffraction Analysis

X-ray diffraction analysis (XRD) was carried out on five samples of sintered Fe-AI

intermetallic which contains different percentage of chromium or molibdenum content.

The main objective to do x-ray diffraction analysis IS to identify the intermetallic

phases exists in the sample after sintering. ~

Figure 4 illustrates the diffraction patterns correspond tot he five samples consist of

different compositions of Fe-AI-Cr. The phase was identified by comparing the peak

positions and intensities with those listed in the Intenational Committee of Diffraction

Data (ICDD) files. Figure,4(a) of the X-ray diffraction patterns shown by FeAI mixture

sample is corresponding to t~ FeAI (pile Number: 33-20) and FeAh (File Number: 33-

19) phases but the intensity of FeAh peak is very low relative to FeAl.

Figure 4(b) to (e) illustrates the pattern from the Fe-AI mixtures with different amount\,

of Cr composition. For Cr containing FeAI mixtures, only single phase of Fe2AICr (File

Number: 42-1486) is detected. Another feature in the XRD pattern is that the peaks of

(220) approximately at 28=44° are shifted to lower angles with increasing Cr addition

8

which indicate that Cr present in solid solution in the alloyed intermetallics of Fe-Al-Cr

The atomic radius, r, of Fe, Al and Cr are 0.1241 run, 0.1431 nm and 0.1249 run

respectively. Therefore the decrease in lattice parameter of Fe2AlCr is due to the

replacement of larger Al atom by smaller Cr atom.

Figure 5 shows the diffraction pattern correspond to the five different Fe-Al-Mo

intermetallic alloys. Figures 5 (a) of the X-ray diffraction pattern shown by FeAI

mixture sample is corresponding to the FeAl (File Number: 33-0020). From FeAI

binary diagram the expected major phase to exist at composition of 25% Al with

sintering temperature of 1000°C is FeAl phase. From the ICDD file the lattice structure

of FeAI intermetallic compound is BCC structure.

~

Figure 5(b) to (e) shows the patteJ}ls from the FeAI with different amount of Mo

addition. For Mo containing Fe-AI mixtures, .single phase of FeAl (File Number: 33-

0020) is also detecteed. XRD studies indicate that the Mo present)n solid solution in

the alloyed intermetallics of Fe-AI-Mo. Ternary diagram of Fe-Al-Mo shows that for

the addition of Mo in range of 2.5-10% with sintering temperature of 1000°C, the

expected phase to exist ~l; FeAl.

•,

9

eo} r------------------_-----,

.- F~A1Cr

,

!I(d) Fe-24.3754\[::2.5Cr

(b) Fe-23.125AI-7.5Cr

(c) Fe-23.75AI~5CrFe2.A1Cr

II...IIiIlIlIL

Fe2.A1Cr"It

.Jl..

\ Fe2PJCr

Feitl

, v~(i l5 )).W j)

, , , , 1

" ~Iit; !'liE_"'_ ""·cJl'

Q lU ~-'l

,

FeAb

\ ...f ,

FeAI

\...A.

(e) Fe-25AI

\,

Fig. 4: XRD pattern of the Fe_AI-Cr intermetallic alloy with different compositions:

(a) Fe-22.50AI-IO.OCr, (b) Fe-23.125AI-7.5Cr, (c) Fe-23.75AI-5Cr, (d) Fe-24.375AI-

2.5Cr and (e) Fe-25A

10

(e) Fe-AI-IO%Mo

(a)Fe-25AI

(c) Fe-AI-5.0%Mo

..

'j

(d) Fe-23.125AI-7.5Mo and (e) Fe-22.50AI-1O.OMo.

iA -r '\ !If' "I "11t ," "F'r"'I"T,.t.,;1"'"1"" 'I'''''~ 1"t"'1"';'~"r' t 'f'1"T'~' 'i*'1""r'«Pl""/"'¥'~" eo 'HI '." I"t"' +1tJ i i j ,I i i 4· I i "I I" f i I I { i r r I

20 30 40 50 60 70 [°20] 80

,-

50

200 " ---------,-,-------------.,

150

100

[counts]

Fig. 5: XRD pattern ofthe Fe-AI-Mo intermetallic alloy with different compositions: (a) Fe-25AI, (b) Fe--24.375AI-2.5Mo, (c) Fe-23.75AI-5Mo,

11

3.2 Microstructure Observation

In this research, scanning electron microscope (SEM) was used to observe the

microstructure of sintered Fe-AI intermetallic compound with different content of

chromium/molibdenum. Fig.6 shows the observed microstructures for sintered Fe-AI-

Cr alloys with different Cr contents.

Fig.7 shows the observed microstructures for sintered Fe-AI-Mo alloys with different

Mo contents. White precipitates c an be observed mainly on the grain boundaries for

sample containing Mo. The amount of this precipitates obviously increases with

increasing Mo content. EDX analysis was perfonned to determine elemental

composition in the white precipitate (spot X) and the dark matrix (spot Y). Analysis on

spot X shows high content of Mo, followed by Fe and AI. While for spot Y, the major

element presence is Fe, followed l1y Al and Mo. C and 0 are also traced as

contamination. This results show that the white precipitate is Mo rich particle which is

not fully dissolved in the FeAl intennetallic phase.

,,

12

13

(a)

(b)I

Figure 6: SEM of sintered Fe-Al-Cr intermetaIIic alloy with different compositions:.,.(a) Fe-25AI (b) Fe-24.375AI-2.5Cr (c) Fe-23.75AI-5Cr (d) Fe-23.l25AI-7.5Cr

(d) FeAI-7.5Cr (e) FeAI-iOCr

,,

14

(c)

(d)

Figure 6 (continue)

.,

15

(e)

Figure 6 (continue)

,,

(a)

(b)

Figure 7 : SEM of sintered Fe-AI-Mo intermetallic alloy with different compositions:;

(a) Fe-25Al, (b) Fe-24.375AI-2.5Mo, (c) F;-23.75AI-5Mo, (d) Fe-23.125AI-7.5Mo and

(e) Fe-22.50AI-I0.0Mo.

16

17

(c)

•(d)

Figure 7 (continue)

18

(e)

Figure 7 (continue)

,,

c:l.edax32lgenesislgenmaps.spc 13-0et.200611:17:26LSecs: 28

1.8 Mo

1.4

OKAIKMoLFeK

10.9005.2253.7512.57

46.8521.8206.1917.9407.21

1.00 2.00 3:.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13:.0

c:1.edax32·o,genesis\genmal>s....pc 13-0et.-2006 11:20:28LSecs: 33

Element Wt% - :..4t% .

1.1CKOK

I 13.8501.50

36.8603.00

(b) 0.8 Fe

Kent

0.6

0.3: C

:..4IKMoLFeK

19.6201.4763.56

23.2500.4936.39

19

1.00 2.00 3:.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.0

Figure 8 EDX on a) spot X and b) spot Y in Figure 7e.

\,

3.3 Density Analysis

Archimedes method was carried out to measure density of intermetallic alloy bulk

sample. In this test, four samples were used for each composition to ensure data

consistency.

Figure 9 shows the green and sintered densities of Fe-Al-Cr intermetallic with different

amount of Cr. It is observed that the addition of Cr has increased the density by

eliminating pores in Fe-AI intermetallic compound.

4.8

...4.7

4.6 /~--- 4.5 /M

/'E~ 4.4 --~ -

I . IL .. i__ green density~

4.3

L I__ sintered densityIII 4.2l:: /(J)

£:) 4.1

l4

3.9 i3.8 I

0 2.5 5 7.5 70

Crcontent (%wt)

.1

Figure 9: Densities of gre~n and sintered body Fe-AI-Cr with different amount of Cr

Figure 10 is the average sintered density of Fe-AI-Mo intermetallic copmound with

different Mo composition. As shown in Rjgure 10, the sintered density increases when

the percentage of Mo has been increased. Sample with 10% mollbdenum shows the

highest density while sample with 2.5% molibdenum shows the lowest density.

20

4.25

4.2

4.15

l' 4.1(J

:§ 4.05

~ 4

j 3.95 J3.9 J

3.85

3.8

o 2.5 5 7.5 10Mo content (%wt)

Figure 10: Sintered density ofFe-AI-Cr with different amount ofMo

3.4 Mechanical Properties

In order to investigate mechanical prroperties of the Fe-AI-Cr and Fe-AI-Mo

intermetallic alooys, compression test were carried out. Each tesfwas repeated for three

different specimens from the same alloy. The compression test results for each of the

alloys were obtained fro~ the average of the three tests. The important results of the

compressive stress-strain CUf'l\!es of Fe-AI-Cr alloys are shown in Figure II and Figure

12.

Figure 11 shows the dependence of the compressive fracture stress (fracture strength),,

of FeAl alloys on the presence of Cr alloying elements. The increased fracture strentgh

of FeAl with 2.5-10% of Cr is most likely attributed to solid solution strentghening of

Cr as confirmed by XRD analysis. Solid solution strentghening occurs when the

21

dislocation mobility in a solid is restricted by the introduction of solute atoms (Husni,

2005). The presences of Cr solute atoms in FeAI alloys introduce discrete barriers

which restrict the motion ofthe dislocation glide that would lead to strengthening.

300

ro250c..

~J::+-' 200Clc:~

+-'VI 150Q)

>'00VI 100Q)L-a.E0 50U

O-l-

0 2.5 5 7.5 10

Cr content (%wt)

Fig. 10: Compressive strength of the Fe-AI-Cr intermetallic

Alloying with Cr also produces a higher strain compared to the base intermetallic which

indicates the improvement in ductility (Figure 12). The ductility results of the presentI

study are in agreement to earlier report where it was shown that Cr additions provide a'\C

passive layer on the surface of the intermetallic (Balasubramaniam, 2002). He has

explained the effect of Cr addition on embritlement of FeAI by mixed potential

analysis. He concluded that the rate of hydrogen liberation on the passivated surface of,

the Cr-alloyed iron aluminide is much lower than that surface of the binary aluminide.

Addition of higher content of Cr is beneficial to increase ductility by inducing thicker

passive film which delay hydrogen entry into FeAI alloys. Therefore, ductility is

improved because hydrogen embritlement of iron aluminides has been minimized.

22

0.09

0.08

0.07

0.06

c 0.05.~

(j) .0.04

0.03

0.02

0.01

0

0 2.5 5

Cr content (%wt)

7.5 10

Fig. 12: Strain of the Fe-AI-Cr intermetallic..

The important results of the compressive stress-strain curves of Fe-AI-Mo alloys are

shown in Figure 13 and Figure 14. As reported by (Sun et. ai, 1995), Mo are fOund to

be effective in strenthening aluminides through solid solution effect. On the other hand,

room temperature ductili~ decreases with addition of this element. However, in the

present work it was found "'that the addition of 2.5% Mo has given the result that

compressive strength and compressive strain are the highest value.

The decrease in compressive strength in the present work probably is due to the•,

presence of Mo-rich precipitates in Fe-AI-Mo intermetallic. As discusses previously by

(Banerjee and Balasubramaniam, 1998), these precipitates can be assumed as the 'flaw' .

which act as stress concentrators, thereby becoming the sources of premature failure.

23

When stress is applied, crack tends to first initiate around the precipitates, then grows,

and propagate leading to fracture. It can be said that after the onset of the plastic

deformation, due to the presence of more stress concentrators, the applied stress for Fe-

AI-5.0%Mo, Fe-AI-7.5%Mo and Fe-AI-10.O%Mo is lower than Fe-AI-2.5%Mo.

o 5 10

Fig. 13: Compressive strength ofthe Fe-AI-Mo intermetallic

0.07

0.00

t:: 0.05.~

....~ 0.04>'iii~ 0.03a.E<3 0.02

0.01

0

a 2.5 5

Mo content (o/<Wt)

7.5 10

24

Fig. 14: Strain of the Fe-AI-Mo intermetallic

3.5 Corrosion Test

Potentiodynamic polarization curves of all the four Fe-Al-Cr alloys and Fe-AI binary

are presented in Figure 15. These Fe-Al-Cr alloys exhibit a broad passive-pitting

behavior. The potentiodinamic polarization curve shows the passive-pitting behavior of

Fe-Al-Cr in 3.56wt% NaCI media. The electrochemical kinetic parameters which

determine the passive behavior of these alloys namely are corrosion potential, Ecorn

passive current density (ipassive) which is equal to corrosion current density, and pitting

potential Epitt) are derived from the curves. Polarization curves in Figure 15 shows that

the addition of Cr tends to slightly increase the passive pitting breakdown potential of

the alloys and thus slightly increases pitting. resistance of the alloy.

After the corrosion test, the samples were observed under SEM in order to study the

"nature of corrosion behavior 0 f t he ~luminides in NaCI media. Fig. 2 shows that all

samples are preferentially attacked by pitting corrosion after they are polarized higher

than their pitting potentials. In addition, it may naturally OGcuron passive metal or

alloys due to passive film breakdown at p otential ~ Epitt 0 r due to mechanical action

which can damage the passive film at potential < Epitt. Pitting corrosion is initiated at

locations at which the phssive film is weaker than other areas due to less Cr content.

Results also confirm that al(fminides without Cr addition are more susceptible to pitting

corrosion compared to other aluminides with the Cr addition.

I,

25

F~..~5.A1

..6..8..10

F~ ..~~.5Al .. l o:.a-

~

~12

~

/.•...........

....: -.-..................•...........c.~.:..it. . . Jt ...23.1251.1·1.50: // "~J1SAl.2.s0:

)\..23.15&1.. 5Cr

~~.

u.~

~.......,...r:r.l--r.fA1'0.~

,L·og i(AI

Figure 15: Potentiodynamic polarization curves ofFe-AI-Cr in 3.56wt% NaCI media

26

Figure 16: SEM image of aluminides after polarization showing pitting attack

(a) Fe-25AI (b) Fe-24.375AI-2.5Cr (c) Fe-2,3.75AI-5Cr (d) Fe-23.125AI-7.5Cr (e) Fe-,

22.5AI-I0Cr

27

4.0 Conclusion

1. XRD results shows that with composition of Fe-25w%tAI and sintering

temperature of lOOO°C, high intensity peak of FeAI phase observed. Low intensity

peak of FeAlz is detected as well indicating that this phase exist with minor inor

ferum aluminide intermetallic compound which is FeAI. This results suggest that

intermetallic compound produced contains FeAI as major phase and FeAl2 as

minor phase.

2. For Fe-AI-Cr mixtures, a single phase of Fe2AICr is detected. When more Cr

content is added, a decrease in the lattice parameter value of Fe2AICr occurs

indicating that Cr atom substitutes Al atom in Fe2AICr crystal structure.

3. For Fe-AI-Mo mixtures, a single phase of FeAI is observed in XRD pattern which

suggest that Mo exist as substitutional atom in FeAI solid solution.

4. Room temperature ductility of iron al~minide can be enhanced by the addition of.passivity-inducing element of Cr to the base iron aluminide. Cr exists in solid

solution in the iron aluminide which provide additional fracture strength to the base

metal.

5. Results show that 2.5wt%Mo addition significantly increased the ultimate stress

and ultimate strain in ~ompressive mode due to solid solution hardening. However,

addition of Mo more tha~ 2.5wt% is associated with a reduction in both properties

caused by the presence of Mo-rich precipitate particles.

6. Potentiodynamic polarization of iron aluminides in NaCI media shows the Fe-AI-

Cr are susceptible to pitting corrosioq. The pitting corrosion resistance and the,

passivation potential range of Fe-AI-Cr alloys increases with increasing of Cr

content.

28

5.0 References

1. Balasubramaniam R., (1997), Alloy development to minimize room temperature

hydrogen embrittlement in iron aluminides, Journal of Alloys and Compounds, Vol.

253-254, p 148-151.

2. Balasubramaniam R., (2002), Hydrogen in iron aluminides, Journal of Alloys and

Compounds, Vol. 330-332, p 506-510.

3. Banerjee P. and Balasubramaniam, R. Sripta Materialia, Vo1.38, No 7, pp.1l43-

1147,1998

4. Charlott, F., Gaffet, E. Bernard, F. and Niepce, J.e. (1999) Mechanically activated

synthesis studied by X-ray diffraction in the Fe-AI system. Materials Science and

Engineering. A262, 279-288

5. Huang YD., Yang W.Y and Sun Z.Q., (1999), Improvement of room temperature

tensile properties for Fe3Al-based alloys by thennomechanical and annealing

processes. Materials Science and Engineering, Vol. A263, p 75-84.

6. Husni U., Development of y-TiAl-based alloy produced by hot -pressing and arc.melting routes. 2005, MSc Thesis, Uriiversiti Sains Malaysia. pp75-79

7. Krasnowski M. and Kulik T., (2006), Nanocrystalline FeAl intennetallic produced

by mechanical alloying followed by hot-pressing consolidation, Intennetallics, p 1-

5.

8. Saigal, A. and Yang, W. Analysis of milling of iron aluminides. Journal of

Materials Processing Technology. 132,2003, 149-156

"9. Schneibel lH., George E.P. and Anderson I.M., (1996), Tensile ductility, slow

crack growth, and fracture mode of ternary B2 iron aluminides at room temperature,

Intennetallics, Vol. 5, p 185-193.

10. Stoloff, N. S. Iron aluminides: present status and future prospects. Materials

Science & Engineering. A258, 1998, l-l~

29

30

ACCOUNT STATEMENT

,,

APPENDIXES

i,

,i

LIST OF PUBLICATION

Zuraidah Mohd Yasin, Zuhailawati Hussain And Sunara PurwadariaStudies on corrosion behavior of Fe-AI intermetallic in natrium chloride solution.Proceeding of National Metal Conference (2006) Kolej Universiti Kejuruteraan UtaraMalaysia.

Zuhailawati Hussain, Zuraidah Mohamad Yassin, Ahmad Badri Ismail and LuayBakir Hussain,Mechanical properties studies on Cr alloyed FeAl.Proceeding of P SU-UNS International Conference on Engineering and Environment­ICEE-2007, May 10-11,2007, Prince ofSongkla University

H. Zuhailawati, M. N. Ahmad FauziMechanical Properties of Iron Alumininides Intermetallic Alloy with MolybdenumAddition

Proceeding of International Conference on Advancement of Materials andNanotechnology 29th May - Ist June (2007), SIRIM

Zuhailawati Hussain, Zuraidah Mohamad Yassin, Ahmad Badri Ismail and LuayBakir Hussain,Mechanical properties studies on Cr alloyed FeAl.Songklanakarin Journal of Science and Tec~nology (has been submitted)

\,

31

9th • 10th December 2006

"

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U.MU ·KEU(HtA..~· t(£a~KNOWLEDGE' SINCERITY' EXCELLENCE

"Sustainable Metallurgy Towards k-economy"

Pulra Palace Hotel,Kangra Penis.

Organized By:School Of Materials Engineering.i<Jllej Universiti Kejuruteraan UtaraMllaysia

NATIONAL METALLURGICAL CONFERENCE 2006(NMC2006)

. IDlEd UIIVSlSm IlEJUIUTEIAAI UTAIIA MAlAYSIA

IJft1

- -'---.-~~~~ ~--'-_.__:--..:.;.- '-~.~.~.:_-:-~~"'l:".,--------~-.-~~-~~_.. ,~f:;~ :-::..:-~ ~~_.=:-._.

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:-:_:-:.: ::-::'~-:';~=:.{'':'~~':f:':o/::':--'J:.~"",:-:, '~-.. '~ ': ~ -~ :. "~:.~""

'"..:.;,;(:~.:.-: ,". ~ ~-"~~"~~;'~':; ..~.,. - : : ~·,·.:·:,:'.i:;.: ::, .

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NMC2006

STUDIES ON CORROSION BEHAVIOR OF FE-ALINTERMETALLIC IN NATRIUM CHLORIDE SOLUTION

Zuraidah Mohd Yasin, Zuhailawati Hussain and Sunara Purwadaria

Accepted 28/1112006

School ofMaterials and Mineral Resources Engineering, Engineering Campus, Universiti SainsMalaysia, 14300, Nibong tebal, Penang, Malaysia

Introduction

Iron aluminides based on Fe3AI and FeAIpossess unique properties and have attractedconsiderable attention as potential candidatesfor warm structural application and aspromising substitutes for stainless steels andcast irons at room temperature due to theirexcellent oxidation and corrosion resistance[I). The aluminides also offer low materialcost, and low density (as compared with Fe­and Ni-based alloys). In recent years, therehas been considerable interest in thesynthesis and processing of intermetalliccompounds by means of mechanicalalloying. Mechanical alloying is a highenergy ball milling process that involves·.repeated welding and fracturing of powderparticles. This technique can produce finepowders with a nfuioscalegrain size and ahomogeneous distribution, of dispersoid,which is expected to improve the. ambienttemperature ductility and high temperaturestrength of intermetallic compounds.Although these materials are mainlydeveloped for high temperature applications,ambient temperature aqueouS forrosion canalso be a serious problem for 'its durability.This can happen when the alloys~ possiblyexposed to humid environment containingsulphates and/or chlorides, either duringalloy processing stage or during idling timeof the finished components [2]. Where thecorrosion resistance of the metal has to beenhanced, passivity~inducing elementsshould be added.

A systematic investigation has beenconducted by the present authors to fabricatetribological FeAI-Cr intermetallic alloys by amechanical alloying approach. Cr was chosenas the ternary alloying element because it has

been reported that addition of Cr responsiblefor offering passivity, and add up to localizedcorrosion resistance. The present work isundertaken to investigate the electrochemicalcorrosion behavior of the iron aluminides in anatrium chloride solution to understand theeffect of Cr addition on the electrochemicalcorrosion behaviour of iron aluminides.

Experimental

MaterialsThe nominal compositions of alloys used inthe present study are Fe-25AI, Fe-24.375AI­2.5Cr, Fe-23.75AI-5Cr, Fe-23.125AI-7.5Cr

~ and Fe-22.5AI-10Cr (in wt%) with theaddition of 0.5% n-heptane and 0.5% zincstearate. Bulk samples were prepared bymechanical alloying in a planetary mill for 4

.. -hours, pressing at 360 MPa and sintered at1000°C for 2 hours before cut into lOmm xlOmm x 5um} dimension. The sample wasmounted with one end soldered to a copperwire.

Apparatus and ProceduresPassivation behaviour of iron aluminides wasstudied using P9~ntiodynamic polarizationtechnique with a scan rate of O.167mV/s in3.56wt% NaCI solution at room temperature.The set-up consisted of a potentiostat drivenby Gamry Instrument software and anelectrochemical corrosion cell. The cell usedfor the polarization studies was a beaker with500ml capacity, graphite bar as counter

i electrode, copper sulphate electrode as a, reference electrode and iron aluminides

sample as a working electrode. Aftercorrosion test, the sample was observedunder a scanning electron microscope.

77

NMC2006 Accepted 2811112006

.Results and discussion

4 -12 -10 -8

Fe~21.5Al-10Cr

'::It/

Fe-23.125AI-7.SCr

Fe-23.75Al-SCr

Logi(Ncm')

-6

Fe-25A1

resistance of ~he alloy. Fig. 2 shows that allsamples are preferentially attacked by pittingcorrosion after they are polarized higher thantheir pitting potentials. In addition, it maynaturally occur on passive metal or alloysdue to passive film breakdown at potential ~Epitt or due to mechanical action which candamage the pas,sive film at potential < Epitt.Pitting corrosion is initiated at locations atwhich the passive film is weaker than otherareas due to less Cr content. Results alsoconfirm that aluminides without Cr additionare more susceptible to pitting corrosioncompared to other aluminides with the Craddition.

Figure 1: Potentiodynamic polarizationcurves ofFe-AI-Cr in 3.56wt% NaCI media

Figure 2: SEM image of alumTnides afterpolarization showing pitting attack (a) Fe­25Al (b) Fe-24.375Al-2.5Cr (c) Fe-23.75AI­5Cr (d) Fe-23.l25AI-7.5Cr (e) Fe-22.5AI­IOCr

Potentiodynamic polarization curves of allthe four Fe-AI-Cr alloys and Fe-AI binary arepresented in Figure 1. These Fe-AI-Cr alloysexhibit a broad passive-pitting behavior. Theaddition of Cr tends to slightly increase thepassive pitting breakdown potential of thealloys and thus slightly increase pitting

I,

78

ConclusionPotentiodynamic polarization of ionaluminides in NaCI media shows the Fe-AI­Cr are susceptible to pitting corrosion.Thepitting corrosion resistance and thepassivation potential range of Fe-AI-Cralloys increases with increasing of Crcontent.

References1. Gedevanishvili, S. and Deevi, S.C.

Processing of iron aluminides bypresu'reiess sintering·' through Fe+AIelemental route." Material Science andEngineering A325 (2002) 163-176

2. Charlot, F., Gaffet, E., Zeghmati, B.,Bernard, F. and Niepce, J.C.Mechanically activated synthesis studiedby x-ray diffraction in the Fe-AI system.Materials Science and Engineering A262(1999) 279-288

3. Balasubramaniam,R. Alloy DevelopmentTo Minimize Room Temperaturehydrogen Embrittlement In IronAluminides. Journal of Alloys andCompounds. 253(1997) 148-151

PC-O-16: The Effect of Veneer Layers on the Bending Shear Strength andDelamination of Laminated Veneer Lumber (LVL) from Oil Palm Trunk (OPT)Mohd AriffJamaludin, Kamarulzaman Bin Nordin, ShahrilAnuar Bin Bahari, Mansur

Ahmad

PC-O-17: Effects of Cryogenic Treatment and Refrigerated Air on Tool WearWhen Machining Medium Density FiberboardJudith Gisip, Rado Gazo, Harold A. Stewart

MA-O-I: Fatigue Behavior Stirred SiCpReinforced LM6 Aluminum Composites:

Effect of Blade Angles and Stirring SpeedsAl Emran Ismail

MA-O-2: Formation of Nitrogen-Pearlite in The Diffusion Bondiqg of Sialon to316L Stainless SteelP. Hussain, o. Mamat, M. Mohammad, W.M.N. Wan Jaafar

MA-O-3: Forensic Analysis of Ring Main Unit (RMU) FailureIszuan Shah Syed Ismail, Ng Guat Peng

MA-O-4: Comparison between Palm Oil Derivative and Commercial Thermo­Plastic Binder System on the Prope.-aes of The Stainless Steel 3161. SinteredPartsR. Ibrahim, M. Azmirruddin, G. C. W~i, L. K. Fong, N. I. Abdullah, K. Omar, M.Muhamad, S. Muhamad .

MA-O-5: Mechanical Properties of Iron Alumininides Intermetallic Alloy withMolybdenum Addition .. . ~ , .... >

H. Zuhailawati, M. N. Ahmad Fauzi

113

114

115

116

117

118

119

MA-O-6: Magnetic Properties of Hot Pressed NdFeB Magnet 120M. H. Saleh, F . Ismail, E. A. Othman

MA-O-7: The Product\On and Characterization of Near Stoichiometric NdFeB- 121Type HDDR Powder .A. Shaaban, M.Hashim, q~..Harris

MA-O-8: Fracture Toughness Measurements on Ni-W Alloy Microbeams 122Fabricated by Lithography and ElectrodepositionA.S.M.A. Haseeb, K. Bade

MA-O-9: Corrosion Behaviour of Al Alloys in Seawater 123Siti Radiah Mohd Kamarudin, Muhamad Daud, Mohd Shariff Sattar, Abd. RazakDaud "

MA-O-IO: NbAl Intelligent Material through Mechanical Alloying and Spark 124Plasma SinteringKaruna Chinniah, Kawasaki Akira

MA-O-ll: Wear Behavior of Tin-Fly Ash Composites 125H. Yazid, M. Harun, Z. Selamat, M. S. Sattar, M. Jalil

xiii

Oral Abstracts

ialinless

fech 2/3,

MA-O-5

Mechanical Properties of Iron Alumininides Intermetallic Alloywith Molybdenum Addition

H. Zuhailawati*, M. N. Ahmad Fauzi

School ofMaterials and Mineral Resources Engineering, Engineering Campus, Universiti SainsMalaysia, 14300, Nibong Tebal, Penang, Malaysia

*zuhaila@eng.usm.my

AbstractIron aluminides are attractive for elevated temperature applications due to their low density, lowmaterial cost and good high temperature mechanical properties. In addition, they exhibit excellentcorrosion resistance in oxidizing and sulphidizing atmospheres. However, the main drawbackconcerning their possible technological applications is its ductility in the cast form at roomtemperatures.

ssful'I • A. II was

oiland

eand

I:··~..

In this work, FeAI-based alloys..with and without molybdenum addition were fabricated bysintering of mechanically alloyed p,?wders in order to investigate the effect of molybdenum oniron aluminide mechanical properties. The nominal compositions of alloys used in the presentstudy were Fe2SAI, Fe24.38AI2.5Mo, Fe23.7SAIS.OMo and Fe23. 13AI7.5Mo (inwt%) with theaddition of 0.5% n-heptane and 0:5% zinc stearate. Bu1k samples were prepared by mechanicalalloying in a planetary mill for 4 hours, pressing at 360 MFa and sintering at 1000 DC for 2,b.ours.For compression tests, specimens were cut into 2mm x: 2mm x 5 mm size and tested at roomtemperature using Instron machine. The phase identification and microstructure of theconsolidated material was examined by x-ray diffraction and scanning electron microscopecorrespondingly.

Table I shows the ~important results of the compressive stress-strain curves of FeAI sinteredmaterials. It can be seen that Mo addition up to 2.5wt% significantly increased the ultimate stfe';',S

and ultimate strain in tfOmpressive mode. The improvement in these properties is due to solidsolution hardening [I] as confirmed by XRD analysis. However, the addition of Mo more than2.5wt% was accompanied by a reduction in both properties. The decrease in these properties isprobably caused by the presence of Morich precipitate particles as observed in the microstructureof the FeAI which may act as stress concentrator [2].

Keywords: Iron-aluminide Intermetallic/Alloying Element! Mechanical Properties.

References[I] Y. Sun, F. Xue, J. Mei, X. Yu, Z. L. Zhang, Scripta Metallurgica et Materialia, VoI.32,

No.8, pp-118 l-ll 84, 1995.[2] P. Banerjee, P. Balasubramaniam, R. Sripta Materialia, Vo1.38, No 7, pp.1143-ll47, 1198.

ti tedrt' f IIT bl 1 Ca e ompreSSlOll prope les 0 a oy mves 19aAlloy Composition Ultimate Stress Ultimate Strain (mm/mm)

(wt%) ; (MPa), ,

Fe-25AI 142 0.046

Fe-24.8AI-2.5Mo 221 0.063

Fe-23.75A1-5Mo 151 0.042

Fe-23.13AI-7.5Mo 128 0.041Fe-22.5AI-I0Mo 123 0.028

119

Mechanical Properties Of Iron Alumininides Intermetallic Alloy WithMolybdenum Addition

H. Zuhailawati*, M. N. Ahmad Fauzi

School of Materials and Mineral Resources Engineering,Engineering Campus, Universiti Sains Malaysia,

14300, Nibong Tebal, Penang,Malaysia

zuhaila@eng.usm.my

Abstract:In this work, FeAI-based alloys with and without molybdenum addition were fabricated by sinteringof mechanically alloyed powders in order to investigate the effect of molybdenum on ironaluminide mechanical properties. Bulk samples were prepared by mechanical alloying for 4 hours,pressing at 360 MPa and sintering at 1000 °C for 2 hours. The specimens were tested incompression at room temperature using Instron machine. Th.e phase identification andmicrostructure of the consolidated material wa1l. examined by x-ray diffraction and scanningelectron microscope correspondingly. Results ~ow that 2.5wt%Mo addition significantly increasedthe ultimate stress and ultimate strain in compressive mode due to solid solution hardening.However, the addition of Mo more than 2.5wt% was accompanied by a reduction in both propertiescaused by the presence of Mo-rich precipitate particles.

1. IntroductionIntermetallic compounds have been

the subject of scientific interest for morethan 50 years because their I attractivephysical and mechanical properties. Inrecent years research mostly focusecr'on theuse of monolithic intermetallic materialsbased on aluminides as replacements fordenser structural materials such as steels orsuperalloys for high temperature service.Among the intermetallics, iron aluminidesare attractive for elevated temperatureapplications due to their low density, lowmaterial cost and good high temperaturemechanical properties (1). In addition theyexhibit excellent corrosion resistance inoxidizing and sulphidizing atmospheres. Ofthe iron aluminides, FeAI, has a B2 structure

and exists over a wide range of Alconcentrations at room temperatures (36­50at%). Iron aluminides based on FeAIexhibit better oxidation resistance than Fe3AIalloys, have lower densities compared to thesteels and commercial iron based alloys andexhibit higher electrical resistivitycomparable to the commercial metallicheating elements. These properties allowthem to be considered as high temperaturestructural materials, gas filters, heating

\, elements, furnace fixtures, heat-exchangerpiping, catalytic converter substrates,automotive exhaust systems and chemicalproduction system (1,2).

Iron aluminides were previouslyexcluded from the realm of structuralmaterials because of their brittleness at

1

Figure 1(b) to (e) shows the patternsfrom the FeAI with different amount of Moaddition. For Mo containing Fe-AI mixtures,

'[

f~~J

). d)

r~ e).\

200

3. Results & DiscussionFigure 1 shows the diffraction pattern

correspond to the five different alloys. Thephase was identified by comparing the peakpositions and intensities with those listed inthe Intenational Committee of DiffractionData (rCDD) files. Figures 1 (a) of the X-raydiffraction pattern shown by FeAI mixturesample is corresponding to the FeAI (FileNumber: 33-0020). From FeAI binarydiagram the expected major phase to exist atcomposition of 25% Al with sinteringtemperature of 1000°C is FeAI phase. Fromthe ICnD file the lattice structure of FeAIintermetallic compound is BCC structure.

before observed under scanning electronmicroscope. The phase composition of thleconsolidated material was examined by x­ray diffraction analysis.

Figure 1: The XRD pattern of the alloyformed with different composition of Mo

" (a) O%Mo (b) 2.5%Mo (c) 5.0%Mo (d)7.5%Mo (e) 10.0%Mo

2-1I1ETA: 2D GRAPHICS300-------------...

[collnt$) F!,~ )~25B J

2. MethodologyIn this work, FeAI-based alloys with

and without molybdenum addition werefabricated by sintering of mechanicallyalloyed powders in order to investigate theeffect of molybdenum on iron aluminidemechanical properties. The ~ nominalcompositions of alloys used in the J:resentstudy were Fe-25AI, Fe-24.38AI-2.5lV1o, Fe­23.75AI-5.0Mo, Fe-23.l3AI-7.5Mo and Fe­22.50AI-10Mo (in wt%) with the addition of0.5% n-heptane and 0.5% zinc stearate.

Bulk samples were prepared bymechanical alloying in a planetary mill for 4hours, pressing at 360 MPa and sintering at1000 °c for 2 hours. For compression tests,specimens were cut into 2mm x 2mm x 5mm size and tested at room temperatureusing Instron machine. The specimens wasmechanically polished to Illm gradediamond powder and etched with 5% Nital

ambient temperatures and poor strength atelevated temperatures. Recent research anddevelopment activities have demonstratedthat adequate engineering ductility (6) canbe achieved in the aluminides through thecontrol of microstructure and alloyadditions. Both tensile and creep strengths ofthe aluminides are substantially improved byalloying with refractory elements, whichresults in solution hardening and particlestrengthening. The high-temperaturestrength and fabricahility of FeAI isimproved by alloying this material withmolybdenum, carbon, chromium, andvanadium (l,6).

Thus, in the present study, FeAIintermetallic powder will be synthesizedusing mechanical alloying and consolidatedvia powder metallurgy route, particularlycold pressing and sintering. The main goalof this study is to investigate the effect ofalloying element of molybdenum, on themicrostructural and properties of FeAl.

2

single phase of FeAI (File Number: 33­0020) is also detecteed. XRD studiesindicate that the Mo present in solid solutionin the alloyed intermetallics of Fe-AI-Mo.The ternary diagram of Fe-AI-Mo show theaddition of Mo in range of 2.5-10% withsintering temperature of 1000oe, theexpected phase to exist is FeAl.

Fig.2 shows the obtainedmicrostructures for sintered Fe-AI-Mo alloyswith different Mo contens, Whiteprecipitates can be observed mainly on the'grain boundaries for sample containing Mo.The amount of this precipitates obviouslyincreases with increasing Mo content. Thecompositions of the preciptates determinedby EDX is shown in Fig. 3, which indicatesthe presence of a large concentration of Mo.

As reported by [7], Mo are found tobe effective in strenthening aluminidesthrough solid solution effect. On the otherhand, room temperature ductility decreaseswith addition of this element. However, inthe present work it was found that theaddition of 2.5% Mo has given the result thattensile strength and tensile strain are thehighest value (Fig. 4 and Fig. 5).

The decrease in compressive strengthin the present work probably is due to thepresence of Mo-rich precipitates in Fe-AI­Mo intermetallic. As discusses preyiously by[8], these precipitates can be assume as the'flaw' which act as stress conce~rators,

thereby becoming the sources of prematurefailure. When stress is applied, crack tendsto first initiate around the precipitates, thengrows, and propagate leading to fracture.

It can be said that after the onset ofthe plastic deformation, due to the presenceof more stress concentrators, the appliedstress for Fe-AI-5.0%Mo, Fe-AI-7.5%Moand Fe-AI-lO.O%Mo is lower than Fe-AI­2.5%Mo.

i,

a)

b)

c)

d)

e)

Figure 2: SEM image for sample Fe-AI withdifferent composition of Mo (a) O%Mo (b)2.5%Mo (c) 5.0%Mo (d) 7.5%Mo (e)lO.O%Mo 2000X

3

~\cdIlC32~.·I(IefW1'Wl)"8I)C 13.oa~2tM 11:11;2'LS<>«: 21

1.to 2.'. J.9G 4.&0 5.80 '-01 T.OO 1Leo t.08 10.00 11.00 12.00 13.'

4. SummaryBulk samples of FeAl-based intermetallicalloys with w molybdenum addition wereprepared by mechanical alloying, pressingand sintering. Results show that 2.5wt%Moaddition significantly increased the ultimatestress and ultimate strain in compressivemode due to solid solution hardening.However, the addition of Mo more than2.5wt% was accompanied by a reduction inboth properties caused by the presence ofMo-rich precipitate particles.

53.75 17.9405:22 06.19

12.5707.21

10.90· 21.8217:57 ···46.85

FeKMoL

OK

AI

o

.1

.4

Kerst

U No

Figure 3: EDX for Fe-AI-Mo sample atregion X

Fig. 4: Compressive strength ofthe Fe-Al­Mo intermetallic

5. ACKNOWLEDGEMENTThe financial supported received from

Universiti Sains Malaysia under Short TermGrant -6035145 is acknowledged.

References" [1] N. S. Stoloff, Materials Science &

Engineering. A258, pp. 1-14,1998[2] A. Saigal, W. Yang, Journal ofMaterialsProcessing Technology. 132, pp. 149-156,2003[3] K. Wolski,. G. Le Caer, P. Delcroix, R.Fillit, F. Thevenot, J. Le Coze, MaterialsScience and Engineering, A207, pp. 97-104,1996[4] D.A. Ealman, J.R. Dahn, G.R. MacKay,R.A. Dunlap, Journal of Alloys andCompounds. 266,pp.234-240, 1998[5] F. CharIott, E. Gaffet, F. Bernard, J.C.Niepce, Materials Science and Engineering.A262,pp.279-288,1999[6] N.S. Stolof, C.T. Liu, S.C. Deevi,Intermetallics. 8, pp. 1313-1320,2000[7] Y. Sun, F. Xue, J. Mei, X. Yu, Z. L.

I

, Zhang, Scripta Metallurgica et Materialia,Vo1.32, No.8, pp-1181-1184, 1995[8] P. Banerjee, P. Balasubramaniam, R.Sripta Materialia, Vo1.38, No 7, pp.1143­1147, 1198

10

107.55

M)(x:npcsitim(\~;g

25 5 7.5

IIIbca,JUliticn(WO~

25

o

o

0.070.00

0.05.~ 0.04~ 0.03

0.020.01

o

Fig. 5: Strain of the Fe-AI-Mo intermetallic

4

007&PEC-S

l PSU-UNS International Conference on Engineering andEnvironment -ICEE-2007, Phuket May10-11, 2007

Prince of Songkla University, Faculty of EngineeringHat Yai, Son khla, Thailand 90112

MECHANICAL PROPERTIES STUDIESON Cr ALLOYED FeAl

Zuhailawati Hussain*, Zuraidah Mohamad Yassin, Ahmad Badri Ismail and Luay

Bakir Hussain

School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia,14300, Nibong Tebal, Penang, Malay,sia.

zuhaila@eng.usm.my

Abstract: Phase identification and mechanicalproperties ofFeAI intermetallic alloys with addition ofCr were obtained. The alloys were produced withpowder metallurgy technique through mechanicalalloying method. Compression test was carried outand some insights on the alloys mechanical propertieswere withdrawn. The main effect ofCr element on theFeAI structure was related with the improvement ofthe compressibility ductility andfracture strength. The· •results showed that in compressive mode, the fracturestrength and ductility of FeAI sintered alloys wereincreased with an increase in Cr composition due to'solid solution strengthening and formation ofpassivelayer..Key Words: Iron-alum/nide IntermetalliclAlloyingElement! Mechanical Properties

1. INTRODUCTION

Intermetallic compounds have beed the subject ofscientific interest for more than 50 years because theirattractive physical and mechanical pr<1Jllerties. Inrecent years research mostly focused on the use ofmonolithic intermetallic materials based onaluminides as replacements for denser structuralmaterias such as steels or superalloys for hightemperature service. The main goal of thesedevelopments are weight reduction, propertiesoptimization or the tailoring of properties for specificapplications for instance high-temperature super­conducting aluminum alloys with Nb additions, low­density alloys with Mg additions and good corrosionresistance with Fe additions.

Among the intermetallics, iron aluminides base onFeAl and Fe3Al are attractive for elevated temperatureapplications due to their low density, low material costand good high temperature mechanical properties [1].In addition they exhibit excellent corrosion resistancein oxidizing and sulphidizing atmospheres. Of the iron

aluminides, FeAl, has a B2 structure and exists over awide range of Al concentrations at room temperatures(36-50at%). Iron aluminides based on FeAl exhibitbetter oxidation resistance than Fe3AI alloys, havelower densities compared to the steels and commercialiron based alloys and exhibit higher electricalresistivity comparable to the commercial metallicheating elements. These properties allow t hem to beconsidered as high temperature structural materials,gas filters, heating elements, furnace fixtures, heat­exchanger piping, catalytic converter substrates,automotive exhaust systems and chemical productionsystem [2].

However, in the FeAI compound, likewise in theother intermetallic aluminides, the main drawbackconcerning their possible technological applic.ations isits ductility in the cast form at room temperatures andprocessing problems due to hydrogen embritlement(HE). Several methods have been proposed tominimize HE like oxide coatings (to minimizehydrogen pick-up from the environment), heattreatments (to produce a partially recrystallizedmicrostructure) and alloying with passivity-inducingelements [3].

Considerable studies have been done to improveiron aluminide mechanical properties throughoutcontrol of microstructure and alloy composition. Ninepassivity-inducing elements were alloyed to Fe3AI toproduce intermetallic composition Fe-24AI-5M where

" M=Ti, Zr, V, Nb, Ta, Cr. Mo,W and Si [4]. Only theCr- and Ti-alloyed intermelallic exhibited ductility.The other intermetallics were brittle due to theprecipitation of additional brittle phase

The objective of the present work was toinvestigate effect of Cr alloying element on themechanical properties and structure of Fe-AIintermetallic.

2. EXPERIMENTAL PROCEDURE

'"

250

1~ .200

.=~ 150=b'" 100~EE 50~

Fe-25A1 Fe-24.38AI-2.5Cr Fe-23.75AI-5Cr5 Fe-23.13-7.5Cr

\ Alloy'c-- . _

o

[------------------·--·----------1

Figure 1 illustrates the diffraction patternscorrespond to the five different prepared alloys. Figurel(a) of the X-ray diffraction patterns shown by FeAImixture sample is corresponding to the FeAI (FileNumber: 33-20) and FeAl2 (File Number: 33-19)phases but the intensity of FeAIz peak is very lowrelative to FeAI. Figure l(b) to (e) illustrates thepattern from the Fe-AI mixtures with different amountof Cr composition. For Cr containing FeAt mixtures,only single phase of Fe2AICr (File Number: 42-1486)is detected. Another feature in the XRD pattern is thatthe peaks of(220) approximately at 28=44° are shiftedto lower angles with increasing Cr addition whichindicate that Cr present in solid solution in the alloyedintermetallics of Fe-AI-Cr The atomic radius, r, of Fe,AI and Cr are 0.1241 nm, 0.1431 nm and 0.1249 nmrespectively. Therefore the decrease in latticeparameter of Fe2AlCr is due to the replacement oflarger AI atom by smaller Cr atom.

Compression tests were carried out from each ofthe obtained alloys. Each test was repeated for threedifferent specimens from the same alloy. Thecompression results from each of the alloys wereobtained from the average of the three tests. Theimportant results of the compressive stress-straincurves of FeAI alloys were shown in Figure 2 andFigure 3. Figure 2 shows the dependence of thefracture stress (fracture strength) of FeAI alloys on thepresence of Cr alloying elements. The increased

~ fracture strentgh of FeAl with 2.5-10% of Cr is mostlikely attributed to solid solution strentghening of Cras confirmed by XRD analysis. Solid solutionstrentghening occurs when the dislocation mobility ina soUd is restricted by the introduction of solute atoms[5]. The presences of Cr solute atoms in FeAr alloysintroduce discrete barriers which restrict the motion ofthe dislocation glide that would lead to strengthening.

reAl l""" ,I '.:0 a~

t:X

III

ttl'

«t

«1

~

~.-'Ott ~.§

" ",ti<

1'8

3. RESULTS AND DISCUSSION

One of the common approaches used recently, toenhance the ductlity of the FeAl intermatallic alloyhas been the alloying with elements. In thisinvestigation, the effect of the addition of Cr as wellas the effect of Cr content to the FeAI intermetallic •was explored.

Commercial metal powders of Fe, AI and Cr wereemployed to produce FeAI-based alloys in the presentstudy. The nominal compositions of alloys used in thepresent study were Fe-25AI, Fe-24.38AI-2.5Cr, Fe­23.75AI-5.0Cr and Fe-23.I3AI-7.5Cr (in wt %) withthe addition of 0.5% n-heptane and 0.5% zinc stearate.Mechanical alloying of the mixture powder wascarried out in a high energy planetary-type ball millingsystem at a rotational speed of 300rev/min for 4 hours.Consolidation of the mechanically alloyed powderswas performed through cold pressing under a pressureof 360 MPa followed by sintering at 1000 °C for ahold time of 2 hours.

Mechanical properties of the sintered compactswere evaluated by compression test. For compressiontests, rectangular specimens with dimensions of 2 x 2x 5 mm

3sizes were sectioned from the compacts by

diamond cutting. All surfaces of the specimens werepolished with SiC paper. These specimens were testedat room temperature using Instron Machine. Thestructure of the sintered compacts was characterizedby X-ray diffraction (XRD). .

i 9 I f ~ ! I I ~ 3

~

Fig. 2: Fracture strength of the Fe-AI-Cr intermetallic

Fig. 1: The XRD pattern of the alloy (a) Fe-25AI (b)Fe-24.375AI-2.5Cr (c) Fe-23.75AI-5Cr (d) Fe­23.125AI-7.5Cr

Alloying with Cr also produced a higher straincompared to the base intermetallic which indicate theimprovement in ductility. The ductility results of thepresent study are in agreement to earlier report whereit was shown that Cr additions provide a passive layer

2

ICEE20070109MECHANICAL PROPERTIES STUDIES ON Cr ALLOYED FeAI

Zuhailawati Hussain*, Zuraidah Mohamad Yassin, Ahmad Badri Ismail and Luay Bakir HussainSchool of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia,

14300, Nibong Tebal, Penang, Malaysia.zuhaila@eng.usm.my

Abstract:Phase :dentijication and mechanical properties of FeAl intermetallic alloys with addition of Cr

were obtained. The alloys were produced with powder metallurgy technique through mechanical alloyingmethod. Compression test was carried out and some insights on the alloys mechanical properties werewithdrawn. The main effect of Cr element on the FeAl structure was related wirth the improvement of thecompressibility ductility andfracture strength. The results showed that in compressive mode, the fracturestrength and ductility of FeAl sintered alloys were increased with an increase in Cr composition due to'solid solution strengthening andformation ofpassive layer..

Key Words:Tron-aluminide IntermetallidAlloying Element!Mechanical Properties

ICEE20070110Effects of Superheated Steam and Hot

Air on the Mechanica~Properties of Rubberwood

Ram Yamsaengsung *, Surapit TabtiJlngPrince of Songkla University, Faculty of Engineering, Thailand

*Authors to correspondence should be addressed via email: ram.y@psu.ac.th

Abstract:A pilot-scale rubberwood dryer was constructed and injected with superheated steam and hot air

to study the effect ofthe hybrid system on the drying rate and mechanical properties ofthe wood. A total of300 pieces ofrubberwood boards each with dimensions of1 m long x 3 in. wide x I in. thick were stackedin 1 m x 1 m 1.7 m (60 ft3) pal/ft. The stack was impinged with alternating cycles ofsuperheated steam andhot air. The time required for conventional drying was 129 hours and the time schedule for the hybriddrying system was only 64 hours r~ulting in a 66.7% reduction. After being dried, the rubberwood boardswere mechanically testedfor static bending, compression strength, hardness and shear strengths. From themechanical tests, hybrid drying system using superheated steam and hot air had no significant effect on themean shear strength parallel to grain; however; the mean compression strength parallel to grain wasreduced by 24.23% and the mean MaR by 21.35%. Nonetheless, the mean MOE was increased by30.41% and the mean of hardness by 16.4%.

KeyWords:Rubberwood drying,Drying, Supeheated Steam, Stack Temperature

. ,

)mu-UNS International Conference on Engineering and En.vi:l?OJJ1Ytertt£-2001 '---'------'"~- ..........:_._.__;--....;.......;;.....;..--...;..-4--'----"-~;;..........-,-....,.._..:..,...-'--C.;.~-+-~p ~~

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.'on the surface of the intermetallic [3]. [3] hasexplained the effect of Cr addition on embritlement ofFeAl by mixed potential analysis. He conclude~ thatthe rate of hydrogen liberation on the passIvatedsurface of the Cr-alloyed iron aluminide is muchlower than that surface of the binary aluminide.Addition of higher content of Cr is beneficial toincrease ductilities by inducing thicker passive filmwhich delay hydrogen entry into FeAl alloys.Therefore, ductility is impmved because hydrogenembritlement of,iron aluminides has been minimized.

0.09 .,

0.08 j0.07

0.06

.5 005E .ii5 0.04

0.03

0.02

0.01 .

o +--Fe-25AI Fe-24.38AI- Fe-23.75AI- Fe-23.13-

2.5Cr 5Cr5 7.5Cr

Alloy

Fig. 3: Strain of the Fe-Al-Cr intermetallic

4. CONCLUSION •The room temperature ductility of iron aluminide .

can be enhanced by the addition of passivity-inducingelement of Cr to the base iron aluminide. Cr exists insolid solution in the iron aluminide which provideadditional fracture strength to the base metal.

5. ACKNOWLEDGEMENTThe financial supported received from Universiti

Sains Malaysia under the grant (Short Term Grant ­6035145 is acknowledged. Also the author would liketo thank TPLN-USM for the financial supported.

I

5. REFERENCES

[1] N.S. Stoloff, "Iron aluminides: preserlt status andfuture prospects", Materials Science &Engineering, 1998,A258, pp.I-14

[2] Saigal, A. and Yang, W. Analysis of milling ofiron aluminides. Journal of Materials ProcessingTechnology. 132,2003,149-156

[3]R.Balasubramaniam, "Hydrogen in IronAluminides", Journal of Alloys and Compound,2002,330-332, pp. 506-510.

[4]P. Banerjee and R. Balasubramaniam, "MechanicalBehavior of Cromiujm and Titanium Alloyed IronAluminides with Mischmetal Addition", ScriptaMaterialia, 1998, Vol. 38, No.7, pp. 1143-1147.

[5] U. Husni, Development of y-TiAI-based alloyproduced by hot -pressing and arc melting routes.2005, MSc Thesis, Universiti Sains Malaysia.pp75-79

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