Spray forming of high density sheets

SDMA 2013 - 5th Int. Conf. on Spray Deposition and Melt Atomization – 23-25 Sept. 2013 - Bremen, Germany

1

Spray forming of high density sheets C. Meyer

1, N. Ellendt

1, L. Mädler

2, H. R. Müller

3, F. Reimer

4, V. Uhlenwinkel

1

1

Foundation Institute of Materials Science (IWT), Department of Production Engineering, 2

University of Bremen, Germany 3

Wieland-Werke AG, Ulm 4

Zollern BHW Gleitlager GmbH & Co. KG, Braunschweig

Corresponding author: Volker Uhlenwinkel, [email protected]

Abstract

Porosity is one of the most important quality criteria of spray-formed materials in the as-

sprayed condition. Typically, spray-formed sheets have a porous rim close to the substrate

and depending on the spray conditions cold or hot porosity may also be present in the core of

the deposit. This porosity has to be removed or minimized to make further processing steps

such as rolling, forging or extrusion possible.

In this paper, the influence of both substrate temperature and deposit surface temperature on

porosity in spray-formed sheets is studied.

For this purpose spray forming experiments (sheet size 1000 mm x 250 mm) were carried out

using three different materials: aluminium-bronze, tin-bronze and a nitriding steel. For the

copper-base alloys preheated steel-substrates with different temperatures were moved through

a scanning spray cone. In the case of steel a ceramic substrate at room temperature was used.

In addition to the variation of the substrate temperature, the gas to metal mass flow ratio

(GMR) was varied to achieve different deposit surface temperatures. During the run the sur-

face temperature in the deposition zone was measured using a scanning, multi-wavelength

pyrometer. Samples of the deposits were polished and rasterized by light microscopy. The

local porosity was characterized by digital image analysis.

The influence of the substrate temperature and the GMR on the porosity in the vicinity of the

substrate is evaluated and discussed in detail. The impact of the deposit surface temperature

on the porosity was analyzed and is discussed as well. It was found that the deposit surface

temperature has a strong impact on porosity for spray-formed sheets.

Finally, experimental results were used to develop a new approach to predict the porosity in

spray-formed sheets. The results clearly show the dependence on material properties. This

approach can be used to identify process parameters to generate high density sheets in the

future.

Keywords: spray forming, density, porosity, sheets, modeling


2

1 Introduction

The density or porosity is one of the most important quality criteria of spray-formed materials

in the as-sprayed condition, because porosity reduces mechanical, thermal and electrical prop-

erties [Pay1993, Liu1999, Sri2004, Sas2004].

In literature two main types of porosity are described [Ell2010, Mue2004, Cui2009]. One type

is called cold porosity, which corresponds to cold spray conditions. This porosity is related to

deposition of particles with a low liquid fraction leaving an insufficient liquid fraction in the

deposition zone for filling interstices or cavities between deposited solid particles. The other

type of porosity is known as hot porosity or gaseous porosity. This type of porosity is caused

by a high liquid fraction at the deposit surface as a consequence of hot spray conditions. Im-

pinging particles entrap gas into the deposit, which is not dissolved and cannot leave the de-

posit due to solidification. A minimum porosity within these extreme bounds of high porosity

conditions is technological very favored.

Typically spray-formed sheets have a highly porous rim in the vicinity of the substrate,

caused by cold deposition conditions. Usually this porosity has to be removed to make further

processing steps such as rolling, forging or extrusion possible. The formation of porosity is

not limited to the vicinity of the substrate, because hot or cold porosity may also occur in the

core of the deposit depending on the spray conditions. This porosity has to be minimized to

allow further processing steps as well. Once the porosity is below a certain level the remain-

ing porosity can be fully eliminated by metal forming processes like forging, rolling or hot

isostatic pressing [Ger2002, Gra1995, Wal2006].

Previous studies correlated porosity with process parameters such as gas to metal mass flow

ratio (GMR) or liquid fraction in the spray [Ell2010, Wat1990, Ach2010, War1997]. However

these correlations are only valid for the same spray forming setup in terms of atomizer design,

spraying distance, substrate movement and substrate geometry.

Cai et al. proposed a theoretical model to predict porosity in spray-formed deposits [Cai1997].

This model is based on the idea that the calculated solid fraction of particles in the spray

forms a sphere packed structure and the remaining liquid fraction fills the resulting cavity in

the structure. The porosity is then calculated by the difference of the cavity volume of the

sphere packed lattice to the volume of the liquid fraction [Cai1998]. This approach may be

suitable to predict porosity for very cold spray conditions, where the deformation of imping-

ing particles can be neglected, because they are already solid. But this model is not suitable

for typical spray forming conditions, where a significant deformation of the particles takes

place.

Uhlenwinkel et al. revealed the dependency of the porosity of Ni-based superalloys on the

surface temperature during deposition of ring deposits [Uhl2006, Uhl2007]. This correlation

is believed to be independent of the atomizer design, deposit geometry or other geometric and

kinetic conditions. It has not been proven if the effect of surface temperature on porosity is

transferable to other deposit geometries or other materials.

In the past it has been shown that the preheating of the substrate reduces porosity in vicinity

of the substrate during spray forming of steel tubes [Wah1993, Aif2003]. Systematic investi-

gations on porosity in the vicinity of the substrate of spray-formed sheets are not available in

literature.


3

2 Experimental setup and analysis

In order to analyze the influence of the thermal conditions of substrate and deposit on the po-

rosity, spray forming experiments were carried out using three different materials: aluminium-

bronze, tin-bronze and nitriding steel. The chemical composition of the investigated materials

is given in table 1.

Tab. 1 Chemical composition of tested materials in weight %

Element (wt %) Cu Sn Ti Al Ni Fe

Sn-bronze base 15.5 0.25

Al-bronze base

10 5 4

Element (wt %) Fe C Mn Cr Mo Si

Nitriding steel base 0.07 - 0.11 0.9 - 1.2 3.7 - 4.1 0.4 - 0.6 0.1 - 0.4

A scheme of the experimental setup is shown in Fig. 1. The feed stock material is inductively

melted in a vessel under nitrogen or argon in case of the steel.

Before the spray run started the spray chamber was purged with nitrogen to achieve an oxy-

gen content less than 100 ppm. A low carbon steel substrate (AISI 1010, 250 x 1000 x 24

mm³) was inductively heated for the copper alloys. In the case of steel a ceramic substrate (20

x 250 x 250 mm) was used without preheating.

The melt was poured into the preheated tundish. A ceramic nozzle was placed at the bottom

of the tundish, where the melt flowed into the atomization area of a free fall atomizer. Once

the spray is in steady state condition the substrate is moved through the spray cone, which is

scanning crosswise to the substrate velocity. In the deposition zone a spray-formed sheet was

built.

An overview of the process parameters is given in table 2. The preheating temperature of sub-

strate and the GMR was varied in the different experiments. The thicknesses of the bronze

and the steel deposits were in the range of 5 – 10 mm and 10 – 15 mm, respectively.

Fig. 1 Experimental setup: spray forming of sheets including deposit surface temperature

measurement using a scanning pyrometer

Atomizer Pyrometer

Spray coneInduction heater

Deposit

Deposition areaThermocouplePreheated substrate

Measurement of

surface temperature


4

Tab. 2 Process parameters of spray forming experiments

Parameter unit Al-bronze Sn-bronze Nitridingsteel

Vessel purge gas -- N2 N2 Ar

Atomizer gas -- N2 N2 N2

Melt temperature °C 1205 - 1212 1110 1675 - 1677

Melt superheat K ~ 132 ~ 143 ~ 150

Nozzle diameter mm 6.25 - 6.5 5 5

Melt flow rate kg/s 0.31 - 0.39 0.34 0.28 - 0.3

Gas melt flow kg/s 0.11 - 0.32 0.17 0.16 - 0.34

GMR -- 0.28 - 0.86 0.5 0.53 - 1.13

Spraying distance mm 600

Scan angle ° 10.5

Substrate velocity mm/s 15 - 30 20 10 - 13

Substrate material -- AISI 1010 AISI 1010 Al2O3 base

Substrate preheating °C 760 - 1127 800 - 890 RT

During the run the temperature at the surface of deposit or substrate is measured with a scan-

ning mirror (Sensortherm Galayxy SC 11) and a multi wave length pyrometer (Sensortherm

Metis MQ 11). The measurement line is schematically illustrated with a blue line in Fig. 1. In

addition to the pyrometer measurement thermocouples are placed in the center of the thick-

ness of the substrate.

3 Measurement techniques and methods

After deposition the deposit was cooled and cut as shown in Fig. 2. The samples were pol-

ished and recorded on a raster using light microcopy. The porosity was then determined using

image analysis of the combined overall image of each sample.

Fig. 2 Scheme of sampling and characterization area for porosity analysis

analyzed area

10 mm 125 mm

de

po

sit

thic

kn

ess

~20 mm


5

the specific heat capacities of the deposited materials were measured either using differential

scanning calorimetry (Netzsch DSC 404C) or were calculated with Thermocalc using the

calphad method [And2002]. The specific heat can be derived from the specific heat capacity.

4 Results and discussion

4.1 Thermophysical properties

The specific heat capacity of the Al-bronze is shown in Fig. 3 (black dotted curve). It shows a

solidus temperature Tsol of 1037 °C and liquidus temperature Tliq of 1080 °C. Evaluating the

area of the peak between Tsol and Tliq gives a latent heat of fusion hfus of 240 kJ/kg.

Fig. 3 Thermophysical property cp of the Al-bronze, Sn-bronze and the nitriding steel

In contrast to the Al-bronze the Sn-bronze (gray curve) has a wider melting range with Tsol =

785 °C and Tliq = 967 °C. The latent heat of fusion hfus is about 124 kJ/kg, which is only 50%

of hfus of the Al-bronze.

The black curve in Fig. 3 represents the nitriding steel. These data were calculated using

Thermocalc (Database TCFE3). The melting range of the nitriding steel is narrow, with Tsol =

1479 °C and Tliq = 1527 °C. The resulting latent heat hfus is 265 kJ/kg. This is in the same

order of magnitude as the Al-bronze, but it releases a large amount of hfus in a temperature

interval of only 20 K as indicated with the sharp peak of cp. It can be seen that these materials

differ in the melting range as well in the amount of heat of fusion.

4.2 Temperature measurement in the substrate and at the deposit surface

Fig. 4 shows the measured temperatures of sections of an Al-bronze deposit produced with

three different GMRs and three different substrate preheating temperatures.

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

300 500 700 900 1100 1300 1500 1700 1900

Sp

eci

fic

he

at

cap

aci

ty [

J k

g-1

K-1

]

Temperature [°C]

Al-bronze

Sn-bronze

Nitriding steel


6

Fig. 4 Measured temperatures at the deposit surface and inside of the substrate for differ-

ent GMR and substrate preheating during deposition of Al-bronze

The time 0 s marks the entry of the corresponding thermocouples when they are in the meas-

uring zone of the scanning pyrometer. The deposition time (4 - 14 s) is also marked in the

diagram. Depending on the substrate preheating and the spray conditions different tempera-

ture profiles were created.

The blue and black dotted lines represent the temperature measurement of the thermocouples

TC1 and TC3 inside the substrate for low preheating temperatures. During the movement of

the substrate from the heating position (see Fig. 1) to the deposition zone the substrate looses

heat to the surroundings by convection and radiation. Here the substrate temperatures slightly

decrease until the thermocouples reach the deposition zone. In this case the corresponding

pyrometer measurement and thermocouples show a difference of about 50 K. During deposi-

tion the deposit surface temperature increases to a maximum at about 66% of deposition time

(see Fig. 4), after which the deposit surface temperature decreases.

The red dotted line shows the temperature of the thermocouple TC2 for a preheating tempera-

ture of 1225 °C. In this case the substrate looses more heat before entering the deposition

zone and has a temperature of about 1125 °C, when the first particles impinge on the substrate

at the position of TC2.

Here the thermocouple TC2 and the corresponding pyrometer measurement do not show sig-

nificant differences. Although the deposited material of the spray is colder than the substrate,

only little influence of the deposition on the temperature of the inner substrate (TC2) can be

recognized.

In spite of this the deposit surface temperature in the deposition zone strongly decreases for

about 6 s. After this point the deposit surface temperature stays almost constant during depo-

sition time.

Immediately upon completion of deposition the surface temperature slightly increases because

the substrate is still hotter than the deposit and heats the deposit.

The influence of the different GMR on the deposit surface temperature is clearly visible. A

low GMR means hot spray condition. This leads to the highest maximum temperature

750

800

850

900

950

1000

1050

1100

1150

1200

1250

-50 -40 -30 -20 -10 0 10 20 30 40 50

Tem

pera

ture

[°C

]

Time [s]

Pyrometer, GMR 0.46

Thermocouple 1, GMR 0.46

Pyrometer, GMR 0.68


Pyrometer, GMR 0.86


deposition time

substrate preheating


7

(1025 °C) in the deposition zone, even though the substrate was only slightly preheated

(800 °C). This is in contrast to this the highest GMR, where the lowest maximum temperature

in the deposition zone was 960 °C. Consequently the maximum temperature in the deposition

zone for a mid-range GMR of 0.68 reaches 1000 °C. In this case substrate preheating shows

no recognizable effect on the maximum temperature in the deposition zone.

4.3 Porosity in the vicinity of the substrate

The porosity in the vicinity of the substrate is important for coating processes or multilayer

processes where a bonding between the substrate and the deposit is required. Reducing the

porous rim of spray-formed sheets can also help to increase the material yield in this process.

For the analysis of near substrate porosity the vicinity of the substrate is defined as a height of

250 µm from the substrate + five percent of the total deposit thickness.

Fig. 5 shows the effect of the substrate preheating on porosity in the vicinity of the substrate

evaluated by image analysis for Al-bronze. For preheating temperatures in the range of 800

°C a porosity in the vicinity of the substrate of 4 – 5.5 % is found. While the substrate tem-

perature is increased, the porosity in the vicinity of the substrate is reduced. The lowest poros-

ity was achieved with a substrate preheating of 1100 °C. At this temperature almost dense

material with a porosity of less than 0.5 % was made. Further increase of the substrate pre-

heating temperature leads to a slight increase of porosity. This might be explained by the

spray or impact conditions. Preheating of the substrate to temperatures above Tsol of the de-

posit creates a certain amount of liquid fraction at the deposition zone near to the substrate.

The particles first impinging on the substrate have their origin near the edge of the spray cone.

Typically here are the smallest and coldest particles. The combination of a certain amount

liquid fraction at the deposit surface and cold impinging particles causes slightly elevated po-

rosity due to forming mechanisms of hot porosity.

Fig. 5 Influence of substrate preheating on porosity in the vicinity of the substrate (Al-

bronze)

750 800 850 900 950 1000 1050 1100 11500

1

2

3

4

5

6

Substrate temperature [°C]

Poro

sity

[%

]

GMR 0.28

GMR 0.38 - 0.46

GMR 0.51 - 0.69

GMR 0.84 - 0.86


8

The influence of the GMR on the porosity at the vicinity of the substrate was not significant.

This means that the porosity in the vicinity of the substrate is strongly governed by the tem-

perature of the substrate immediately before deposition.

The same analysis of substrate preheating temperature and its influence on porosity in the

vicinity of the substrate was carried out for Sn-bronze as well.

It is obvious that the high temperatures of the substrate leading to dense materials in the vicin-

ity of the substrate of an Al-bronze, cannot be transferred to other materials directly, because

of lower melting temperatures. For example the Tliq of the Sn-bronze is 967 °C, and therefore

a substrate temperature of 1100 °C would melt and destroy the deposit.

In order to compare the results for both alloys the dimensionless substrate equivalent enthalpy ℎ��∗ (equation 1 and 2) is introduced. A scheme of the dimensionless equivalent substrate

enthalpy is shown in Fig. 6.

ℎ��,�� = � 0 �� < ��,�� − ��,�� ∙ ��,�� ,� < � < ��,�0 �� ,� < � � (1)

ℎ��∗ =ℎ�� − ℎ��,�� − ℎ��,�� ℎ ��,� (2)

In the melting range the sensible heat ℎ��,� is calculated from the specific heat capacity �

at Tsol,dep of the deposit and the temperature difference �� − ��,�� of the preheated sub-

strate and Tsol,dep using Eq. 1. The dimensionless equivalent enthalpy of the substrate ℎ��∗ is

calculated from Eq. 2. With ℎ�� being the enthalpy of the deposit material related to

the substrate temperature, the enthalpy of the deposit material ℎ��,�� at Tsol , the sen-

sible heat ℎ��,� and the heat of fusion ℎ ��,� of the deposit material.

A dimensionless equivalent enthalpy of the substrate of zero means that the substrate has Tsol

of the deposit when the first particles impinge. According to this, a dimensionless equivalent

enthalpy of the substrate of “1” means that the substrate has the liquidus temperature Tliq of

the deposit, when the first particles impinge.

Fig. 6 Dimensionless equivalent substrate enthalpy as a function of temperature

Tliq,depTsol,deph

hsens,dep

hfus,dep

0

1

h*sub

T


9

Fig. 7 Effect of dimensionless substrate enthalpy on porosity in the vicinity of the substrate

Using Equation 2 the porosity in the vicinity of the substrate is plotted versus the dimension-

less equivalent enthalpy of substrate in Fig. 7. Here temperature intervals of 25 K are used to

obtain the average porosity for different substrate temperatures and dimensionless equivalent

substrate enthalpies, respectively.

Comparing Fig. 5 und Fig. 7 both diagrams show the same trend. Rather high porosity in the

vicinity of the substrate for low dimensionless equivalent enthalpies of the substrate and low

porosity materials for dimensionless equivalent enthalpies of the substrate of 0.25 – 0.5. A

little increase of the porosity in the vicinity of the substrate can be recognized for dimension-

less equivalent enthalpies of substrates greater than 1.

For both alloys the Al-bronze and the Sn-bronze the minimum porosity could be achieved

when the substrate had a dimensionless equivalent enthalpy close to 0.5. This might be ex-

plained with thermal conditions of the particles first impinging on the substrate.

Particles that have their origin at the edge of the spray cone, typically are the smallest and

coldest particles, consequently particles impinging directly at the deposit surface are fine and

already solidified. But a certain amount of liquid fraction is necessary to avoid interstitial po-

rosity and achieve a low porosity. Therefore preheating of the substrate above Tsol is neces-

sary to create the right amount of liquid fraction at the interface of deposit and substrate for

almost pore free material.

4.4 Porosity in the deposit

The transient deposit geometry is calculated with the transient temperature profile according

to Achelis et al. [Ach2010]. This allows relating local porosities to deposit surface tempera-

tures.

-1 -0.5 0 0.5 1 1.50

1

2

3

4

5

6

Dimensionless enthalpy of substrate [-]

Poro

sity [

%]

Al-bronze

Sn-bronze


10

Fig. 8 Influence of deposit surface temperature on porosity of Al-bronze

While spray forming of superalloy rings Uhlenwinkel et al. have correlated the porosity and

the deposit surface temperature [Uhl2006]. The porosity of the Al-bronze depends on the de-

posit surface temperature in the same manner. Fig. 8 shows the influence of the deposit sur-

face temperature on the porosity. Here temperature intervals of 25 K are used in analogous

manner to the study of the substrate preheating in order to determine the mean porosity and

their standard deviation.

The same analysis of the deposit surface temperature and its influence on the porosity has also

been performed for the Sn-bronze and the nitriding steel. Because the deposit surface temper-

ature is not suitable to compare results or to transfer results to other materials, the dimension-

less enthalpy of the deposit surface ℎ��! ∗ is introduced in Eq. 3 and 4 in analogous manner to

the dimensionless enthalpy of the substrate (Eq. 1 and 2).

The sensible heat ℎ�� in the melting range related to the temperature Tsurf of the deposit sur-

face is calculated with Eq. 3. Equation 4 is used to calculate the dimensionless surface enthal-

py ℎ��! ∗ of the deposit, with ℎ��! � − ℎ�� being the difference between surface

enthalpy and solidus enthalpy and ℎ ��,� the heat of fusion of the deposit material.

ℎ��! � = � 0 �� < ��,�� − ��,�� ∙ ��,�� ,� < � < ��,�0 �� ,� < � � (3)

ℎ��! ∗ =ℎ��! � − ℎ�� − ℎ��! �ℎ ��,� (4)

800 850 900 950 1000 1050 11000

1

2

3

4

5

6

Deposit surface temperature [°C]

Po

rosity [

%]


11

Fig. 9 Influence of dimensionless deposit surface enthalpy on porosity

Fig. 9 illustrates the influence of the dimensionless deposit surface enthalpy on porosity. All

materials show the same trend. A low dimensionless surface enthalpy leads to high porosity.

With increasing dimensionless enthalpy of the deposit surface the porosity decreases.

This effect takes place until a minimum porosity for dimensionless surface enthalpies around

zero is reached, which can be explained with cold porosity formation.

Even though all materials show the same trend, the magnitude of porosity for the three inves-

tigated materials is very different. The nitriding steel is highly porous with a minimum porosi-

ty of about 5 %, while the aluminum-bronze has a minimum porosity in the range of 1 %.

The Sn-bronze only shows porosities smaller than 0.5 % for dimensionless surface enthalpies

of 0.25 - 0.5.

One reason for these different levels might be the thermophysical properties (see section 4.1)

of the materials. The steel has a narrow melting range combined with highest heat of fusion.

This results in the highest porosity level. The opposite thermophysical properties has the tin-

bronze, it has the widest melting range and the smallest heat of fusion of all studied materials

and therefore only little porosity. The Al-bronze is to be ranked between the other materials in

terms of melting range, heat of fusion and porosity. Since the influence of thermophysical

properties on the mechanisms of forming porosity is unclear, further studies are necessary in

this field.

Another parameter that requires attention is the chemical composition of the Sn-bronze. In-

vestigations of Müller et al. have shown that the porosity can be reduced for about 1 %, when

titanium is added to tin-bronzes [Mue2004]. In this paper the investigated tin-bronze has an

amount of about 0.25 % by weight titanium. Thus the titanium content of the alloy may have

reduced the porosity due to the chemical reaction of nitrogen and titanium. Entrapped nitro-

gen in the pores reacts to titanium-nitrides and reduces porosity.

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 10

5

10

15

20

25

Dimensionless enthalpy of deposit surface [-]

Poro

sity [%

]

Al-bronze

Sn-bronze

Nitriding steel


12

5 Conclusion

The experimental investigations on the porosity in vicinity of the substrate have shown that

this porosity is governed by the preheating of the substrate. The spray conditions or the GMR

do not have a significant effect on porosity at the vicinity of the substrate. Furthermore the

approach of the dimensionless equivalent enthalpy of the substrate can be used to transfer

results to other materials and find the right preheating temperature for low porosity materials

in the vicinity of the substrate. Low porosities in the vicinity of the substrate were found for

both the Al-bronze and the Sn-bronze for dimensionless equivalent enthalpy of the substrate

of 0.25 - 0.5.

The relation of porosity and deposit surface temperature has been proven for spray-formed

sheets and different materials as well. The approach of the dimensionless enthalpy of the de-

posit surface is suitable to describe porosity in the deposit. Nevertheless the level of porosity

depends on the type of material, so this approach is not able to predict absolute porosity, but it

is able to predict conditions when the formation of low porosity materials is expected. All

investigated materials had a minimum porosity when the deposit surface had a dimensionless

enthalpy of 0 - 0.25.

Since a dimensionless enthalpy of the deposit surface of 0 - 0.25 leads to low porosity materi-

als, it is necessary to achieve this enthalpy over the entire deposit thickness. Here further

work is necessary in order to control the deposit surface temperature over the entire deposi-

tion zone.

6 Literature

[Pay1993] R.D. Payne, A.L. Moran, R.C. Cammarata: Relating porosity and mechanical

properties in spray formed tubulars, Scripta Metallurgica et Materialia, 29

(1993) 907-912.

[Liu1999] P.S. Liu, T.F. Li, C. Fu: Relationship between electrical resistivity and porosity

for porous metals, Materials Science and Engineering: A, 268 (1999) 208-215.

[Sri2004] V.C. Srivastava, A. Schneider, V. Uhlenwinkel, K. Bauckhage: Effect of

porosity and reinforcement content on the electrical conductivity of spray

formed 2014-Al alloy + SiCp composites, Journal of Materials Science, 39

(2004) 6821-6825.

[Sas2004] K.Y. Sastry, L. Froyen, J. Vleugels, E.H. Bentefour, C. Glorieux: Effect of

Porosity on Thermal Conductivity of Al-Si-Fe-X Alloy Powder Compacts,

International Journal of Thermophysics, 25 (2004) 1611-1622.

[Ell2010] N. Ellendt, O. Stelling, V. Uhlenwinkel, A. von Hehl, P. Krug: Influence of

spray forming process parameters on the microstructure and porosity of Mg2Si

rich aluminum alloys, Materialwissenschaft und Werkstofftechnik, 41 (2010)

532-540.

[Mue2004] H.R. Müller, K. Ohla, R. Zauter, M. Ebner: Effect of reactive elements on

porosity in spray-formed copper-alloy Billets, Materials Science and

Engineering A, 383 (2004) 78-86.

[Cui2009] C. Cui, A. Schulz, K. Schimanski, H.W. Zoch: Spray forming of hypereutectic

Al-Si alloys, Journal of Materials Processing Technology, 209 (2009) 5220-

5228.

[Ger2002] R. Gerling, F.P. Schimansky, G. Wegmann, J.X. Zhang: Spray forming of Ti

48.9Al (at.%) and subsequent hot isostatic pressing and forging, Materials

Science and Engineering: A, 326 (2002) 73 - 78.

[Gra1995] P.S. Grant: Spray forming, Progress in Materials Science, 39 (1995) 497-545.


13

[Wal2006] M. Walter, M. Stockinger, J. Tockner, N. Ellendt, V. Uhlenwinkel: Spray

forming and post processing of superalloy rings, Superalloys 718, 625, 706

and Derivatives, (2006) 429-440.

[Wat1990] G. Watson: Thermal and Microstructural Characterization of Spray Cast

Copper Alloy Strip, First International Conference on Spray Forming;

Swansea; UK; 17.-19. Sept. 1990, (1990).

[Ach2010] L. Achelis, V. Uhlenwinkel, R. Ristau, P. Krug: Transient temperatures and

microstructure of spray formed aluminium alloy Al-Si sheets,

Materialwissenschaft und Werkstofftechnik, 41 (2010) 498-503.

[War1997] L. Warner, C. Cai, S. Annavarapu, R. Doherty: Modelling Microstructural

Development in Spray Forming: Experimental Verification, Powder

Metallurgy, 40 (1997) 121-125.

[Cai1997] W.D. Cai, E.J. Lavernia: Modeling of porosity during spray forming, Materials

Science and Engineering: A, 226-228 (1997) 8-12.

[Cai1998] W. Cai, E.J. Lavernia: Modeling of porosity during spray forming: Part I.

Effects of processing parameters, Metallurgical and Materials Transactions B,

29 (1998) 1085-1096.

[Uhl2006] V. Uhlenwinkel, N. Ellendt, M. Walter, J. Tockner: Spray Forming and Post

Processing of Superalloy Rings, in: Continuous Casting, Wiley-VCH Verlag,

2006, pp. 247-255.

[Uhl2007] V. Uhlenwinkel, N. Ellendt: Porosity in spray-formed materials, in: D.Y.

Yoon, S.J.L. Kang, K.Y. Eun, Y.S. Kim (Eds.) Progress in Powder Metallurgy,

Pts 1 and 2, Trans Tech Publications Ltd, Stafa-Zurich, 2007, pp. 429-432.

[Wah1993] J.M. Wahlroos, T.P. Liimatainen: Interface adherence of spray formed

compound tube, Second International Conference on Spray Forming; Swansea;

UK; 13.-15. Sept. 1993, (1993) 225-234.

[Aif2003] Kontrollierte Wärmezufuhr zur Beeinflussung von Homogenität und Haftung

sprühkompaktierter Rohre aus Stahl, Abschlussbericht AiF Projekt 12727N,

(2003).

[And2002] J.-O. Andersson, T. Helander, L. Höglund, P. Shi, B. Sundman: Thermo-Calc

and DICTRA, computational tools for materials science, Calphad, 26 (2002)

273 - 312.

Documents

Spray forming of high density sheets