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NiAl

Mechanical Properties of Porous NiAl with

Unidirectional Pores

2012 2

NiAl

Mechanical Properties of Porous NiAl with

Unidirectional Pores

2012 2

Mechanical Properties of Porous NiAl with

Unidirectional Pores

by

Ji-Woon Lee

A THESIS

Submitted to the faculty of

INHA UNIVERSITY

in partial fulfillment of the requirements

for the degree of

MASTER OF ENGINEERING

Department of Metallurgical Engineering

February 2012

i

List of Figures

List of Tables

Abstract

1. 1

2. 4

2.1 4

2.1.1 4

2.1.2 11

2.1.3 14

2.2 Nickel Aluminide 17

2.2.1 -NiAl 19

2.2.2 22

3. NiAl 25

3.1 25

3.2 26

3.3 29

3.3.1 29

3.3.2 29

3.4 35

ii

3.4.1 35

3.4.2 38

3.5 40

4. NiAl 42

4.1 42

4.2 43

4.3 44

4.3.1 44

4.3.2 47

4.4 54

4.4.1 54

4.4.2 59

4.5 65

5. 67

68

iii

List of Figures

Figure 2-1. Schematic diagram for an exterior view of lotus-type porous

metal 5

Figure 2-2. Temperature dependence of hydrogen solubility in solid and

liquid of various metals under the hydrogen pressure of 0.1MPa

6

Figure 2-3. Schematic diagram of pore nucleation and growth in

unidirectional solidification in gas atmosphere 8

Figure 2-4. Averaged pore diameter and porosity of lotus-type porous

stainless steel under various pressure of mixed gases composed

of (a) hydrogen and argon or (b) hydrogen and helium 10

Figure 2-5. Schematic diagram of mold casting technique 12

Figure 2-6. Schematic diagram for the melting part of continuous zone

melting technique 13

Figure 2-7. Schematic diagram of continuous casting apparatus 15

Figure 2-8. Ultimate tensile strength and yield strength of lotus-type porous

copper in the direction parallel and perpendicular to pore axis as

a function of porosity 16

Figure 2-9. Schematic diagram of compressive stress-strain curve of

lotus-type porous metal 18

Figure 2-10. Ni-Al phase diagram 20

Figure 2-11. B2 crystal structure (space group Pmm, CsCl prototype) of

iv

NiAl 21

Figure 2-12. Critical resolved shear stress for (a) a slip in 'soft'

crystals, (b) a{112} and a{110}slip in 'hard' crystals

23

Figure 3-1. Photograph of a universal testing machine 28

Figure 3-2. Optical micrographs of pore morphology of lotus-type

porous NiAl cross-sections (a) perpendicular and (b) parallel to

the solidification direction 30

Figure 3-3. X-ray diffraction patterns of lotus-type porous NiAl (a) before

and (b) after homogenization heat treatment 31

Figure 3-4. Compressive stress-strain curves of (a), (b) nonporous NiAl and

(c), (d) lotus-type porous NiAl with the solidification direction

(a), (c) parallel and (b), (d) perpendicular to the compressive

direction 32

Figure 3-5. Scanning electron micrographs of (a) lotus-type porous and (b)

nonporous NiAl 36

Figure 3-6. Scanning electron micrographs of crack tip blunting of

lotus-type porous NiAl with the solidification direction (a)

perpendicular and (b) parallel to the compressive direction 37

Figure 3-7. Scanning electron micrographs of multi-crack for lotus-type

porous NiAl. A magnified view of A and B in (a) is shown in

(b) and (c), respectively. 39

Figure 4-1. Photographs of (a) a universal testing machine and (b) a heating

chamber near Jigs 45

Figure 4-2. Optical micrographs of microstructure in (a), (b) lotus-type

v

porous and (c), (d) nonporous NiAl rods. (a), (c) and (b), (d)

show transverse and longitudinal cross sections, respectively.

46

Figure 4-3. Compressive stress-strain curves of (a), (c), (e) nonporous NiAl

and (b), (d), (f) lotus-type porous NiAl testing at (a), (b) 298

K, (c), (d) 673 K and (e), (f) 873 K 48

Figure 4-4. Optical micrographs of exterior features of compressive

specimens for (a), (c) nonporous NiAl and (b), (d) lotus-type

porous NiAl after compression test at 673 K. Compressive

direction is (a), (b) parallel and (c), (d) perpendicular to the

solidification direction. 51

Figure 4-5. Optical micrographs of exterior features of compressive

specimens for (a), (c) nonporous NiAl and (b), (d) lotus-type

porous NiAl after compression test at 873 K. Compressive

direction is (a), (b) parallel and (c), (d) perpendicular to the

solidification direction. 52

Figure 4-6. Yield strength variation of nonporous and lotus-type porous

NiAl with the solidification direction (a) parallel and (b)

perpendicular to the compressive direction as a function of

temperature 53

Figure 4-7. Optical micrographs of exterior features of porous specimen

after compression test at (a), (c) 673 K and (b), (d) 873 K;

compressive direction is (a), (c) parallel and (b), (d)

perpendicular to the solidification direction. 55

Figure 4-8. Scanning electron micrographs of specimen surfaces for

lotus-type porous NiAl with the solidification direction (a)

perpendicular and (b) parallel to the compressive direction after

compression tests 57

vi

Figure 4-9. Schematic diagram of applied stress to (a) sharp and (b) blunt

crack tips 58

Figure 4-10. Scanning electron micrographs of parallel lotus-type porous

specimen after compression test at (a) 298 K and (b) 673 K 60

Figure 4-11. Scanning electron micrographs of (a) parallel and (b)

perpendicular lotus-type porous specimen 62

Figure 4-12. Inverse pole figure maps of nonporous specimens with the

compressive direction (a) parallel and (b) perpendicular to the

solidification direction 64

vii

List of Tables

Table 3-1. Chemical compositions of NiAl ingot, lotus-type porous and

nonporous NiAl 27

Table 3-2. Mechanical properties of lotus-type porous and nonporous NiAl

with the solidification direction parallel and perpendicular to the

compressive direction at room temperature 34

Table 4-1. Mechanical properties of lotus-type porous and nonporous NiAl

with the solidification direction parallel and perpendicular to the

compressive direction at 298 K, 673 K and 873 K 49

viii

NiAl

,

. NiAl

.

NiAl ,

.

NiAl NiAl

, .

NiAl NiAl

4 , 2.5 .

.

NiAl - , 673

K NiAl .

,

. ,

.

ix

Abstract

Mechanical properties of intermetallic compound NiAl has been studied

by investigating the influence of unidirectional pores, when the pores are

introduced to the brittle material. Lotus-type porous NiAl was fabricated

by unidirectional solidification. A compression test was conducted at

ambient temperature and elevated temperatures. Crack behavior and

dislocation movement were analyzed and compared with nonporous NiAl

for more reliable elucidation after compression tests.

The deformation strain of the lotus-type porous NiAl was larger than

that of nonporous NiAl at ambient temperature. The porous NiAl exhibited

anisotropy in the specimens with pore axis in relation with compressive

direction. The deformation strain of the porous NiAl increased

approximately four times compared with nonporous NiAl. The energy

absorption ability increased approximately two and half times. Increased

energy absorption ability was postulated by crack tip blunting and

multi-cracking. At elevated temperature, the ductile to brittle transition

temperature decreased, and the deformation strain increased dramatically in

the porous NiAl at 673 K. Unidirectional pores affected the movement of

cracks and dislocations in the material, and these contributed to the

increased toughness of the material. Compressive strength of porous NiAl

with the solidification direction parallel to the compressive direction was

higher than that perpendicular. The anisotropy was caused by the stress

concentration differences along the direction of the pore axis and the

inherent anisotropy that originates from the crystal structure of NiAl.

1

1.

,

.

,

, .

, ,

,

.

15-95%

.

(,

, ) /,

, .

, ,

[1,2].

, ,

.

,

. ,

,

2

[3].

,

, , .

, ,

.

,

.

[4].

, 1979 Aoki[5] Ni3Al B

30%

.

,

TiAl Ni3Al . Ni-Al

L12 Ni3Al B2 NiAl

. NiAl Ni3Al , ,

,

.

[6,7].

NiAl -

3

.

NiAl

.

,

.

4

2.

2.1

,

. ( )

,

Imabayashi [8-10]

. Shapovalov[11]

,

(Gas-reinforced composite

metals) Gasar metals" . , Nakajima[12,13]

( )

. Nakajima

,

(Lotus-type

porous metals)" . Fig.

2-1 .

2.1.1

Fig. 2-2 0.1 MPa ,

.

. ,

.

/

5

Figure 2-1. Schematic diagram for an exterior view of lotus-type porous

metal

6

Figure 2-2. Temperature dependence of hydrogen solubility in solid and

liquid of various metals under the hydrogen pressure of 0.1 MPa[14]

7

. (liquid)

(solid)+(gas) "Gas-evolution crystallization

reaction"[15],

.

Fisher[16] ,

GPa

.

. 100-10

-1Pa

ppm

. /

.

/ .

/ ,

.

/ . ,

( )

, (Coarsening)

. Fig. 2-3

.

.

, /

.

,

.

, ,

. Hyun Nakajima[17]

8

Figure 2-3. Schematic diagram of pore nucleation and growth in

unidirectional solidification in gas atmosphere[18]

9

. /

,

. ,

,

.

.

Fig. 2-4

[19].

.

Sievert

[20]:

(1)

Cg, P, k , ,

. Boyle

. ,

. Fig. 2-4

, .

Sievert ,

.

, ,

. ,

.

10

Figure 2-4. Averaged pore diameter and porosity of lotus-type porous

stainless steel under various pressure of mixed gases composed of (a)

hydrogen and argon or (b) hydrogen and helium[19]

11

2.1.2

Fig. 2-5 (Mold

casting technique) . (Crucible)

.

Sievert ,

(Mold) . (Chiller)

, .

(Matrix)

, .

, ,

.

Cu, Mg

.

.

,

.

.

, Nakajima[21]

Fig. 2-6 (Continuous zone melting technique)

. (Holder) (Metal rod)

, Sievert

.

, (Blower)

.

12

Figure 2-5. Schematic diagram of mold casting technique[3]

13

Figure 2-6. Schematic diagram for the melting part of continuous zone

melting technique[21]

14

,

.

,

.

Nakajima[22] Fig. 2-7

(Continuous casting technique)

.

,

.

2.1.3

, [23,24]. Hyun[25]

Cu ,

-

.

. Fig.

2-8

,

.

,

. Hyun "Load-bearing

area model" . Balshin[26]

15

Figure 2-7. Schematic diagram of continuous casting apparatus[27]

16

Figure 2-8. Ultimate tensile strength and yield strength of lotus-type

porous copper in the direction parallel and perpendicular to pore axis as a

function of porosity[25]

17

(2)

K 1, K

3 .

. , Fig. 2-9 -

. (Plateau stress region)

- .

,

[1]. ,

[28.29]. ,

. Hyun[30]

Cu

, .

(Buckling) ,

(Collapse) (Densification) .

.

2.2 Nickel Aluminide

Ni-Al NiAl 1908 Gwyer[31]

,

18

Figure 2-9. Schematic diagram of compressive stress-strain curve of

lotus-type porous metal[30]

19

. , , ,

, ,

. , , ,

,

.

2.2.1 -NiAl

Fig. 2-10 Ni-Al . NiAl

, (Stoichiometric composition)

Ni 300K 1911 K .

, 2/3 5.86g/m3 3-8

.

NiAl B2 CsCl

. Fig. 2-11

Ni d-Al p

Ni-Al

.

[32].

NiAl

. NiAl 0.65 Tm

.

(Off-stoichiometric composition) Ni-rich Ni

Al , Al-rich Ni

[33].

20

Figure 2-10. Ni-Al phase diagram[34]

21

Figure 2-11. B2 crystal structure (space group Pmm, CsCl prototype) of

NiAl

22

2.2.2

NiAl ,

. NiAl

, ,

.

, (CRSS,

Critical resolved shear stress) [35-38].

Fig. 2-12 , CRSS

5-7 . "hard

orientation" {110}

. ,

"soft orientation" ,

{110} . ,

CRSS . "hard orientation"

, 800 K NiAl

(Anti-phase Boundary)

. 800 K

[39]. "soft orientation" , 77 K 400 K

, 400 K 1250 K

[6].

NiAl - (DBTT, Ductile to Brittle Transition

Temperature) {110}

, 5 Von

mises criterion .

23

Figure 2-12. Critical resolved shear stress for (a) a slip in 'soft'

crystals, (b) a{112} and a{110}slip in 'hard' crystals[35-38]

24

[40,41], 3 [42],

[43,44],

.

25

3. NiAl

3.1

(Ordered BCC structure)

NiAl (5.86 g/cm3), (1911 K),

(294.2 GPa), ,

. NiAl

,

[6,7]. ,

Ni

NiAl

.

[40,41], 3

[42],

[43,44],

.

(Lotus-type

porous metal)

[3]. ,

.

,

TiAl [3,45].

,

[45]. , NiAl Ni3Al[46]

. NiAl

,

26

.

3.2

(Ingot) Ni(99.99 wt%)

Al(99.99 wt%) .

(AQ325L, Sodick Corp., Japan)

10 mm, 170 mm (Rod) .

(Continuous zone melting technique)

2.5 MPa H2 NiAl

. NiAl NiAl 2.5 MPa

Ar .

(Optima 7300DV,

Perkinelmer Inc., USA) , Table 3-1

. NiAl 5 mm, 7.5 mm

, P

(3) .

(3)

, , 0

. (VHX200, Keyence Corp.,

Japan) .

, ,

. Fig. 3-1 (Model 4481, Instron

27

Table 3-1. Chemical compositions of NiAl ingot, lotus-type porous and nonporous NiAl

Specimen Ni (wt. %) Al (wt. %) etc. (wt. %)Ingot 68.83 31.01 0.16Porous 70.36 28.93 0.71Nonporous 70.74 29.09 0.17

28

Figure 3-1. Photograph of a universal testing machine

29

Corp., USA) 1.1 10-3/s

. 24 1474 K

-NiAl .

, .

, (JSM-5500,

Jeol Ltd., Japan) .

3.3

3.3.1

Fig. 3-2 NiAl

. ,

Fig. 3-2(b)

. NiAl 388 109

, 37.0 3.9%. Fig. 3-3 , X-

. NiAl, Ni3Al, Ni5Al3

, NiAl .

3.3.2

NiAl

Fig. 3-4 . ASTM E9-89a[47]

-

.

NiAl

. - NiAl NiAl

30

Figure 3-2. Optical micrographs of pore morphology of lotus-type porous

NiAl cross-sections (a) perpendicular and (b) parallel to the solidification

direction

31

Figure 3-3. X-ray diffraction patterns of lotus-type porous NiAl (a) before

and (b) after homogenization heat treatment

32

Figure 3-4. Compressive stress-strain curves of (a), (b) nonporous NiAl

and (c), (d) lotus-type porous NiAl with the solidification direction (a), (c)

parallel and (b), (d) perpendicular to the compressive direction

33

. , NiAl

.

,

. -

,

.

, -

. ,

4 .

Table 3-2

. .

NiAl NiAl

.

(Strain energy)

, (4) [48].

(4)

, f, ,

, -

. NiAl NiAl

,

.

NiAl

. ,

NiAl .

34

Table 3-2. Mechanical properties of lotus-type porous and nonporous NiAl with the solidification direction parallel and

perpendicular to the compressive direction at room temperature

Specimen Relation of pore axisto compressiondirection

Yield stress(MPa)

Fracture Strength(MPa)

Absorbed energy/volume(MJm-3)

Porous Parallel 312 452 19.0Perpendicular 85 128 5.2

Nonporous Parallel 417 467 9.8Perpendicular 298 339 7.3

35

3.4

3.4.1

NiAl Fig. 3-4

NiAl 4

, . Fig. 3-5

NiAl .

NiAl (Transgranular fracture)

. Fig. 3-4 3-5 ,

, .

(Crack)

. Fig. 3-6

.

, . ,

,

. ,

.

,

.

(Tip) ,

.

,

,

.

,

.

36

Figure 3-5. Scanning electron micrographs of (a) lotus-type porous and

(b) nonporous NiAl

37

Figure 3-6. Scanning electron micrographs of crack tip blunting of

lotus-type porous NiAl with the solidification direction (a) perpendicular

and (b) parallel to the compressive direction

38

.

(Surface energy) ,

(System)

.

.

,

. Fig. 3-7 .

,

.

, .

, ,

NiAl -

. (Matrix)

NiAl

.

3.4.2

NiAl

. Table 3-2

NiAl

.

.

[25].

.

(4)

39

Figure 3-7. Scanning electron micrographs of multi-crack for lotus-type

porous NiAl. A magnified view of A and B in (a) is shown in (b) and

(c), respectively.

40

(4) p, 0, p K ,

, , .

K 1 , K 3

[25]. K 0.8, 3.3

. ,

, .

, NiAl

,

.

NiAl .

NiAl

NiAl [36].

,

. Fig. 3-4 -

,

.

,

.

3.5

NiAl

.

.

41

1) NiAl , NiAl

, ,

.

2)

,

.

42

4. NiAl

4.1

(Ordered BCC structure)

NiAl (5.86 g/cm3), (1911 K),

(294.2 GPa), ,

. NiAl

,

[6,7]. ,

Ni

NiAl

.

[40,41], 3

[42],

[43,44],

.

-

[1]. (Plateau

stress region) ,

. ,

.

(Lotus-type porous metal)

[28,29]. ,

. ,

.

43

.

,

- [48]. ,

.

NiAl ,

.

,

. TiAl

. TiAl

,

[45]. ,

. ,

.

NiAl

,

.

4.2

(Ingot) Ni(99.99 wt%)

Al(99.99 wt%) .

(AQ325L, Sodick Corp., Japan)

10 mm, 170 mm (Rod) .

(Continuous zone melting technique)

2.5 MPa H2 NiAl

. NiAl NiAl 1.1 MPa

44

He .

(Optima 7300DV,

Perkinelmer Inc., USA) ,

Ni52Al48.

. 200

(VHX200, Keyence Corp., Japan)

.

Fig. 4-1(a) (Model 4481, Instron

Corp., USA) 1.1 10-3/s 673 K, 873 K

. (Chamber)

Fig. 4-1(b) (JIg)

, 10

. 5 mm, 7.5 mm

NiAl ,

24 1474 K .

, 90 mL

H2O, 10 mL H2O2, 10 mL HCl (Etching)

. , (JSM-5500, Jeol Ltd.,

Japan) .

(S-4300SE, Hitachi Ltd.,

Japan) .

4.3

4.3.1

Fig. 4-2

45

Figure 4-1. Photographs of (a) a universal testing machine and (b) a

heating chamber near Jigs

46

Figure 4-2. Optical micrographs of microstructure in (a), (b) lotus-type

porous and (c), (d) nonporous NiAl rods. (a), (c) and (b), (d) show

transverse and longitudinal cross sections, respectively.

47

NiAl .

, Fig. 4-2(b)

. , NiAl

NiAl (Columnar grain)

. [3].

311 69 , 32.7 4.7 % .

4.3.2

Fig. 4-3 NiAl NiAl

-

, Table 4-1 . NiAl

NiAl .

-

NiAl NiAl .

Fig. 4-3(a) 4-3(b) 3

. ,

.

4 ,

.

673 K

. - ,

,

.

-

[30,50].

.

873 K .

48

Figure 4-3. Compressive stress-strain curves of (a), (c), (e) nonporous

NiAl and (b), (d), (f) lotus-type porous NiAl testing at (a), (b) 298 K, (c),

(d) 673 K and (e), (f) 873 K

49

Table 4-1. Mechanical properties of lotus-type porous and nonporous NiAl with the solidification direction parallel and

perpendicular to the compressive direction at 298 K, 673 K and 873 K

Specimen Relation of pore axis to compression direction

Yield stress (MPa)

Strain to failure (%)

298 K 673 K 873 K 298 K 673 K 873 KPorous Parallel 321.5 204.3 78.7 4.53 - -

Perpendicular 87.6 65.9 32.3 3.19 - -Nonporous Parallel 401.1 344.9 230.3 1.03 2.07 -

Perpendicular 288.3 161.4 148.5 0.88 0.92 -

50

, NiAl NiAl .

673 K ,

NiAl ,

.

Fig. 4-4 673 K .

NiAl

, NiAl

. Fig. 4-5

873 K

(Slip band) .

-

.

NiAl NiAl

Fig. 4-2 Table

4-1 . NiAl NiAl

.

673 K

,

(Densification)

- . 873 K

673 K - .

NiAl NiAl

Fig. 4-6 . Fig. 4-6(a)

NiAl . , Fig. 4-6(b)

. NiAl 673 K

51

Figure 4-4. Optical micrographs of exterior features of compressive

specimens for (a), (c) nonporous NiAl and (b), (d) lotus-type porous NiAl

after compression test at 673 K. Compressive direction is (a), (b) parallel

and (c), (d) perpendicular to the solidification direction.

52

Figure 4-5. Optical micrographs of exterior features of compressive

specimens for (a), (c) nonporous NiAl and (b), (d) lotus-type porous NiAl

after compression test at 873 K. Compressive direction is (a), (b) parallel

and (c), (d) perpendicular to the solidification direction.

53

Figure 4-6. Yield strength variation of nonporous and lotus-type porous

NiAl with the solidification direction (a) parallel and (b) perpendicular to

the compressive direction as a function of temperature

54

, 673 K

.

. , 673 K

.

Fig. 4-7 NiAl

. -

, .

(Slip band)

45 , (Bending)

(Buckling) .

(Collapse) , .

4.4

4.4.1

NiAl - (DBTT, Ductile to Brittle

Transition Temperature) 673 K 873 K

,

[7]. DBTT

, , 30

[51,52].

30 , Ni-rich

NiAl DBTT 673 K 873 K .

, NiAl

. Fig. 4-3 - ,

NiAl DBTT 673 K, NiAl

55

Figure 4-7. Optical micrographs of exterior features of porous specimen

after compression test at (a), (c) 673 K and (b), (d) 873 K; compression

direction is (a), (c) parallel and (b), (d) perpendicular to the solidification

direction.

56

DBTT . , NiAl DBTT

, . , Fig.

4-4 4-5

. 673 K NiAl

, NiAl

NiAl .

673 K -

.

.

Fig. 4-8 . (Crack

tip) (Inclusion) (Void)

,

[53-55]. ,

. ,

,

. ,

. ,

. Fig. 4-9

.

,

. ,

. (Tip)

,

.

,

57

Figure 4-8. Scanning electron micrographs of specimen surfaces for

lotus-type porous NiAl with solidification direction (a) perpendicular and

(b) parallel to the compressive direction after compression tests

58

Figure 4-9. Schematic diagram of applied stress to (a) sharp and (b) blunt

crack tips

59

DBTT .

NiAl NiAl

.

(Slip line)

,

[28,56]. ,

, . Fig.

4-10 NiAl .

,

.

. NiAl DBTT ,

. Fig. 10(a)

,

. Fig. 10(b) 673 K

(Wavy)

. BCC

, BCC

{110}, {112} {123}

[57]. ,

.

4.4.2

-

.

60

Figure 4-10. Scanning electron micrographs of parallel lotus-type porous

specimen after compression test at (a) 298 K and (b) 673 K

61

NiAl NiAl

. NiAl

. (Stress concentration) (Defect)

,

.

(Bulk

material) .

NiAl

. NiAl

.

Fig. 4-3 673 K 873 K NiAl

- .

. Fig. 4-11

,

(Buckling) . ,

, (Collapse)

(Densification) .

, NiAl NiAl

. -

, NiAl .

NiAl NiAl

Fig. 4-6 .

. 673 K

, .

62

Figure 4-11. Scanning electron micrographs of (a) parallel and (b)

perpendicular lotus-type porous specimen

63

NiAl NiAl

,

.

NiAl

. NiAl BCC

[36]. ,

NiAl NiAl

.

. "hard orientation" ,

"soft orientation"

[6].

Fig. 4-12 NiAl

(EBSD, Electron Backscattered Diffraction)

. NiAl Fig. 12(a)

(IPF, Inverse Pole Figure) ,

"hard orientation" {100}

. Fig. 12(b) "soft

orientation" {110} . Fig. 4-3 -

.

NiAl Fig. 4-6

"hard orientation" ( ) 800K

NiAl

(APB, Anti-phase Boundary)

[39]. 800K

NiAl

64

Figure 4-12. Inverse pole figure maps of nonporous specimens with the

compressive direction (a) parallel and (b) perpendicular to the solidification

direction

65

. "soft orientation" (

) 400K

[6].

, NiAl NiAl

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5. Figure 2-1. Schematic diagram for an exterior view of lotus-type porous metal Figure 2-2. Temperature dependence of hydrogen solubility in solid and liquid of various metals under the hydrogen pressure of 0.1MPa Figure 2-3. Schematic diagram of pore nucleation and growth in unidirectional solidification in gas atmosphere Figure 2-4. Averaged pore diameter and porosity of lotus-type porous stainless steel under various pressure of mixed gases composed of (a) hydrogen and argon or (b) hydrogen and heliumFigure 2-5. Schematic diagram of mold casting technique Figure 2-6. Schematic diagram for the melting part of continuous zone melting technique Figure 2-7. Schematic diagram of continuous casting apparatus Figure 2-8. Ultimate tensile strength and yield strength of lotus-type porous copper in the direction parallel and perpendicular to pore axis as a function of porosity Figure 2-9. Schematic diagram of compressive stress-strain curve of lotus-type porous metalFigure 2-10. Ni-Al phase diagram Figure 2-11. B2 crystal structure (space group Pmm, CsCl prototype) of NiAl Figure 2-12. Critical resolved shear stress for (a) a slip in 'soft' crystals, (b) a{112} and a{110}slip in 'hard' crystals Figure 3-1. Photograph of a universal testing machine Figure 3-2. Optical micrographs of pore morphology of lotus-type porous NiAl cross-sections (a) perpendicular and (b) parallel to the solidification direction Figure 3-3. X-ray diffraction patterns of lotus-type porous NiAl (a) before and (b) after homogenization heat treatment Figure 3-4. Compressive stress-strain curves of (a), (b) nonporous NiAl and (c), (d) lotus-type porous NiAl with the solidification direction (a), (c) parallel and (b), (d) perpendicular to the compressive direction Figure 3-5. Scanning electron micrographs of (a) lotus-type porous and (b) nonporous NiAlFigure 3-6. Scanning electron micrographs of crack tip blunting of lotus-type porous NiAl with the solidification direction (a) perpendicular and (b) parallel to the compressive direction Figure 3-7. Scanning electron micrographs of multi-crack for lotus-type porous NiAl. A magnified view of A and B in (a) is shown in (b) and (c), respectively. Figure 4-1. Photographs of (a) a universal testing machine and (b) a heating chamber near JigsFigure 4-2. Optical micrographs of microstructure in (a), (b) lotus-type porous and (c), (d) nonporous NiAl rods. (a), (c) and (b), (d) show transverse and longitudinal cross sections, respectively. Figure 4-3. Compressive stress-strain curves of (a), (c), (e) nonporous NiAl and (b), (d), (f) lotus-type porous NiAl testing at (a), (b) 298 K, (c), (d) 673 K and (e), (f) 873 K Figure 4-4. Optical micrographs of exterior features of compressive specimens for (a), (c) nonporous NiAl and (b), (d) lotus-type porous NiAl after compression test at 673 K. Compressive direction is (a), (b) parallel and (c), (d) perpendicular to the solidification direction. Figure 4-5. Optical micrographs of exterior features of compressive specimens for (a), (c) nonporous NiAl and (b), (d) lotus-type porous NiAl after compression test at 873 K. Compressive direction is (a), (b) parallel and (c), (d) perpendicular to the solidification direction. Figure 4-6. Yield strength variation of nonporous and lotus-type porous NiAl with the solidification direction (a) parallel and (b) perpendicular to the compressive direction as a function of temperatureFigure 4-7. Optical micrographs of exterior features of porous specimen after compression test at (a), (c) 673 K and (b), (d) 873 K; compressive direction is (a), (c) parallel and (b), (d) perpendicular to the solidification direction. Figure 4-8. Scanning electron micrographs of specimen surfaces for lotus-type porous NiAl with the solidification direction (a) perpendicular and (b) parallel to the compressive direction after compression tests Figure 4-9. Schematic diagram of applied stress to (a) sharp and (b) blunt crack tips Figure 4-10. Scanning electron micrographs of parallel lotus-type porous specimen after compression test at (a) 298 K and (b) 673 K Figure 4-11. Scanning electron micrographs of (a) parallel and (b) perpendicular lotus-type porous specimen Figure 4-12. Inverse pole figure maps of nonporous specimens with the compressive direction (a) parallel and (b) perpendicular to the solidification direction Table 3-1. Chemical compositions of NiAl ingot, lotus-type porous and nonporous NiAl Table 3-2. Mechanical properties of lotus-type porous and nonporous NiAl with the solidification direction parallel and perpendicular to the compressive direction at room temperature Table 4-1. Mechanical properties of lotus-type porous and nonporous NiAl with the solidification direction parallel and perpendicular to the compressive direction at 298 K, 673 K and 873 K

151. 12. 4 2.1 4 2.1.1 4 2.1.2 11 2.1.3 14 2.2 Nickel Aluminide 17 2.2.1 -NiAl 19 2.2.2 223. NiAl 25 3.1 25 3.2 26 3.3 29 3.3.1 29 3.3.2 29 3.4 35 3.4.1 35 3.4.2 38 3.5 404. NiAl 42 4.1 42 4.2 43 4.3 44 4.3.1 44 4.3.2 47 4.4 54 4.4.1 54 4.4.2 59 4.5 655. 67 68Figure 2-1. Schematic diagram for an exterior view of lotus-type porous metal 5Figure 2-2. Temperature dependence of hydrogen solubility in solid and liquid of various metals under the hydrogen pressure of 0.1MPa 6Figure 2-3. Schematic diagram of pore nucleation and growth in unidirectional solidification in gas atmosphere 8Figure 2-4. Averaged pore diameter and porosity of lotus-type porous stainless steel under various pressure of mixed gases composed of (a) hydrogen and argon or (b) hydrogen and helium 10Figure 2-5. Schematic diagram of mold casting technique 12Figure 2-6. Schematic diagram for the melting part of continuous zone melting technique 13Figure 2-7. Schematic diagram of continuous casting apparatus 15Figure 2-8. Ultimate tensile strength and yield strength of lotus-type porous copper in the direction parallel and perpendicular to pore axis as a function of porosity 16Figure 2-9. Schematic diagram of compressive stress-strain curve of lotus-type porous metal 18Figure 2-10. Ni-Al phase diagram 20Figure 2-11. B2 crystal structure (space group Pmm, CsCl prototype) of NiAl 21Figure 2-12. Critical resolved shear stress for (a) a slip in 'soft' crystals, (b) a{112} and a{110}slip in 'hard' crystals 23Figure 3-1. Photograph of a universal testing machine 28Figure 3-2. Optical micrographs of pore morphology of lotus-type porous NiAl cross-sections (a) perpendicular and (b) parallel to the solidification direction 30Figure 3-3. X-ray diffraction patterns of lotus-type porous NiAl (a) before and (b) after homogenization heat treatment 31Figure 3-4. Compressive stress-strain curves of (a), (b) nonporous NiAl and (c), (d) lotus-type porous NiAl with the solidification direction (a), (c) parallel and (b), (d) perpendicular to the compressive direction 32Figure 3-5. Scanning electron micrographs of (a) lotus-type porous and (b) nonporous NiAl 36Figure 3-6. Scanning electron micrographs of crack tip blunting of lotus-type porous NiAl with the solidification direction (a) perpendicular and (b) parallel to the compressive direction 37Figure 3-7. Scanning electron micrographs of multi-crack for lotus-type porous NiAl. A magnified view of A and B in (a) is shown in (b) and (c), respectively. 39Figure 4-1. Photographs of (a) a universal testing machine and (b) a heating chamber near Jigs 45Figure 4-2. Optical micrographs of microstructure in (a), (b) lotus-type porous and (c), (d) nonporous NiAl rods. (a), (c) and (b), (d) show transverse and longitudinal cross sections, respectively. 46Figure 4-3. Compressive stress-strain curves of (a), (c), (e) nonporous NiAl and (b), (d), (f) lotus-type porous NiAl testing at (a), (b) 298 K, (c), (d) 673 K and (e), (f) 873 K 48Figure 4-4. Optical micrographs of exterior features of compressive specimens for (a), (c) nonporous NiAl and (b), (d) lotus-type porous NiAl after compression test at 673 K. Compressive direction is (a), (b) parallel and (c), (d) perpendicular to the solidification direction. 51Figure 4-5. Optical micrographs of exterior features of compressive specimens for (a), (c) nonporous NiAl and (b), (d) lotus-type porous NiAl after compression test at 873 K. Compressive direction is (a), (b) parallel and (c), (d) perpendicular to the solidification direction. 52Figure 4-6. Yield strength variation of nonporous and lotus-type porous NiAl with the solidification direction (a) parallel and (b) perpendicular to the compressive direction as a function of temperature 53Figure 4-7. Optical micrographs of exterior features of porous specimen after compression test at (a), (c) 673 K and (b), (d) 873 K; compressive direction is (a), (c) parallel and (b), (d) perpendicular to the solidification direction. 55Figure 4-8. Scanning electron micrographs of specimen surfaces for lotus-type porous NiAl with the solidification direction (a) perpendicular and (b) parallel to the compressive direction after compression tests 57Figure 4-9. Schematic diagram of applied stress to (a) sharp and (b) blunt crack tips 58Figure 4-10. Scanning electron micrographs of parallel lotus-type porous specimen after compression test at (a) 298 K and (b) 673 K 60Figure 4-11. Scanning electron micrographs of (a) parallel and (b) perpendicular lotus-type porous specimen 62Figure 4-12. Inverse pole figure maps of nonporous specimens with the compressive direction (a) parallel and (b) perpendicular to the solidification direction 64Table 3-1. Chemical compositions of NiAl ingot, lotus-type porous and nonporous NiAl 27Table 3-2. Mechanical properties of lotus-type porous and nonporous NiAl with the solidification direction parallel and perpendicular to the compressive direction at room temperature 34Table 4-1. Mechanical properties of lotus-type porous and nonporous NiAl with the solidification direction parallel and perpendicular to the compressive direction at 298 K, 673 K and 873 K 49