- Email: [email protected]
Microstructure and mechanical properties of NiAl intermetallic compound synthesized by reactive sintering under pressure
Journal of
Materials Processing Technology ELSEVIER
Journal of Materials Processing Technology 63 (1997) 298-302
Microstructure and Mechanical Properties of NiAI Intermetall ic Compound Synthesized by Reactive Sintering under Pressure Kiyotaka MATSUURA', Toshiki KITAMUTRA b and Masayuki KUDOH'
b
, Division of Materials Science and Engineering, Graduate School of Engineering, Hokkaido University, Sapporo, Hokkaido, 060 Japan. Graduate student, Graduate School of Engineering, Hokkaido University.
Abstract
Reactive sintering of a nickel-aluminum mixed powder compact is performed under several levels of pressure up to 360 MPa at several temperatures up to an eutectic temperature of 913 K. When the sintering temperature is below 748 K, intermetallic compounds are formed at the interface between the two metals, and they grow slowly during sintering. When the temperature of the compact is slowly elevated above 900 K, the temperature suddenly goes up to about 1900 K in a very short time, owing to the exothermic reaction of a combustion synthesis of mono-nickel aluminide (NiAI). As the pressure which was applied during sintering increases, the porosity of the compacts decreases, and the density and hardness increase. Keywords: powder metallurgy, reactive sintering, combustion synthesis, intermetallic compound, nickel aluminide, mechanical properties
1. Introduction
Intermetallic compounds in the Ni-AI system such as Ni 3AI and NiAI are promising potential high temperature materials which may take the place of conventional nickel-base superalloys. Tri -nickel aluminide Ni 3AI demonstrates extraordinary properties, such as a high melting point, positive dependence of strength on temperature, good resistance to creep and oxidation, and relatively low density [1-3J. On the other hand, mono-nickel aluminide NiAI receives much attention due to its higher melting point, lower densi ty, and better oxidation resistance than Ni3AI [4, 5J. The excellent properties of these nickel aluminides make them attractive for aerospace and structural applications at elevated temperatures. However, the most significant disadvantage of these nickel aluminides is brittleness at room temperature, although the brittleness of Ni3AI is improved to some degree by microalloying with boron [6J and that of NiAl by grain refinement [7, 8J. One possible solution to this problem is utilization of 0924-0136/97/$15.00 © 1997 Elsevier Science SA All rights reserved
PI! S0924-0136(96)02639-8
the near-net-shape fabrication technique such as powder metallurgy processing. Reactive sintering [9-14J of mixed powder compact is one of the novel and attractive processes. The present study investigates how the pressure applied during the reactive sintering of Ni-AI mixed powder compacts affects the microstructure and mechanical properties. 2. Exper imental procedure
Carbonyl nickel powder (99.8 % pure, 4 to 7 f.J. m in diameter) and gas-atomized aluminum powder (99.8 % pure, 40 to 150 f.J. m in diameter) were mixed in an atomic proportion of 1:1 with the addition of a small amount of ethanol. The powder mixture was cold-pressed into cylindrical green compacts in a metal mold up to the maximum compacting pressure of 1400 MPa. The diameter and height of the compacts were 16 mm and 12 mm, respectively. The compacts were sintered in air under several levels of pressure up to 360 MPa at several temperatures up to an eutectic temperature of 913 K.
K Matsuura et aL / Journal of Materials Processing Technology 63 (1997) 298-302
299
The pressure was applied by using a pseudo-HIP (pseudo-Hot-Isostatic-Pressing) process [15J. The microstructure of the sintered compact was observed. and the density. hardness and ductility of the compact were measured at room temperature. The density was evaluated by Archimedes' method. the hardness by a Vickers hardness tester and the ductility by the critical rolling reduction which was defined as the value of the rolling reduction at which cracks which initiated at the side edge propagated to a quarter width of the rolled compact. The initial thickness of the rolled compact was 6 mm and the reduction per pass was o. 25 mm.
a
Results and Discussion
Fig.2 Microstructure of the green compact. 3. 1. Green compact
Figure 1 shows the effects of compacting pressure on the densi ty of the green compact. As the pressure is increased. the density gradually increases towards the ideal density of 5.17 Mg/m 3 • Because the density after pressing to the maximum of 1400 MPa is 5.01 Mg/m 3 • the final volume fraction of the pores remaining in the green compact is calculated to be no more than 3 %. according to Eq. (1) [IB]. p = PM'
x(
P N' J!A 1+ P AI 161 i)/ { P AI P N' (lIA l + J61,)}
(1)
where P and 11 are the density and atomic weight of the material indicated by the subscript. Figure 2 shows the microstructure on a section perpendicular to the compression axis of the cylindrical green compact. Aluminum powder particles are dispersed homogeneously in the matrix phase of nickel. Very small pores are observed in the matrix phase.
.
, ....... '"'I 0
,, ,, o , ,, ,, ,, , ,, , , , ,o'" , , , ,",
-
6 Ideal Green Compact Density
_e-e-e e-e
/
~e
'g2R
--AI . Ni
c
0000°0
o
_e-e-
0, 00 0.,
0
0
Ni 2AI 3
~ 50
-
e--_
c Q) u c
. . ,, o
o
() ,
Ie
. ..'
i'Io.........~/:
I
500
1000
1500
Pressure (MPa) Fig. 1 Effects of compacting pressure on the density of the green compact.
;1-
0
-_ ............... -
0 0
0
.
'
0
.
0
11\)
0
'~
...... '
.
oJ
,,
,
, ,, ,, ,
0
0
0
,
0
, , ,
0
1\"
, .. J'
,
~Ni3AI
'0
~.\:
0 0
kNiAI
,'.
..
0
•
o ----------,~. o 10
3
o
, .........
:'
.
0 0
20
30
Distance (f1 ill) Fig.3 Microstructure of the compact sintered at 723 K for 160 ks without pressure (a). and EPMA line analysis (b).
K. Matsuura et a1. / Journal of Materials Processing Technology 63 (1997) 298.302
300
3. 2. Low tempe ratu re s i nte r i n9
Figure 3(a) shows the microstructure of a sintered compact. Intermetallic phases are formed at the interface between aluminum and nickel phases Small pores are observed at the interface between intermetallic phases and aluminum particles and also inside the intermetallic phases. The formation of these pores is explained to be caused by the Kirkendall effect [17J. Figure 3(b) shows the results of EPMA analysis performed on the white line shown in Fig. 3(a). The results shown in Figs. 3(a) and 3(b) can be summarized as follows: (1) particles of NiAl a phase are formed in aluminum phase. (2) a thick rim of Ni.Al a phase surrounds the NiAla-aluminum mixed region, (3) very thin layers of NiAl and NiaAl phases surround the rim of Ni.Al a phase, and (4) relatively thick films of a nickel oxide phase are formed at the interface between nickel powder particles. Figure 4 shows the change in the ductility of the compact evaluated by the critical rolling reduction. It is impossible to roll the green compact. However, after sintering for 10 to 20 ks, a very high critical rolling reduction is measured. The maximum critical rolling reduction reaches 95 %, when the sintering temperature is 723 K. The increase in the ductility of the compact is considered to be caused by the diffusion junction between powder particles, while the decrease observed for the oversintered compact is explained by the formation of hard intermetallic compound phases at the interface between nickel and aluminum.
100
---
l:::.
to
2R
0\
c
/I
0 :;::;
::::J '0 Q)
0)
DO
~
()
a: c
ctl
:;::;
\
0
0& \ \
.;::
Sintering Temp. o 748 K l:::. 723 K o 698 K
6
~
'ecn o
Q)
3
o
100
200
300
Sintering Time (ks) Fig.5 Change in density of the compact during sintering without pressure.
0
50
"'6 a: ()
Sintering Temp. 0748 K l:::. 723 K 0698 K
Figure 5 shows the change in density of the compact during sintering. The density slowly decreases as time passes. When the sintering temperature is elevated from 698 K to 723 K, the density decreases remarkably. However. when the temperature is elevated further to 748 K, the decrements in density become less remarkable and after approximately 300 ks at this temperature, the' density begins to increase. As the sintering proceeds, both pores and the intermetallic phases grow, as shown in Fig. 6. The growth of pores leads to a decrease in density of the compact, while that of intermetallic phases leads to a density increase, according to Vegard's law. The results in Fig. 5 suggest that at low temperatures, the growth rate of pores is higher than that of intermetallic phases, but at high temperatures, the values of their growth rates are reversed.
~
0
~0
o" L0..i6.-l:::.- LSC:J:::-....-!::. 0 100
200
~o
300
Sintering Time (ks) Fig.4 Change in the ductility of the compact during sintering without pressure.
Fig.6 Microstructure of the compact sintered at 748 K for 43 ks without pressure.
K. Matsuura et al. / Journal of Materials Processing Technology 63 (1997) 298-302
The formation of pores damages the mechanical properties of the sintered materials. To avoid the formation of pores, we applied pressure to the compact during sintering. Figure 7 shows the effects of the sintering pressure on the density of the compact. The density increases with increasing pressure. The effects are particularly remarkable in the low pressure region. The increase in density is caused by the decrease of the pores, as shown in Fig. 8.
301
3.3. High temperature sintering
Figure 9 shows the change in the temperature of the compact during a high temperature sintering. When the temperature was elevated to approximately an eutectic temperature at a rate of 2 K/s, a sudden generation of heat was observed. Figure 10 shows the microstructure of the high temperature sintered compact. An electron probe microanalysis indicated that this compact is composed of mononickel aluminide with a composition which is almost stoichiometric. Therefore, the heat generation observed in Fig. 9 is caused by the exothermic reaction of a combustion synthesis of NiAl from the mixture of nickel and aluminum powders.
5 M
E
""--
fI
0)
~
Z.
'ec::n
Sintering Temp.
--
• 783 K o 748 K
n1 .... (])
300
~
(])
0 4 .5
o
100
200
Pressure (MPa) Fig.7 Effects of the sintering pressure on the density of the compact. Sintering time: 43ks.
S2' ....(]) 1500f-::J
c.. E (])
1000 I
400
450
500
Time (s) Fig.9 Change in the temperature of the compact during a high temperature sintering with pressure of 37 MPa.
Fig.8 Microstructure of the compact sintered at 748 K for 43 ks with pressure of 240 MPa.
Fig.l0 Microstructure of the high temperature sintered compact. Sintering pressure: 265 MPa. Sintering time: 0.6 ks.
302
K. Matsuura et al.!Journal of Materials Processing Technology 63 (1997) 298-302
Figures 11 and 12 show the effects of the sintering pressure on the density and hardness of NiAI, respectively. As the pressure increases, the density and hardness increase.
6
./. .. .. . Ideal Density of NiAI
----------Ir------Ir--------·--------·-~-----
1 OJ
/
5 •
6
------
----------
/
>-
•
+-'
'(j)
c
~4
4. Conc I us ions
We performed a high-pressure reactive sintering of a nickel-aluminum mixed powder compact, and obtained the following conclusions. (1) When the sintering temperature is below 748 K, the ductility of the compact dramatically increases in a short time. A sintering for a long time, however, results in the formation of intermetallic phases and pores. The former leads to the increase in density and hardness of the compact, while the latter the decrease. Applying pressure during the sintering leads to a dramatic increase in the density and hardness of the compact. (2) When the sintering temperature is elevated above 900 K, NiAI with uniform structure is· produced by a combustion synthesis from the powder mixture. Applying pseudo-HI Ping pressure during the combustion synthesis leads to a dramatic increase in the density and hardness of the compact. References
100
200
300
Pressure (MPa) Fig. 11 Effects of the sintering pressure on the density of NiAI. Sintering time: 0.6 ks.
350
•
• •
150 0;------'----:1-=-0-=-0---'--------=-20~0,....----'---3::-:'00
Pressure (MPa) Fig. 12 Effects of the sintering pressure on the hardness of NiAI. Sintering time: 0.6 ks.
[lJ N.S.Stoloff, Int. Met. Rev. , 29(984) 123. [2J D. P. Pope and S. S. Ezz, Int. Met. Rev., 29( 1984), 136. [3J 1. Wolfenstine, H. K. Kim, and 1. C. Earthman, Metall.Mat. Trans. A, 25A(1994) 2477. [4J T.Suzuki and H. Hosoda. Intermetallic Compounds, lpn. Inst. Met., (990) 13. [5J I.G.Lee, A.K.Ghosh, R.Ray, and S. lha, Metall. Mat. Trans. A, 25A(1994) 2017. [6J C. T. Liu and 1. O. Steigler, Science, 226(984) 636. [7J E. M. Schulson, Res. Mech. Lett., 1(981) 111. [8J E.M.Schulson and D.R.Barker, Scripta Metall., 17(983) 519. [9J D.M.Sims, A.Bose and R.M.German, Prog.Powder Metall. 43(987) 575. [lOJ A. Bose, B. H. Rabin and R. M. German, Powder Metall. Int., 20(988) 25. [l1J I. Song and N.N.Thadhani, Metall. Trans. A. 23A(992) 41. [12J J.P.Lebrat, A. Varma, and A.E. Miller, Metall. Trans. A, 23A(992) 69. [l3J C. Nishimura and C. T. Liu, Acta Metall. Mater. 41(993) 113. [14 J W. C. Chiou and C. T. Hu, Metall. Ma t. Trans. A, 25A(994) 985. [l5J B. L. Ferguson, Int. 1. Powder Metallurgy and Powder Technology, 21(1985) 201. [l6J K. Matsuura, T.Ohmi, Y. I toh, M. Kudoh and D. Tanaka, 1. lpn. Inst. Light Met., 45(995) 144. [17J F.Aldinger, Acta Metall., 22(1974) 923.
Materials Processing Technology ELSEVIER
Journal of Materials Processing Technology 63 (1997) 298-302
Microstructure and Mechanical Properties of NiAI Intermetall ic Compound Synthesized by Reactive Sintering under Pressure Kiyotaka MATSUURA', Toshiki KITAMUTRA b and Masayuki KUDOH'
b
, Division of Materials Science and Engineering, Graduate School of Engineering, Hokkaido University, Sapporo, Hokkaido, 060 Japan. Graduate student, Graduate School of Engineering, Hokkaido University.
Abstract
Reactive sintering of a nickel-aluminum mixed powder compact is performed under several levels of pressure up to 360 MPa at several temperatures up to an eutectic temperature of 913 K. When the sintering temperature is below 748 K, intermetallic compounds are formed at the interface between the two metals, and they grow slowly during sintering. When the temperature of the compact is slowly elevated above 900 K, the temperature suddenly goes up to about 1900 K in a very short time, owing to the exothermic reaction of a combustion synthesis of mono-nickel aluminide (NiAI). As the pressure which was applied during sintering increases, the porosity of the compacts decreases, and the density and hardness increase. Keywords: powder metallurgy, reactive sintering, combustion synthesis, intermetallic compound, nickel aluminide, mechanical properties
1. Introduction
Intermetallic compounds in the Ni-AI system such as Ni 3AI and NiAI are promising potential high temperature materials which may take the place of conventional nickel-base superalloys. Tri -nickel aluminide Ni 3AI demonstrates extraordinary properties, such as a high melting point, positive dependence of strength on temperature, good resistance to creep and oxidation, and relatively low density [1-3J. On the other hand, mono-nickel aluminide NiAI receives much attention due to its higher melting point, lower densi ty, and better oxidation resistance than Ni3AI [4, 5J. The excellent properties of these nickel aluminides make them attractive for aerospace and structural applications at elevated temperatures. However, the most significant disadvantage of these nickel aluminides is brittleness at room temperature, although the brittleness of Ni3AI is improved to some degree by microalloying with boron [6J and that of NiAl by grain refinement [7, 8J. One possible solution to this problem is utilization of 0924-0136/97/$15.00 © 1997 Elsevier Science SA All rights reserved
PI! S0924-0136(96)02639-8
the near-net-shape fabrication technique such as powder metallurgy processing. Reactive sintering [9-14J of mixed powder compact is one of the novel and attractive processes. The present study investigates how the pressure applied during the reactive sintering of Ni-AI mixed powder compacts affects the microstructure and mechanical properties. 2. Exper imental procedure
Carbonyl nickel powder (99.8 % pure, 4 to 7 f.J. m in diameter) and gas-atomized aluminum powder (99.8 % pure, 40 to 150 f.J. m in diameter) were mixed in an atomic proportion of 1:1 with the addition of a small amount of ethanol. The powder mixture was cold-pressed into cylindrical green compacts in a metal mold up to the maximum compacting pressure of 1400 MPa. The diameter and height of the compacts were 16 mm and 12 mm, respectively. The compacts were sintered in air under several levels of pressure up to 360 MPa at several temperatures up to an eutectic temperature of 913 K.
K Matsuura et aL / Journal of Materials Processing Technology 63 (1997) 298-302
299
The pressure was applied by using a pseudo-HIP (pseudo-Hot-Isostatic-Pressing) process [15J. The microstructure of the sintered compact was observed. and the density. hardness and ductility of the compact were measured at room temperature. The density was evaluated by Archimedes' method. the hardness by a Vickers hardness tester and the ductility by the critical rolling reduction which was defined as the value of the rolling reduction at which cracks which initiated at the side edge propagated to a quarter width of the rolled compact. The initial thickness of the rolled compact was 6 mm and the reduction per pass was o. 25 mm.
a
Results and Discussion
Fig.2 Microstructure of the green compact. 3. 1. Green compact
Figure 1 shows the effects of compacting pressure on the densi ty of the green compact. As the pressure is increased. the density gradually increases towards the ideal density of 5.17 Mg/m 3 • Because the density after pressing to the maximum of 1400 MPa is 5.01 Mg/m 3 • the final volume fraction of the pores remaining in the green compact is calculated to be no more than 3 %. according to Eq. (1) [IB]. p = PM'
x(
P N' J!A 1+ P AI 161 i)/ { P AI P N' (lIA l + J61,)}
(1)
where P and 11 are the density and atomic weight of the material indicated by the subscript. Figure 2 shows the microstructure on a section perpendicular to the compression axis of the cylindrical green compact. Aluminum powder particles are dispersed homogeneously in the matrix phase of nickel. Very small pores are observed in the matrix phase.
.
, ....... '"'I 0
,, ,, o , ,, ,, ,, , ,, , , , ,o'" , , , ,",
-
6 Ideal Green Compact Density
_e-e-e e-e
/
~e
'g2R
--AI . Ni
c
0000°0
o
_e-e-
0, 00 0.,
0
0
Ni 2AI 3
~ 50
-
e--_
c Q) u c
. . ,, o
o
() ,
Ie
. ..'
i'Io.........~/:
I
500
1000
1500
Pressure (MPa) Fig. 1 Effects of compacting pressure on the density of the green compact.
;1-
0
-_ ............... -
0 0
0
.
'
0
.
0
11\)
0
'~
...... '
.
oJ
,,
,
, ,, ,, ,
0
0
0
,
0
, , ,
0
1\"
, .. J'
,
~Ni3AI
'0
~.\:
0 0
kNiAI
,'.
..
0
•
o ----------,~. o 10
3
o
, .........
:'
.
0 0
20
30
Distance (f1 ill) Fig.3 Microstructure of the compact sintered at 723 K for 160 ks without pressure (a). and EPMA line analysis (b).
K. Matsuura et a1. / Journal of Materials Processing Technology 63 (1997) 298.302
300
3. 2. Low tempe ratu re s i nte r i n9
Figure 3(a) shows the microstructure of a sintered compact. Intermetallic phases are formed at the interface between aluminum and nickel phases Small pores are observed at the interface between intermetallic phases and aluminum particles and also inside the intermetallic phases. The formation of these pores is explained to be caused by the Kirkendall effect [17J. Figure 3(b) shows the results of EPMA analysis performed on the white line shown in Fig. 3(a). The results shown in Figs. 3(a) and 3(b) can be summarized as follows: (1) particles of NiAl a phase are formed in aluminum phase. (2) a thick rim of Ni.Al a phase surrounds the NiAla-aluminum mixed region, (3) very thin layers of NiAl and NiaAl phases surround the rim of Ni.Al a phase, and (4) relatively thick films of a nickel oxide phase are formed at the interface between nickel powder particles. Figure 4 shows the change in the ductility of the compact evaluated by the critical rolling reduction. It is impossible to roll the green compact. However, after sintering for 10 to 20 ks, a very high critical rolling reduction is measured. The maximum critical rolling reduction reaches 95 %, when the sintering temperature is 723 K. The increase in the ductility of the compact is considered to be caused by the diffusion junction between powder particles, while the decrease observed for the oversintered compact is explained by the formation of hard intermetallic compound phases at the interface between nickel and aluminum.
100
---
l:::.
to
2R
0\
c
/I
0 :;::;
::::J '0 Q)
0)
DO
~
()
a: c
ctl
:;::;
\
0
0& \ \
.;::
Sintering Temp. o 748 K l:::. 723 K o 698 K
6
~
'ecn o
Q)
3
o
100
200
300
Sintering Time (ks) Fig.5 Change in density of the compact during sintering without pressure.
0
50
"'6 a: ()
Sintering Temp. 0748 K l:::. 723 K 0698 K
Figure 5 shows the change in density of the compact during sintering. The density slowly decreases as time passes. When the sintering temperature is elevated from 698 K to 723 K, the density decreases remarkably. However. when the temperature is elevated further to 748 K, the decrements in density become less remarkable and after approximately 300 ks at this temperature, the' density begins to increase. As the sintering proceeds, both pores and the intermetallic phases grow, as shown in Fig. 6. The growth of pores leads to a decrease in density of the compact, while that of intermetallic phases leads to a density increase, according to Vegard's law. The results in Fig. 5 suggest that at low temperatures, the growth rate of pores is higher than that of intermetallic phases, but at high temperatures, the values of their growth rates are reversed.
~
0
~0
o" L0..i6.-l:::.- LSC:J:::-....-!::. 0 100
200
~o
300
Sintering Time (ks) Fig.4 Change in the ductility of the compact during sintering without pressure.
Fig.6 Microstructure of the compact sintered at 748 K for 43 ks without pressure.
K. Matsuura et al. / Journal of Materials Processing Technology 63 (1997) 298-302
The formation of pores damages the mechanical properties of the sintered materials. To avoid the formation of pores, we applied pressure to the compact during sintering. Figure 7 shows the effects of the sintering pressure on the density of the compact. The density increases with increasing pressure. The effects are particularly remarkable in the low pressure region. The increase in density is caused by the decrease of the pores, as shown in Fig. 8.
301
3.3. High temperature sintering
Figure 9 shows the change in the temperature of the compact during a high temperature sintering. When the temperature was elevated to approximately an eutectic temperature at a rate of 2 K/s, a sudden generation of heat was observed. Figure 10 shows the microstructure of the high temperature sintered compact. An electron probe microanalysis indicated that this compact is composed of mononickel aluminide with a composition which is almost stoichiometric. Therefore, the heat generation observed in Fig. 9 is caused by the exothermic reaction of a combustion synthesis of NiAl from the mixture of nickel and aluminum powders.
5 M
E
""--
fI
0)
~
Z.
'ec::n
Sintering Temp.
--
• 783 K o 748 K
n1 .... (])
300
~
(])
0 4 .5
o
100
200
Pressure (MPa) Fig.7 Effects of the sintering pressure on the density of the compact. Sintering time: 43ks.
S2' ....(]) 1500f-::J
c.. E (])
1000 I
400
450
500
Time (s) Fig.9 Change in the temperature of the compact during a high temperature sintering with pressure of 37 MPa.
Fig.8 Microstructure of the compact sintered at 748 K for 43 ks with pressure of 240 MPa.
Fig.l0 Microstructure of the high temperature sintered compact. Sintering pressure: 265 MPa. Sintering time: 0.6 ks.
302
K. Matsuura et al.!Journal of Materials Processing Technology 63 (1997) 298-302
Figures 11 and 12 show the effects of the sintering pressure on the density and hardness of NiAI, respectively. As the pressure increases, the density and hardness increase.
6
./. .. .. . Ideal Density of NiAI
----------Ir------Ir--------·--------·-~-----
1 OJ
/
5 •
6
------
----------
/
>-
•
+-'
'(j)
c
~4
4. Conc I us ions
We performed a high-pressure reactive sintering of a nickel-aluminum mixed powder compact, and obtained the following conclusions. (1) When the sintering temperature is below 748 K, the ductility of the compact dramatically increases in a short time. A sintering for a long time, however, results in the formation of intermetallic phases and pores. The former leads to the increase in density and hardness of the compact, while the latter the decrease. Applying pressure during the sintering leads to a dramatic increase in the density and hardness of the compact. (2) When the sintering temperature is elevated above 900 K, NiAI with uniform structure is· produced by a combustion synthesis from the powder mixture. Applying pseudo-HI Ping pressure during the combustion synthesis leads to a dramatic increase in the density and hardness of the compact. References
100
200
300
Pressure (MPa) Fig. 11 Effects of the sintering pressure on the density of NiAI. Sintering time: 0.6 ks.
350
•
• •
150 0;------'----:1-=-0-=-0---'--------=-20~0,....----'---3::-:'00
Pressure (MPa) Fig. 12 Effects of the sintering pressure on the hardness of NiAI. Sintering time: 0.6 ks.
[lJ N.S.Stoloff, Int. Met. Rev. , 29(984) 123. [2J D. P. Pope and S. S. Ezz, Int. Met. Rev., 29( 1984), 136. [3J 1. Wolfenstine, H. K. Kim, and 1. C. Earthman, Metall.Mat. Trans. A, 25A(1994) 2477. [4J T.Suzuki and H. Hosoda. Intermetallic Compounds, lpn. Inst. Met., (990) 13. [5J I.G.Lee, A.K.Ghosh, R.Ray, and S. lha, Metall. Mat. Trans. A, 25A(1994) 2017. [6J C. T. Liu and 1. O. Steigler, Science, 226(984) 636. [7J E. M. Schulson, Res. Mech. Lett., 1(981) 111. [8J E.M.Schulson and D.R.Barker, Scripta Metall., 17(983) 519. [9J D.M.Sims, A.Bose and R.M.German, Prog.Powder Metall. 43(987) 575. [lOJ A. Bose, B. H. Rabin and R. M. German, Powder Metall. Int., 20(988) 25. [l1J I. Song and N.N.Thadhani, Metall. Trans. A. 23A(992) 41. [12J J.P.Lebrat, A. Varma, and A.E. Miller, Metall. Trans. A, 23A(992) 69. [l3J C. Nishimura and C. T. Liu, Acta Metall. Mater. 41(993) 113. [14 J W. C. Chiou and C. T. Hu, Metall. Ma t. Trans. A, 25A(994) 985. [l5J B. L. Ferguson, Int. 1. Powder Metallurgy and Powder Technology, 21(1985) 201. [l6J K. Matsuura, T.Ohmi, Y. I toh, M. Kudoh and D. Tanaka, 1. lpn. Inst. Light Met., 45(995) 144. [17J F.Aldinger, Acta Metall., 22(1974) 923.