Elevated temperature compressive properties of Zr-modified NiAl
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I.
INTRODUCTION
ALTHOUGH the B2-ordered intermetallic NiA1 has a number of promising properties that make it an attractive replacement material for superalloys (i.e., high melting point, good thermal conductivity, moderate density, and excellent oxidation resistance), it has poor elevated-temperature strength and is seriously lacking in low-temperature tensile ductility and toughnessY m Simple third-element additions have been and are currently being investigated as a means to improve both of these deficiencies. For example, small (=_
2.2xl 0 -4
o
r
0
(D
2.2xl 0 -6
r
2.8xl 0-6
5O
y
2.2x10-3
E~1oo
2.8xl 0 -4
E
o o
Approximate strain rate, s -1
r
2.2xl 0-6
2.8x10-6
f
2.8~0 ~ f
0
I
I
I
2
4
6
2.2xl 0 -7
o
True compressive strain, %
I
I
2
4
6
True compressive strain, %
(a)
(a)
400
!
Approximate strain rate, s -1
600-
2.2x10-3
500
Approximate strain rate, s-1
.22
:~ 30o
.022
?_> === 2oo
= 300
2.2x10-4
o.
=e r
E
E
O O
|
8
o
200
2.2X10-3
S
9
10o
9J(10-4
2.2x10-6 100
1.7x10-6
?-2xl 0 -6 2.2x10-6
I 0
I
I
I
I
I
I
2 4 6 True compressive strain, %
8
2 4 6 True compressive strain, %
8
(c)
I
(a3
Fig. 4---True 1300 K compressive stress-strain curves as a function of strain rate for NiA1 alloys containing (a) 0.05Zr, (b) 0.1Zr, (c) 0.3Zr, and (d) 0.7Zr.
purposes, this stress jump did not result in any transient creep at the higher stress level. It appeared that this specimen was in steady state prior to and immediately following the stress increase. True compressive flow stress (tr)-strain rate (~)-temperature (T) behavior of the Zr-doped NiA1 alloys is presented in Figure 8, where.the flow stress was taken at 3 pet strain from the stress-strain diagrams (Figures 3 through 6) and from the steady-state regime of the creep curves (Figure 7). In addition to the present results, Figure 8(a) also contains some tensile test data (both constant-velocity and constantload creep data) from Bowman and Noebe t231 for the same lot of NiAI-0.05Zr. Comparison of the tensile and compressive results for the 0.05Zr composition reveal little, if any, dependency on the test method or stress direction. 2632--VOLUME 27A, SEPTEMBER 1996
Likewise, the constant-load compression creep results for 0.1Zr at 1200 K (Figure 8(b)) and the 1100 to 1400 K creep tests of 0.3Zr (Figure 8(c)) and 0.7Zr (Figure 8(d)) are consistent with the constant-velocity data. Utilizing Figure 8(a) as an example, the o--~-T properties appear to fall into three regimes: the fastest strain rate/lower temperature data follow a temperature-compensated exponential stress law (Eq. [1]); the slower strain rate/higher temperature data conform to a temperature-compensated power law (Eq. [2]); or, in some cases, the simpler constant-temperature version of Eq. [2].
(-Q/RT) (-Q/RT)
~} = A 9 exp (Co-) 9 exp
[1]
k = B 9 o-" 9 exp
[2]
METALLURGICAL AND MATERIALS TRANSACTIONS A
500 - -
0.7 Z r
150
y
.
~4oo - 0.3Zr
i
100 --0.1Zr
300
=
0.05 ~" 8 2o0
0.7 Zr 0.3 Zr
F
0.1 Zr
Y
n @
I--
100
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