Creep Behavior of Nickel-Copper Solid Solution Alloys below 0. 55 T m
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I.D. CHOI, D.K. MATLOCK, and D.L. OLSON
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COMPRESSION IN PERGENT
Fig. 3 - - T h e elastic aftereffect in a compressed single crystal of brass;t2J 1 k g / m m 2 - 10 M N / m 2.
Substituting for e = 10 -3 and taking as trial value v = 1/3, b = 0.4 nm, we find n=2x-x 1 --
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0.4 x 10 -9 (m
1014 m -2
3 A dislocation density of l014 m -2 is typical of highly work-hardened metals and is many orders of magnitude higher than that observed by transmission electron microscopy of the crystals investigated here. We are, therefore, forced to seek an alternative explanation. A plausible mechanism is the elastic aftereffect, well known in deformation of single crystals of b r a s s , [2] where it is found that the stress v s strain curve obtained when the specimen is unloaded and then reloaded is not a singlevalued function but has the form shown in Figure 3. It is supposed that the contraction is entirely elastic when the specimen is first unloaded. As soon as the elastic forces in the regions that have undergone the most extensive plastic deformation are released, the remaining regions exert stresses on them of such size as to reverse the original deformation. These stresses increase as the unloading proceeds and cause a small amount of irreversible plastic flow. We attribute these stresses to the residual strains detected in Figures l(a) and 2(a).
The experimental work reported here was carried out in the Physics Department at the University of Bristol. The authors gratefully acknowledge Dr. D.J. Dingley's assistance with the technique of Kossel X-ray diffraction in the SEM. One of us (BC) was supported by a British Gas research grant. REFERENCES 1. R.E. Busch, R.T. Luedemann, and P.M. Gross: U.S. Dept. of Commerce Clearinghouse Report, AD-629 726, 1966, 53 pp. 2. G. Sachs and H. Shoji: Z . P h y s i k , 1927, vol. 45, pp. 776-96. METALLURGICAL TRANSACTIONS A
In two recent creep studies of inhomogeneous nickelcopper solid solution alloys, i . e . cast weld metal with solidification-induced composition gradients tll and nickelcopper laminate composites with controlled composition gradients across the layers, t2] the creep rates at an intermediate temperature (500 ~ were shown to decrease with an increase in homogenization. The creep behavior in inhomogeneous alloy systems reflects the composite effects of position-dependent creep properties as controlled by solid solution alloy content. To utilize composite modeling techniques in creep analyses of materials with composition gradients, creep data of homogeneous materials as a function of alloy content are required. Therefore, this study was undertaken to evaluate the creep behavior of nickel-copper solid solution alloys at intermediate temperatures and to provide a base set of data to evaluate the effect of gradients described above. 0'2] A series of 450 g ingots of nickel-copper solid solution alloys with various compositions was produced by melting nickel 270 (>99.97 pct) and copper C101 (>99.99
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