Temperature Dependence of gamma/gamma-prime Lattice Parameter Misfit for Ni-base Superalloys
S.Yoshitake, T.Yokokawa, K.Ohno, H.Harada and M.Yamazaki
Published in
Proceedings of 5th Liege conference "Materials for Advanced Power Engineering 1994"
held in Liege, Belgium, October 3-6, 1994, pp.875-881(part I).
Abstract
The lattice parameters and volume fractions of the gamma and gamma-prime phases in four nickel-base superalloys have measured as a function of temperature using X-ray diffractometer. The X-ray profiles measured up to 1000(I_(BC were resolved using profile fitting method. The thermal expansion coefficient of gamma-prime phase was found to be smaller than that of gamma phase, so the gamma/gamma-prime lattice parameter misfit decreased as the temperature was raised. The higher creep rupture life is found to be associated with alloys in which the gamma-prime lattice parameter is less than that of gamma(i.e. negative misfit). A particular alloy, TMS63, which has negative misfit at all temperatures seem well suited for advanced turbine blade application. For some alloys, which have a simple chemistry, it was possible to use a statistical thermodynamic method(Cluster Variation Method) to asses the experimental data. The measured misfit data for high temperatures correlate well with calculations using the cluster variation method, whereas the measured volume fraction data shows less agreement with calculations.
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