Lattice Misfit of High Refractory Ruthenium Containing Nickel-Base Superalloys

Abstract

The influence of Ru, Co, Mo and W on the lattice misfit of eight highly alloyed Re containing single crystal nickel-base superalloys was investigated. High resolution X-ray diffraction (XRD) was used to relate the elemental partitioning behavior and the Vegard coefficients of the elements under investigation to the measured lattice parameter of the γ and γ′ phase. The residual chemical segregation and especially the coherency stress-induced tetragonal distortion of the γ matrix lattice in the high Mo containing alloys results in the observation of two different lattice parameters for the γ matrix phase. This leads to three overlapping, but clearly distinguishable {002} X-ray reflections.

Influence of rhenium and ruthenium on the local mechanical properties of the γ and γ′ phases in nickel-base superalloys

“…As the lattice parameters of both phases γ and γ′ are quite similar in nickel base superalloys, the (002) peaks of both phases overlap with each other. Therefore the detected (002) peak was deconvoluted into subpeaks to obtain the lattice parameter of γ and γ′ by fitting the measured (002) peak with Pseudo-Voigtfunctions, which are a combination of a Gaussian and a Lorentzian function [19]. The constrained lattice misfit δ of the alloys under investigation was derived from the lattice parameter a γ and a γ′ of the γ and γ′ phase using the following formula:…”