Lattice parameters and compositions of γ and γ′ during coarsening in the Ni-Al-Si system: A neutron powder diffraction study

Abstract

Ternary Ni-base alloys are often used as model systems for studying coarsening in multi-component systems. Ni-Al-Ti, Ni-Al-Mo, Ni-Cr-Si and more recently, Ni-Al-Si alloys have been used for such studies. These alloys allow the coherent precipitation of L1{sub 2} phase (Ni{sub 3}X, designated as {gamma}{prime}) from an F.C.C.-solid solution and thus enable the study of coarsening of precipitates in coherent systems. With the improvement in theoretical understanding of coarsening in multi-component systems, phase composition information (composition of precipitates and matrix) has become essential for proper interpretation of coarsening data obtained from ternary systems. However, such information is not readily available for many ternary systems, including the Ni-Al-Si system. The aim of this paper is two-fold: (1) To present the lattice parameters, temperature dependence of the lattice parameters, and compositions of {gamma} and {gamma}{prime} as a function of alloy composition in the Ni-Al-Si system. (2) To demonstrate the application of neutron powder diffraction and Rietveld analysis to samples that are not ideally suited for powder diffraction. This situation often occurs when powder diffraction techniques are used for engineering applications.