Chromium precipitation from β-Ni(Al, Ti) and γ'-Ni₃(Al, Ti) in the alloy (Ni₇₀Al₂₀Ti₁₀)_0.9Cr_0.1

Abstract

The crystallography and nucleation of the Cr phase (α) from both β-Ni(Al, Ti) and γ'-Ni₃(Al, Ti) in an α-β-γ' three-phase alloy are investigated using analytical electron microscopy. The α particles in β are spherically shaped and oriented parallel with the parent phase. Those in γ' are lath-shaped with a well-defined habit plane of (121)γ'/(312)α, a growth direction close to [111]α/[101]γ', and are related to γ' by the Kurdjumov-Sachs (K-S) orientation relationship. It is shown that α particles can nucleate only from the disordered γ phase which was stabilized at higher temperatures. The heterogeneous nucleation and distribution of α particles in γ' are interpreted in terms of a transformation sequence. Modification of the microstructure by rapid solidification is also discussed.