Morphology of γ Precipitates in Ni-Rich γ'-Ni3 (Al,Ta)

Abstract

The microstrueture of a commercial nickel-base alloy normally consists of a coherent, cuboidal precipitate of γ’ (alloyed Ni3Al) in a matrix of γ (Ni solid solution). Recently, Ham et al., working with the ternary alloy 78Ni-l8Al-4Ti (a/o), have shown that by appropriate heat treatment a completely novel microstrueture can be developed, in which the matrix is γ’ and the precipitate is platelet γ. The present study represents an extension of this work, and reports some new findings on precipitation of γ in γ’ in alloys similar in composition to the Ni-Al-Ti alloy but with Ta replacing Ti.The alloys used were solutionized in the range 2200-2400°F and aged at l600°F for 24hrs (giving ∼ 10 vol. percent of γ in γ’). According to our most recent findings, unlike the binary system, the solubility of γ’ for γ reaches a maximum at ∼ 2200°F in these alloys.