Tensile behavior of directionally solidified Ni₃Al intermetallics with different Al contents and solidification rates

Abstract

Despite the excellent high temperature mechanical properties of the Ni3Al intermetallic compound, its application is still limited due to its inherently weak grain boundary. Recent research advances have demonstrated that the tensile ductility can be enhanced by controlling the grain morphology using a directional solidification. In this study, a series of directional solidification experiments were carried out to increase both the tensile ductility and the strength of Ni₃Al alloys by arraying either the ductile phase of γ-Ni-rich dendrite fibers or the hard phase of β-NiAl dendrite fibers in the γ′-Ni₃Al matrix. The dendrite arm spacing could be controlled by the solidification rate, and the volume fraction of the γ or β phase could be altered by the Al content, ranging from 23 at.% to 27 at.%. With an increasing Al content, the γ dendritic microstructure was transformed into the β dendrite in the γ′ matrix, thereby reducing the tensile ductility by increasing the volume fraction of brittle β dendrites in the γ′ matrix. With an increasing solidification rate, the dendrite arm spacing decreased and the tensile properties of Ni₃Al varied in a complex manner. The microstructural evolution affecting the tensile behavior of directionally solidified Ni₃Al alloy specimens with different solidification rates and Al contents is discussed.