Effect of NbC addition on mechanical properties of dual two-phase Ni 3Al–Ni 3V intermetallic alloy

Abstract

Dual two-phase intermetallic alloy that has an alloy composition of Ni 75Al 9V 13Nb 3 and is composed of geometrically close packed (GCP) Ni 3Al (L1 2) and Ni 3V (D0 22) phases was studied, focusing on the effect of NbC addition on high-temperature tensile properties. The two-phase microstructures defined by primary Ni 3Al precipitates and eutectoid region consisting of Ni 3Al and Ni 3V phases were kept and were dispersed by Nb 2C particles regardless of NbC content. EPMA analysis showed that alloy compositions in matrix of the NbC added alloy were different from those in the base alloy. The positive temperature dependence of flow strength was observed for all NbC added alloys. In low temperature range the maximum strengthening took place at 1 at.% NbC content. On the other hand, tensile elongation increased with increasing NbC content up to 1 at.% NbC content and gradually decreased at NbC content over 1 at.% content in whole temperature ranges. Also, the NbC addition resulted in change of the fracture mode from brittle transgranular fracture to ductile transgranular fracture in low temperature range, and from brittle intergranular fracture to ductile transgranular in high temperature range. Possible mechanisms responsible for the strengthening and ductilization by NbC addition were discussed, based on the behavior of C solutes in the matrix, which were released from the charged NbC carbides.