Effect of C addition on mechanical properties of dual two-phase Ni3Al–Ni3V intermetallic alloys

Two kinds of dual two-phase intermetallic alloys containing Nb and Ti that are composed of geometrically close packed (GCP) Ni3Al (L12) and Ni3V (D022) structures were studied, focusing on the effect of C addition on microstructures and high-temperature tensile properties. The dual two-phase microstructures defined by primary Ni3Al precipitates and eutectoid region consisting of Ni3Al and Ni3V phases were dispersed by carbides at a majority of C contents. The positive temperature dependence of the flow strength was observed for all C-added alloys. The maximum strengthening took place at a C content below 0.5 at.%, irrespective of test temperatures. On the other hand, the tensile elongation rapidly increased with increasing C content, irrespective of test temperatures. Also, the C addition resulted in the change of the fracture mode from brittle transgranular fracture to ductile transgranular fracture in the low temperature range, and from brittle intergranular fracture to ductile transgranular fracture in the high temperature range. Possible mechanisms responsible for the strengthening and ductilization by the C addition were discussed, based on the behavior of solutes (such as C, V, Nb and Ti) and the carbides in the matrices, and also on the dual two-phase microstructure modified by the C addition.