Effect of directional growth-rate on the mechanical properties of Ni3Al

Polycrystalline Ni3Al were grown unidirectionally at various growth rates using a floating zone method. The as-grown alloys were heat-treated just below solidification temperature. Room-temperature tensile properties of the as-grown and heat-treated alloys were examined and the cause of the growth-rate dependence of the mechanical properties in the as-grown alloys was studied. Yield stress and work-hardening rate decreased and tensile elongation increased by the heat treatment. The heat-treated alloys fractured transgranularly similar to the as-grown single-phase Ni3Al. This proves that the major cause of the growth rate dependence of the mechanical properties is the presence of the NiAl in the Ni3Al matrix. The growth rate dependence on the ductility still remained in the heat-treated alloys. This suggests that the bulk Ni3Al properties are dependent on the growth rate.