An investigation of thermal aging effects on the mechanical properties of a Ni3Al-based alloy by nanoindentation

Ni₃Al-based intermetallic alloys are composed of a γ network and γ′ domains. In general, through precipitation, the γ′ phase is used as a hardening source for this alloy. This study examined how γ′ acts as a hardening material in a cast Ni₃Al-based intermetallic alloy. Specimens cut from a centrifugally cast tube were aged in Ar at elevated temperatures for up to 1600 h. Hardness tests were then performed in air at room temperature. Vickers microhardness and nanoindentation tests were carried out on specimens aged at 900 °C and 1100 °C. The microstructures were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The microhardness of bulk Ni₃Al decreased dramatically with increasing thermal aging time at 900 °C, but the nanohardness measured by the nanoindenter did not significantly decrease. The nanohardness data suggested that the hardening effects were caused by the precipitation of the γ′ phase on the γ and γ′ cells.