Microstructural refinement and enhanced mechanical properties of suction-cast NiTi-Al alloy for structural use

A significant refinement of the microstructure of structural NiTi alloy was achieved through a combination of Al addition and fabrication by suction casting. This is attributed to the change from a layer-by-layer to volume solidification mode with Al content increasing, which causes a change in grain shape from columnar to equiaxed. Furthermore, when compared with conventional casting, suction casting optimizes the microstructure of the alloy by refining the grain size and ensuring a homogeneous distribution of Ti₂Ni and Ni₂TiAl phases. The high cooling rate of suction casting also delays the formation of β′-Ni₂TiAl phase. Finally, this fine microstructure and uniform distribution of intermetallic phases result in the ultimate compressive strength of up to 2463.7 MPa, representing an improvement of 370 MPa over conventionally cast NiTi-Al alloy.