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 Ti2 Ni and Ni_(2)TiAl phases.The high cooling rate of suction casting also delays the formation ofβ'-Ni_(2)TiAl 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.