Amorphization and its impact on nano-mechanical properties in martensitic Ti50Ni50 alloy

Deformation-induced amorphization (DIA) plays a crucial role in tailoring the mechanical and functional properties of TiNi shape memory alloys. However, the formation condition of amorphization under local shear deformation remain unclear. Here, we employ high-throughput nanoindentation to investigate the critical condition of DIA in a martensitic TiNi alloy and its impact on nanoscale mechanical properties. As indentation depth reaches 400 nm (equivalent strain 1.644), a distinct amorphous phase nucleates beneath the indenter. High-pressure torsion (HPT) experiments further reveal increased amorphous volume fraction with shear strain. The resulting DIA-TiNi alloy achieves a 90 % hardness gain over its as-cast crystalline counterpart and exhibits dramatically lower strain-rate sensitivity. Cooperative shear model analysis discloses an exceptional shear transformation zone volume (STZ) of 25.82 nm³, significantly surpassing that of melt-quenched metallic glasses. This cross-scale investigation defines the critical strain threshold and strain–amorphization relationship, guiding the design of amorphous–nanocrystalline TiNi alloys with enhanced stability and performance.