Study of the Effect of Cold Deformation on the Structural-Phase State and Properties of Titanium Nickelide in Various Initial States

The effect of deforming samples of titanium nickelide (TiNi) using compression is examined for various initial states. The deformation results in changing the structural-phase state and the strength parameters. It is established that the cold compression deformation of bulk TiNi samples is feasible past the reference treatment at the different aging regimes resulting in a relative strain ε = 25%. It is revealed that the deformation behavior depends on the initial state, on the resulting structural-phase state, and on the properties of titanium nickelide. Cold deformation substantially increases the density of defects in the crystal lattice. The structures having the ultimate number of defects are obtained in samples before and after deformation aged for 1 and 5 h at 430°C. It is shown that irrespective of the initial structural state, the cold compression deformation partially suppresses both the forward and reverse martensitic transformations. Aging at 430°C for 1 and 5 h brings about an intensive precipitation of coherent Ti3Ni4 phase nanoparticles. The subsequent cold deformation with ε = 25% generates the strongest structure featuring the maximum hardness (up to 370 HV) and the highest deformation resistance (σ25% = 2185–2240 MPa).