Structure and Phase Transformations in TiNiFe Ternary Alloys Subjected to Plastic Deformation by High-Pressure Torsion and Subsequent Heat Treatment

摘要

The results of a complex study of ternary TiNiFe alloys with a low-temperature shape-memory effect subjected to megaplastic deformation by high-pressure torsion (HPT) with subsequent heat treatment are presented. Investigations have been performed using X-ray diffraction, transmission and scanning elec tron microscopy, and measurements of electrical properties. It has been established that, at moderate degrees of reduction, the plastic deformation in the Ti_(50)Ni_(49)Fe_1 alloy induces a B2<-> 519' thermoelastic martensitic transformation and the formation of a developed banded dislocation and twin structure in the 519' marten-site; in the Ti_(50)Ni_(47)Fe_ alloy, a mainly analogous dislocation substructure is formed, but in the B2 austenite. The megaplastic deformation by HPT at room temperature leads to the amorphization of the Ti_(50)Ni_(49)Fe_1 alloy and to the high-angle nanofragmentation of the Ti_(50)Ni_(47)Fe_3 alloy. Specific features of the evolution of the structure and martensitic transformations in the TiNiFe ternary alloys after plastic deformation and heat treatment have been established. It has been found that the heat treatment of both alloys after HPT at tem peratures of 553-773 K results in the formation of a nanocrystalline or mixed nano-submicro-crystalline structure.