Microstructure, mechanical and functional properties of NiTi alloys processed by ECAP technique

Abstract
In recent years considerable attention has been focused on processing and investigation of NiTi alloys with ultrafine-grained (UFG) structure because they possess a combination of elevated mechanical and functional properties. Equal-channel angular pressing (ECAP) is the most interesting technique here as it allows avoiding pollution by impurities and obtaining bulk samples, that suitable for practical use. The aim of the given work is to systematically investigate the influence of regimes of ECAP on the microstructure, mechanical and functional properties of the NiTi alloys. It is shown that as a result of ECAP an equiaxed, homogeneous in volume, UFG structure with the grain size up to 200 nm is formed in the bulk rods (with the diameter 16-20 mm) of NiTi alloys. High strength (yield stress up to 1300 MPa) with enhanced functional properties (maximum recovery stress σ_r^max to 1100 MPa and maximum fully recoverable strain ε_r^max to 9.2%), which is considerably higher than in the coarsegrained state is achieved.