Severe plastic deformation of Ti74Nb26 shape memory alloys

Severe plastic deformation of Ti74Nb26 shape memory alloy was conducted successfully at room temperature using equal channel angular extrusion (ECAE). In conjunction with short post-extrusion heat treatments, ECAE improved the maximum transformation strain of the alloy from 1% to 1.7%. Moreover, it drastically reduced the irrecoverable strain during constant-stress thermal cycling experiments. After identical heat treatments, the specimens processed by one pass ECAE possess both higher transformation strain and higher irrecoverable strain as compared to those processed by four pass ECAE. However, the difference between the crystallographic texture contributions to the transformation strains of these specimens was minimal, and thus, the shape memory characteristics are believed to be influenced mainly by microstructural features. High dislocation density, small grain size, and precipitation of the omega phase were found to reduce not only the irrecoverable strain, but also the transformation strain.