The Influence of Warm Deformation on the Structure and Martensitic Transformations in TiNi-Based Alloys

The regularities of microstructure formation in binary TiNi alloys with a Ni content of 50.2 and 50.8 at.% under warm abc pressing and isothermal (723 K) multipass caliber rolling had been studied. Microstructure composed of submicrocrystalline grains and subgrains was found after final abc pressing at 723 K with a total true strain e = 8.44. Three stages of grain structure evolution were revealed in the TiNi alloy with 50.8 at.% Ni subjected to warm rolling. At the first stage with low strains, the average grain size < d > increased due to collective dynamic recrystallization. The average grain size < d > decreased steeply due to discontinuous and continuous dynamic recrystallization at the second and third rolling stage. Microstructure composed of micro-and submicrocrystalline grains was observed after rolling with e = 2.0. The sequences and temperatures of martensite transformations from a cubic B2 phase to rhombohedral R and monoclinic B19' martensite phases were studied in depend on the strain accumulated by samples under abc pressing and rolling.