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

摘要

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 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.