Evolution of Structural-Phase States in Ti Ni Surface Layers Synthesized by Electron Beam Treatment

The paper presents the results of X-ray diffraction analysis of nonequilibrium structural and elastic stress states in Ti Ni surface layers irradiated by low-energy electron beams. It is found that a surface layer with a mixed (2D columnar and 3D equi axial) sub microcrystalline structure is formed on the irradiated side of the Ti Ni specimens, and the volume fractions of the two structure types depend on the beam energy parameters and number of pulses. The B2 phase synthesized in the layer is characterized by lattice micro strain due to stresses of the first and second kinds (εI±1%, (εII=0.25%), and the layer as such is an internal stress concentrator for underlying layers of the material. In the intermediate layer beneath the stress concentrator, relaxation of irradiation-induced internal stress takes place. It is shown that the main mechanism of the relaxation is partial B2---B19' martensite transformation. The B19' martensite phase in the intermediate layer decreases the micro strain in the conjugate B2 phase. The thickness of the layer in which the relaxation processes develop through the B2---B19' martensite transformation is 10-15μm.