Patterns of change of normal and tangential components of the internal stresses, induced in the near-surface layer of tini by electron beam treatment

The structural and phase state, the distribution of lattice distortion in the surface layers (15 microns long) of TiNi alloy modified by high-current low-energy electron beams has been investigated using the $X$-ray diffraction technique. Three thin surface layers following one after another with different type of crystalline structure were revealed. It is discovered that on the irradiated side of the specimen of TiNi is always formed the surface layer with the columnar structure on the basis of B2-phase. Synthesized in the layer B2-phase is characterized by the microstrain of the lattice, caused by stresses $(\varepsilon^\mathrm I\approx\pm1$ %, $\varepsilon^\mathrm{II}=0.25$ %), and layer itself is the concentrator of internal stresses for the under layers of material. In the interlayer located under it the process of relaxation of internal stresses, induced by irradiation, is developed. It is shown that the basic mechanism of this relaxation is partial deformation martensite transformation of $\mathrm B2\to\mathrm B19'$. Martensite phase $\mathrm B19$ inside the intermediate layer leads to decrease in the value of lattice microdeformation in the neighbouring phase $\mathrm B2$, which is proportional to the volume share of martensite phase in the layer. Thickness of the layer in which relaxation processes take place according to deformation martensite transformation pattern $\mathrm B2\to\mathrm B19'$ is 10 to 15 mcm.