MICROSTRUCTURE EVOLUTION IN THE MODIFIED SUBSURFACE LAYER OF TiNi ALLOY UNDER LOW ENERGY HIGH CURRENT PULSED ELECTRON BEAM

The paper is devoted to the effect of pulsed electron-beam treatments with different energy densities Е1 = 15 J/cm2, Е2 = 20  J/cm2 и Е3  =  30 J/cm2 on the change of structural and phase states in the NiTi surface layers. It is revealed that in the diffraction patterns of NiTi specimens with one side irradiated by a low-energy high-current electron beam the refl  ections B2 phase and martensite phase B19′ are observed. By increasing the energy density from Е1 = 15 J/cm2 to Е3  =  30  J/cm2 the content of martensite phase B19′ increases from 5  % to 80 %. It is also revealed that the surface layer is melted to the thickness 8–10  μm, and in this layer the Ti2Ni phase dissolves. The dis-solution of Ti2Ni phase leads to a change in the concentration of Ti and Ni. It is established that the modifi  ed B2 phase in the melted layer is enriched with titanium as compared with its original content in the B2 phase up to irradiation. It is revealed that B19′ phase formation occurs when the surface layers of the samples TiNi are treated with pulsed electron beams with lower values of the energy density in the beam (Е1  =  15  J/cm2,  Е2 = 20 J/cm2). In the samples treated with pulsed elect ron beams with greater energy density in the beam Е3  =  30  J/cm2, the surface layer to the entire depth of penetration of X-ray beam is in the martensitic state. 

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