Phase composition in NiTi near-surface layers after electron beam treatment and its variation depending on beam energy density

In the work, we study the mechanisms of structural phase state formation in NiTi surface layers after lowenergy pulsed electron beam irradiation depending on the electron beam energy density. It is revealed that after electron beam treatment of the NiTi specimens at energy densities E₁ = 15 J/cm², E₂ = 20 J/cm², and E₃ = 30 J/cm², a series of effects is observed: The absence of the Ti2Ni phase and the presence of new peaks correspond to the B19′ martensite phase with monoclinic structure. Estimation of the relative volume content of the B2 and B19′ phases from the total intensity of their peaks shows that the percentage of the martensite phase increases from ∼5 vol.% in the NiTi specimen irradiated at E₁ = 15 J/cm² to ∼80 vol.% in the NiTi specimen irradiated at E₃ = 30 J/cm². It is found that in the NiTi specimens irradiated at E ≤ 20 J/cm², the layer that contains a martensite phase resides not on the surface but at some depth from it.