X-ray diffraction study of residual elastic stress and microstructure of near-surface layers in nickel-titanium alloy irradiated with low-energy high-current electron beams

In the work, we compare quantitative estimates of residual stresses in nickel-titanium (NiTi) alloy surface layers after electron beam treatment. The quantitative estimates to be compared were taken using X-ray diffraction (XRD) techniques with symmetric and asymmetric Bragg diffraction geometries. A method of quantitative X-ray diffraction estimation of residual stresses in materials with gradient changes in microstructure and physical properties, including elastic moduli, is described. It is found that in a NiTi specimen with one side irradiated by a low-energy high-current electron beam, the maximum residual elastic stresses σ ≈550 MPa are localized in the modified surface layer (melted by the electron beam and rapidly quenched), whereas the residual elastic stresses in the underlying layer with initial B2 structure are no greater than ∼100 MPa. It is for this reason that stress-induced B19′ martensite is formed in the material layer beneath the modified layer.