Известия Томского политехнического университета: Инжиниринг георесурсов (May 2019)
X-ray diffraction study of structural phase states in TiNi near-surface layers irradiated with pulsed electron beams
Abstract
The relevance of the research is caused by the increasing interest to application of electron-beam treatment as a means of precise changes of structural and phase states, and the properties of the surface and the surface layers of metallic materials. The aim of the work is to study the changes of structura-phase states in the TiNi surface layers depending on the parameters of electron-beam treatment. The methods used in the study: XRD analysis was carried out on a DRON-7 and Shimadzu XRD-6000 diffractometers. The phase composition and the structure of surface and deeper layers were analyzed using X-ray diffraction in symmetric Bragg diffraction geometry (θ-2θmode) and grazing incidence X-ray diffraction in asymmetric Bragg diffraction geometry with a varying incidence angle α, which is the angle between the specimen surface plane and the direction of a primary incident X-ray beam. The microstructure of the TiNi surface layers were examined by transmission electron microscopy on a microscope JEM 2100. The results: It was found that in a TiNi specimen irradiated by a low-energy high-current electron beam with energy densities Е1=15, Е2=20 and Е3=30 J/cm2 , except the reflections from B2 phase on the diffraction patterns, one can observe the reflections corresponding to the martensitic phase B19' and no reflections from the phase Ti2Ni which were observed on the diffraction patterns of the initial samples. It is shown that the B2 phase formed in the modified layer was enriched by titanium, as compared to its initial concentration in that phase before treatment. It has been established that in a TiNi specimen irradiated by a low-energy high-current electron beam with energy densities Е1=15 and Е2=20 J/cm2 there is no martensitic phase B19' in the modified surface layer. In the TiNi specimen irradiated by a low-energy high-current electron beam with energy densities Е3=30 J/cm2 the coating thickness containing martensitic phase increases considerably.
