Structural changes of the B2 phase in the surface layer of titanium nickelide after pulsed electron-beam treatment

The structural and phase state of titanium-nickelide surface layers after low-energy, high-current electron-beam application is studied by X-ray structural analysis and by optical microscopy and also scanning and transmission electron microscopy. In electron-beam treatment, a nonequilibrium single-phase state is formed in the recrystallized layer (thickness 8–10 μm). This state is characterized by a distorted structure based on B2 phase, textured close to the 〈410〉 direction. The layer at a depth of 10–20 μm contains not only B2 phase with slight lattice distortion but also a small proportion (up to 5 vol %) of phase with martensite B19′ structure. As a result of electron-beam treatment, the chemical composition of the modified layer is changed, with enrichment by titanium on account of the melting of Ti2Ni particles. The range of martensitic transformation is shifted to higher temperatures. Thus, even at room temperature, we may expect that the basic structural state in this layer will be martensite. Transmission electron microscopy indicates that no martensite phase is seen in the modified layer. A hypothesis explaining the structural and phase state at the titanium-nickelide surface after electron-beam treatment is outlined.