Cross-sectional TEM analysis of structural phase states in TiNi alloy treated by a low-energy high-current pulsed electron beam

Abstract

The paper reports on a study of structural phase states and their cross-sectional in-depth evolution from the surface of TiNi specimens treated by low-energy high-current electron beams with surface melting at a beam energy density E=10J/cm2, number of pulses N=10, and pulse duration τ=50μs. After treatment, the modified TiNi surface zone takes on a layered structure in which each layer differs in phase composition and structural phase state. It is found that the melted layer is 8–10μm thick. This layer is in a single-B2 phase state with distorted structure, lattice parameters a=b=3.003–3.033Å, c=3.033–3.063Å and α=89.3–90°, β=γ=90°, quasihomogeneous chemical composition corresponding to Ti51.7Ni48.3, the preferred orientations of the crystallites in a direction close to 〈410〉B2, and inhomogeneous lattice strain. The intermediate layer contains, in addition to the B2 phase, a B19′ martensite phase. The structural state of the B2 phase in this layer is close to equilibrium and its parameters approximate those of the initial B2 phase in nonirradiated TiNi specimens.