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

摘要

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= 10 J/cm(2), number of pulses N=10, and pulse duration tau=50 mu s. 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 8-10 mu m thick. This layer is in a single-B2 phase state with distorted structure, lattice parameters a=b = 3.003-3.033 A, c = 3.033-3.063 A and alpha = 89.3-90 degrees, beta= gamma =90 degrees, quasihomogeneous chemical composition corresponding to Ti51.7Ni48.3, the preferred orientations of the crystallites in a direction close to < 4 1 0 >(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. (C) 2014 Elsevier B.V. All rights reserved.