Gradient changes in structural condition of the B2 phase of NiTi surface layers after electron-beam treatments

Abstract

Structural conditions of the B2 phase of the Ti[49.5]Ni50.5] alloy surface layers before and after electron-beam treatments (pulse duration [tau]=150 [mu]s, number of pulses n=5, beam energy density E<=20 J/cm{2}) were studied by X-ray diffraction analysis. Analysis of the X-ray patternsdemonstrates that surface layers modified by electron beam treatment contain phase with B2{surf} structure. It is revealed that the lattice parameter of the B2{surf} phase in the surface (modified) layer is also higher than the lattice parameter of the B2 phase in the underlying layer ( a[B2]=3.0159+=0.0005 ). The values of lattice parameter of phase B2{surf} amounted a{surf}[B2]=3.0316+=0.0005 Å and a{surf}[B2]=3.0252+=0.0005 Å, for the specimens after electron-beam treatment at E[1]=15 J/cm{2} and E[2] =20 J/cm{2}, respectively. Inflated lattice parameters a{surf}[B2] are associated with changes in the chemical composition and the presence of residual stresses in the surface region of the samples after electron-beam treatments.