%0 Journal Article
%T Evolution of Structural-Phase States in TiNi Surface Layers Synthesized by Electron Beam Treatment
%A L. L. Meisner
%A A. I. Lotkov
%A Yu. P. Mironov
%A A. A. Neyman
%J Journal of Nanotechnology
%D 2010
%I Hindawi Publishing Corporation
%R 10.1155/2010/605362
%X The paper presents the results of X-ray diffraction analysis of nonequilibrium structural and elastic stress states in TiNi surface layers irradiated by low-energy electron beams. It is found that a surface layer with a mixed (2D columnar and 3D equiaxial) submicrocrystalline structure is formed on the irradiated side of the TiNi specimens, and the volume fractions of the two structure types depend on the beam energy parameters and number of pulses. The B2 phase synthesized in the layer is characterized by lattice microstrain due to stresses of the first and second kinds ( , ), and the layer as such is an internal stress concentrator for underlying layers of the material. In the intermediate layer beneath the stress concentrator, relaxation of irradiation-induced internal stress takes place. It is shown that the main mechanism of the relaxation is partial martensite transformation. The martensite phase in the intermediate layer decreases the microstrain in the conjugate B2 phase. The thickness of the layer in which the relaxation processes develop through the martensite transformation is 10每15 m. 1. Introduction Recently, there has been intensive development in surface modification of metals by a high current electron beams of moderate and low energy [1每8]. The treatment makes it possible to form surface layers with new physical properties while unaffecting the original features in the material bulk. Crystalline and amorphous states in the layers, as a rule, are metastable since the temperature, pressure, heating and cooling conditions under which they are formed are highly nonequilibrium [7每13]. Available experimental data show that it is these nonequilibrium states in surface layers that ensure new atypical properties attractive for practical applications [14每19]. It is apparent that the new properties are primarily due to the changes in structural-phase states of material and hence in properties of its surface layers on electron beam treatment. However, the information on the thus synthesized structural-phase states and their relation to the change in surface properties of materials is very scanty, and the mechanisms of their formation are poorly known. Electron beam treatment of material gives rise to strong internal stress fields localized in its near-surface volumes [7, 10, 20每23]. In the regions of stress field localization, the material undergoes a change in mechanical properties (an increase in hardness, brittleness, rigidity) [18, 24]; however, there is also evidence that the stress fields adversely affect the chemical properties of the
%U http://www.hindawi.com/journals/jnt/2010/605362/