Computer Simulation of the Interphase Boundary Evolution in Ni_(75)Al_xV_(25-x) Alloy

The interphase boundary evolution of ordered phase in Ni75AlxV25-x alloy during precipitation was simulated on atomic-scale based on the microscopic phase-field dynamic model. The results show that the second phase precipitated from the interphase boundary formed by the first phase and the disordered matrix at high temperature, and from the interphase boundaries of the first phase at low temperature. L12 phase had obvious selective orientation when precipitated from the interphase boundaries of D022- L12 phase nucleated easily at the interphase boundaries formed by [10] and [01] directions of D022 projection along [001] direction, and grew easily at [10] direction. There was no the selective orientation when L12 phase precipitated from the interphase boundary formed by D022 and the disordered matrix. D022 phase had the selective orientation when precipitated from the interphase boundaries of L12, and grew along the [10] direction.

THE INVESTIGATION OF KINETICS OF HIGH-TEMPERATURE STRUCTURE TRANSFORMATION OF HOMOPHASES AND HETEROPHASES MATERIALS

The kinetics of internal boundaries relaxation: antiphase domain boundaries and interphase boundaries-in the conditions of high-temperature annealing and the structure transformations are investigated in homophase and heterophase systems. Homophase systems look like ordered binary alloy and include antiphase domain boundaries of various orientation. Clear components border on ordered alloy in heterophase systems and two processes take place simultaneously here-disordering of binary alloy and solution in ordered phase of clear component. Computer experiment is realized in the sphere of temperatures close to the temperature of order-disorder phase transition in the limits of two-dimensional model of atom diffusion at the vacant knots of crystal lattics.

Dislocation-mediated migration of interphase boundaries

Faceted interphase boundaries(IPBs)are commonly observed in lath-shaped precipitates in alloys consisting of simple face-centred cubic(fcc),body centred-cubic(bcc)or hexagonal closed packed(hcp)phases,which normally contain one or two sets of parallel dislocations.The influence of these dislocations on interface migration and possible accompanying long-range strain field remain unclear.To elucidate this,we carried out atomistic simulations to investigate the dislocation-mediated migration processes of IPBs in a pure-iron system.Our results show that the migration of these IPBs is accompanied with the slip of interfacial dislocations,even in high-index slip planes,with two migration modes were observed:the first mode is the uniform migration mode that occurs only when all of the dislocations slip in a common slip plane.A shear-coupled interface migration was observed for this mode.The other interfaces propagate in the stick-slip migration mode that occurs when the dislocations glide on different slip planes,involving dislocation reaction or tangling.A quantitative relationship was established to link the atomic displacements with the dislocation structure,slip plane,and interface normal.The macroscopic shear deformation due to the effect of overall atomic displacement shows a good agreement with the results obtained based on the phenomenological theory of martensite crystallography.Our findings have general implications for the understanding of phase transformations and the surface relief effect at the atomic scale.

Influence of Features of Interphase Boundaries on Mechanical Properties and Fracture Pattern in Metal-Ceramic Composites

The results of a theoretical study on the influence of strength of interphase boundaries in metal-ceramic composite on macroscopical characteristics of composite response such as strength, deformation capacity, fracture energy and fracture pattern are presented. The study was conducted by means of computer-aided simulation by means of movable cellular automaton method taking account of a developed ＂mesoscopical＂ structural model of particle-reinforced composite. The strength of interphase boundaries is found to be a key structural factor determining not only the strength properties of metal-ceramic composite, but also the pattern and rate of fracture. The principles for achievement of the high-strength values of particle/binder interfaces in the metal-ceramic composition due to the formation of the wide transition zones （areas of variable chemical composition） at the interphase boundaries are discussed. Simulation results confirm that such transition zones provide a change in fracture mechanism and make the achievement of a high-strength and a high deformation capacity of metal-ceramic composite possible.

Migration of δ/γ Interface in Low Carbon Steels during Continuous Cooling

The δ-ferrite to γ-austenite phase transformation process of low carbon steel was observed in-situ under a confocal scanning laser microscope and the influence of manganese and chromium on the migration of δ/γ interphase boundary during theδ to γphase transformation was studied. It was found that the δ/γ interphase boundary becomes unstable with the decrease of temperature, from planar to curved morphology during theδ to γ phase transformation of Fe-0.08C steel and Fe-0.08C-0.8Mn steel. But in Fe-0.08C-0.8Cr steel, the δ/γ interphase boundaries are stable with planar morphology during the whole δ-ferrite to γ-austenite transformation. The destabilization of δ/γ inter- phase boundary in Fe-0.08C and Fe-0.08C-0.8Mn steels results from high degree of supercooling and sub-boundaries in 7, respectively. The stabilization of δ/γ interphase boundary in Fe-0.08C-0.8Cr steel results from the slow diffu- sion rate of carbon atom induced by the addition of chromium.

Effect of Surface Layer Structural-Phase Modification on Tribological and Strength Properties of a TiC–(Ni–Cr) Metal Ceramic Alloy

This paper reports TiC–（Ni–Cr） metal ceramic alloy（ratio of components 50：50） with nanoscaled components formed in the surface layer and smoothly transformed into the initial inner structure throughout the material under pulsed electron irradiation of the alloy surface. Principal changes in the surface layer are ascribed to the formation of gradient structure leading to the increase in wear resistance of the surface layer, drop of friction coefficient and improvement of specimen bending resistance when stressing on the irradiated surface side. The above changes of tribological and strength properties in the surface layer under pulsed electron irradiation become more apparent with increasing atomic mass of a plasma-forming inert gas.