Materials Science Forum Vols. 561-565

Abstract: The deformation ability of metals and the mechanic characteristics of metal parts are closely related to the material’s microstructure and grain size, so it’s important to study the simulation techniques of microstructure evolution. Common microstructure simulation techniques include digital simulation and graphic simulation. This paper firstly introduced the simulation techniques of microstructure, and then focused on the graphic simulation technique that can directly show grain boundary network’s evolution process. It then built a Monte Carlo model of the grain growth during super plastic deformation, and implemented the graphic illustration of grain growth using Visual Studio software. The result matched well with the experimental outcome, which proved the usability of the technique

Abstract: In this paper, a simplified cellular automaton (CA) model was proposed for modeling the evolution of microstructure in solidification process of AZ91D magnesium alloy. Since the calculation time was significantly reduced, it might be used to predict the microstructure field of a real Mg component after solidification. The stochastic nucleation, competitive growth processes of many grains with various crystallographic orientations and the formation of eutectic structure were also taken into account. Furthermore, step castings were poured with sand and permanent molds and metallographic experiments were carried out for validating the developed models. It was shown that the simulation results are in good agreement with those obtained in the experiments.

Abstract: Slow shot velocity and its acceleration phase in the shot sleeve have great influence on the flow pattern of the liquid metal in the shot sleeve. In this paper, a three-dimensional model based on the SOLA-VOF algorithm was developed and used to simulate the flow of melt in the shot sleeve. The mathematical model was verified by water analog experiments with constant plunger velocities. Based on numerical simulation results, the influences of the plunger acceleration on the wave profile of the liquid metal in the shot sleeve under different fill ratios and sleeve diameters were investigated. The results indicated that in order to avoid air entrapment in the shot sleeve, the optimal acceleration value to the critical slow shot velocity increases with the increase of the fill ratio, and the range of suitable acceleration becomes wider as well. With the same fill ratio, the value of suitable acceleration rises as the plunger diameter increases.

Abstract: The micro structural evolution and the mechanism of recrystallization grain growth were studied during re-aging process in Cu-Ni-Si alloy containing finely pre-aging δ-Ni2Si precipitates using computer simulations based on a diffuse-interface phase-field kinetic model. In this model, the temporal evolution of the spatially dependent field variables is determined by numerically solving the time-dependent Ginzburg-Landau (TDGL) equations for the structural variables. The simulation results quantify the effects of the precipitation on recrystallization. It is shown that the finely dispersed pre-aging δ-Ni2Si precipitates exert a strong pinning effect on the recrystallization grain boundaries. The recrystallization grain growth for r = 3 fa = 0.015 can be described as R =1.04∗t 0.33 at the beginning, followed by a gradual transition to growth stagnation. The final grain size follows a Zener type relation lim 0.49 1.41 a R r f =     for 0.01 ≤ fa ≤ 0.21 and r = 2.5 or 3.

Abstract: In this paper we present an anisotropic compaction model based on a generic modeling framework. The model is a generalization of Hill’s anisotropic model to compressible materials and reduces to a Cam-clay type model in the isotropic limit. The model has been calibrated using experimental data for a commercial steel powder obtained from a computer controlled triaxial cell in which the yield surface was probed following loading along different paths in stress and strain space. Closed-form analytical expressions are presented for the yield surface as a function of the inelastic strain. The model has been implemented in the general purpose finite element code ABAQUS. Simulations are presented which explore the effect of a detailed structure of the constitutive law on the compaction response.

Abstract: Material behaviors of anisotropy and rate sensitivity affect cold ring rolling greatly. So, a self-developed incremental model of rate dependent crystal plasticity (RDCP) is utilized to forecast the deformation characteristics of this forming process based on a 3D FE model under ABAQUS/Explicit environment. The results show that the model of RDCP captures material behaviors of anisotropy and rate sensitivity better in this forming process by the comparison with the model of J2 plasticity; with the decrease of rate sensitivity coefficient, the forming process becomes more unstable with smaller rolling force and growth in ring radial direction; with the increase of feed rate of idle roll, the deformation of ring becomes more even while the rolling force becomes larger.

Abstract: It is commonly considered that the character of atomizing gas-flowing field would affect breaking method of molten metal, liquid droplet size and mass distribution. It is one of the important factors which determine the microstructure and metallurgical quality of products. In this paper, three types of atomizers were designed and Pitot tube was used to investigate the steady state gas flow field generated by a close-coupled spray deposition atomizer. Through the study of atomization gas velocity distribution by simulation and experiment, the construction and gas flow dynamical property were introduced in this paper.

Abstract: A new expression for the chemical bond in perovskite-type oxides is proposed based on the atomization energy concept. The atomization energies,
Eo for oxygen atom and
EM for metal atom in each oxide are evaluated theoretically using the energy density analysis of the total energy, and the 9EO vs. 9EM diagram called atomization energy diagram, is constructed. Every oxide can be located on the atomization energy diagram, although there are significant differences in the nature of the chemical bond among the oxides.

Abstract: Two dimensional simulations of discrete dislocation dynamics were carried out to clarify a shielding effect due to dislocations at a crack tip. The configuration of dislocations around the crack tip was calculated under the conditions of mode I tensile load at high temperatures. The stress field around the crack tip due to dislocations was found to be compressive, accommodating mode I stress intensity at the crack tip. In order to experimentally confirm the stress accommodation, infrared photoelastic observation was also performed in a specimen pre-deformed at high temperatures. The experimental result is in good agreement with a simulated infrared photoelastic image derived from the stress field calculated.