Papers by Author: Guo Quan Liu

Abstract: 50vol. %Si/Al composite was prepared by the separation of liquid and solid in semi-solid. The microstructures of composite were obtained using OM, SEM and EMPA. The primary Si particles distribute uniformly on the Al matrix which surrounds the Si particles and makes-up a continuous network. The thermal expansion coefficient and thermal conductivity of composites experienced different thermal process were examined. It shows that the thermal process history has a significant effect on the microstructure and properties. The residual stress and size of Si particles varied during thermal processing which were responsible for the thermal expansion coefficient alternation. The thermal process of high temperature insostatic pressing reduces the porosity in composite and improves thermal conductivity obviously

Abstract: The growth of nano CVD diamond films on low index faces such as (111) face and (100) face under different proposed surface chemical reaction model was simulated by using Kinetic Monte Carlo (KMC) method from atomic scale. The results, for example the influence of deposition time t, substrate temperature T_s, and atomic hydrogen concentration [H] on the film deposition rate, surface roughness, and H embedded in the film under different processing conditions, were systematically analyzed and compared. And the adsorption of various species on {111}-oriented diamond cluster was preliminarily computed from electronic scale by Local Density Approximation (LDA) method to assist understanding the surface adsorption mechanism. It is indicated that the film morphology and quality obtained from atomic scale KMC simulation varies according to the chemical reaction models. And our initial electronic scale computation on {111}-oriented diamond cluster showed that single-carbon species can be adsorbed on the activated site more easily than double-carbon species and the former will result in a more stable state than the latter. In order to reveal the nano CVD diamond film growth mechanism, more work about various species adsorption on many different morphological CVD diamond surfaces is needed.

Abstract: The hot deformation behavior of Nb-V-Ti microalloyed steel in the temperature range of 850°C～1100°C and the strain rate range of 0.001s-1～30s-1 was investigated by establishing the processing maps. The strain rate sensitivity (m), power dissipation efficiency (η) and instability parameter were calculated based on the experimental compression data and are plotted in the temperature–strain rate plane to obtain power dissipation and instability maps. The processing maps exhibit that the deformation at 1000°C and 2s-1 is one peak efficiency of power dissipation of 21%, the deformation at 1050°C and 0.01~0.001 s-1 is another peak efficiency of power dissipation of 45%. The optical microstructure observations show that they represent two dynamic recrystallization domains. Based on the above processing maps, the hot working parameters were optimized.