Papers by Author: Ming Min Huang

Abstract: Numerical simulation of temperature field on friction stir welded 7022 aluminum alloy was studied in this paper. A new dual-source model has been designed and applied to investigate the variation of temperature field over time. Result shows that temperature of the nodes along the welding line increased at first and then decreased, the highest nodal temperature of 524°C presents at the ending position. Temperature of the nodes perpendicular to the welding line rises rapidly when the source arrived and falls rapidly when it left, and then cools to room temperature linearly when the source is removed. Simulative result predicts large temperature difference on the plates, and thermal pretreatment should be conducted before welding.

Abstract: The performance of Atomic Force Microscope (AFM) is greatly determined by the quality of its probe. Nowadays, probes of diamond tips have become more and more popular than silicon ones, and have been widely used in industries. In this paper, research about the fabricating of nanocrystalline diamond (NCD) coated AFM probe has been done using Hot-Filament Chemical Vapour Deposition (HFCVD) technique. The results showed that NCD films have been grown on the probe. Problems about the growth of NCD on the tips have been discussed. The optimum parameters have also been proposed. This research can provide reference for the further experiments on the fabrication of NCD coated tips.

Abstract: In order to provide effective guarantee for the prediction of residual stress and deformation after welding process of large-sized aluminum alloy structures, temperature field and thermal efficiency during double-sided multi-layer TIG welding of aluminum alloy was studied. By integratedly considering temperature-depended material properties, convection, radiation, filling rate of solders, et al, numerical analysis about the form of molten pool and temperature field was given. Element birth and death technique was taken during the simulation. Double-sided multi-layer TIG welding experiment was carried out and sample of cross section of weld seam after welding was prepared. By trying different thermal efficiency for calculation, simulation result consistent with experimental result was obtained finally, making the present thermal efficiency as the aim result for study. Confirmation was given by comparing temperature value from experiment with simulation one.

Abstract: From the laser welding actual process, the welding heat source model of laser welding process was established, that is, superposition heat source. According to the knowledge of thermodynamics, the establishment of a welding process, the mathematical model of temperature distribution of laser welding process was obtained by laser welding heat source. Finally, the finite element simulation of welding temperature distribution was used. The simulated results were compared with the analytical results of mathematical model of temperature field, it was proved consistent between simulated results and analytical results, at the same time it can account for the correctness of the mathematical model of temperature field.

Abstract: NiCoCrAlY coatings strengthened by different content of nano-Al2O3p, using crosscurrent CO2 laser, were prepared on Ni-based superalloy substrates, and thermal shock behaviors of these coatings were investigated by cycling between 1050°C and room temperature (forced water quenching).The results show that the thermal shock resistances of nano-Al2O3p-added coatings are definitely better than that without adding nano-Al2O3p. Among the nano-Al2O3p-added coatings, the coating added with 0.5wt% nano-Al2O3p performs best. After 10 thermal shock cycles, the spalled and spalling area in the oxide scale of the no-nano-Al2O3p coating reaches up to 27.7%, and the main failure form of the oxide scale is an expanding unit-spalling type in thermal shock cycles. While the area in the oxide scale of nano-Al2O3p-added coatings is only 10%~60% to the no-nano-Al2O3p one, and the failure of these oxide scales is mainly in the form of unit-spalling type. After 100 thermal shock cycles, many cracks turn up in the cross-section of the no-nano-Al2O3p coating, including propagating crack and internal crack. While no internal crack appeared in nano-Al2O3p-added coatings, and the propagating cracks are smaller than no-nano-Al2O3p one.