Vacuum thermal diffusion technique was applied to preparing alloying coating on AZ31 B magnesium alloy. The microstructure and phase composition of the coatings prepared at different holding time were investigated in ...Vacuum thermal diffusion technique was applied to preparing alloying coating on AZ31 B magnesium alloy. The microstructure and phase composition of the coatings prepared at different holding time were investigated in detail using optical microscopy（OM）, scanning electron microscopy（SEM）, energy dispersive spectrometer（EDS） and X-ray diffraction（XRD）, and so on. The microhardness tester and electrochemical workstation（PS-168a） were used to measure the microhardness and corrosion resistance of the alloying coating. The results showed that the alloying coatings gradually generated with the extension of holding time under constant temperature. And the obvious bonding interface between the coating and substrate was observed, and the bonding interface was changed from smooth to zigzag. EDS and XRD analyses showed that the microstructure of alloying coating mainly consisted of eutectic α-Mg phase and continuous network β-Al（12）Mg（17） phase. The average microhardness of the coatings increased by 113% in comparison to the substrate, and the self-corrosion potential increased from-1.389 to-1.268 V at the same time.展开更多
An attempt was made to optimize friction welding parameters to attain a minimum hardness at the interface and a maximum tensile strength of the dissimilar joints of AISI 304 austenitic stainless steel （ASS） and copp...An attempt was made to optimize friction welding parameters to attain a minimum hardness at the interface and a maximum tensile strength of the dissimilar joints of AISI 304 austenitic stainless steel （ASS） and copper （Cu） alloy using response surface methodology （RSM）. Three-factor, five-level central composite design matrix was used to specify experimental conditions. Twenty joints were fabricated using ASS and Cu alloy. Tensile strength and interface hardness were measured experimentally. Analysis of variance （ANOVA） method was used to find out significant main and interaction parameters and empirical relationships were developed using regression analysis. The friction welding parameters were optimized by constructing response graphs and contour plots using design expert software. The developed empirical relationships can be effectively used to predict tensile strength and interface hardness of friction welded ASS-Cu joints at 95% confidence level. The developed contour plots can be used to attain required level of optimum conditions to join ASS-Cu alloy by friction welding process.展开更多
The steel bonded carbide, a composite material, is very difficult to be machined to a fine finish mirror surface. In this paper, an electrolytic in-process dressing (ELID) grinding with metallic bond super-hard abrasi...The steel bonded carbide, a composite material, is very difficult to be machined to a fine finish mirror surface. In this paper, an electrolytic in-process dressing (ELID) grinding with metallic bond super-hard abrasive wheel was developed for grinding steel bonded carbide GT35. Factors affecting ELID grinding performance were analyzed by an atomic force microscope (AFM). Based on the analysis of AFM topography of the fine ground mirror surface of the steel bonded carbide, a schematic diagram of the mechanism of micro-removal of the ground surface was described. The AFM topography also shows that the hard brittle carbide particles, on the surface of steel bonded carbide, were machined out by ductile cutting. Since the grinding cracks in the ground surface are due to temperature gradient, temperature distribution in the grinding area was analyzed by finite element method (FEM). Experimental results indicate that a good mirror surface with Ra<0.02pm can be obtained by the developed ELID grinding system.展开更多
To improve the surface properties,lining of magnesium alloys with hard powders by shot peening was carried out in order. The hard powders were tried to bond to the workpiece surface due to the collision of many shots....To improve the surface properties,lining of magnesium alloys with hard powders by shot peening was carried out in order. The hard powders were tried to bond to the workpiece surface due to the collision of many shots.In order to fix the hard powders to the surface of the workpiece,the powders were set on an uneven surface.To easily facilitate fixing of powders,lining of the workpiece with the powder sandwiched between two aluminum foil sheets was also attempted.In this experiment,a centrifugal shot peening machine with an electrical heater was employed.The workpieces were magnesium alloys AZ31B and AZ91D,and the hard powders were commercial cemented carbide,alumina,and zirconia.The joinability of hard powders near the lined surface was observed by a optical microscope.The wear resistance was also evaluated by a wear test.The hard powders were successfully bonded to the surface of workpieces by the shot lining process.The results show that the present method is effective in wear resistance of the magnesium alloys.展开更多
The development of a high-performance cemented carbide drill bit is of great significance to the reduction of rock drilling-cost. The non-smooth features of a biological surface provide an insight into how they can ob...The development of a high-performance cemented carbide drill bit is of great significance to the reduction of rock drilling-cost. The non-smooth features of a biological surface provide an insight into how they can obtain low friction and good wear resistance with evolving surface morphology. By analyzing the mechanism of the surface of a dung beetle for reducing soil wear and adherence, we design a cemented carbide drill bit with a bionic surface, which is expected to have superior anti-wearing and anti-sticking properties for drilling the soft coal seam. Inspired from the characteristics of the head and pronotum surface of the dung beetle, optimized non-smooth surface of the drill bit was constructed. The working performance of this innovative drill was experimentally tested. With comparative experiments under the identical drilling conditions, the wear rates, drilling times of conventional drills and bionic drills were measured. Compared with the conventional counterpart, the drill designed exhibits better performance in reducing wear and sticking drilling-breaks, therefore achieving higher levels of efficiency. The diameter of the dome and pit on the bit surface is in the range of 0.8–1.2 mm, and the bionic drill bits could get better performance with preferable drilling speeds and wear rates.展开更多
基金Project(2015GY167)supported by the Science and Technology Department of Shaanxi Province,ChinaProject(2014cxy-05-1)supported by the Science and Technology Bureau of Yulin,China
文摘Vacuum thermal diffusion technique was applied to preparing alloying coating on AZ31 B magnesium alloy. The microstructure and phase composition of the coatings prepared at different holding time were investigated in detail using optical microscopy（OM）, scanning electron microscopy（SEM）, energy dispersive spectrometer（EDS） and X-ray diffraction（XRD）, and so on. The microhardness tester and electrochemical workstation（PS-168a） were used to measure the microhardness and corrosion resistance of the alloying coating. The results showed that the alloying coatings gradually generated with the extension of holding time under constant temperature. And the obvious bonding interface between the coating and substrate was observed, and the bonding interface was changed from smooth to zigzag. EDS and XRD analyses showed that the microstructure of alloying coating mainly consisted of eutectic α-Mg phase and continuous network β-Al（12）Mg（17） phase. The average microhardness of the coatings increased by 113% in comparison to the substrate, and the self-corrosion potential increased from-1.389 to-1.268 V at the same time.
文摘An attempt was made to optimize friction welding parameters to attain a minimum hardness at the interface and a maximum tensile strength of the dissimilar joints of AISI 304 austenitic stainless steel （ASS） and copper （Cu） alloy using response surface methodology （RSM）. Three-factor, five-level central composite design matrix was used to specify experimental conditions. Twenty joints were fabricated using ASS and Cu alloy. Tensile strength and interface hardness were measured experimentally. Analysis of variance （ANOVA） method was used to find out significant main and interaction parameters and empirical relationships were developed using regression analysis. The friction welding parameters were optimized by constructing response graphs and contour plots using design expert software. The developed empirical relationships can be effectively used to predict tensile strength and interface hardness of friction welded ASS-Cu joints at 95% confidence level. The developed contour plots can be used to attain required level of optimum conditions to join ASS-Cu alloy by friction welding process.
文摘The steel bonded carbide, a composite material, is very difficult to be machined to a fine finish mirror surface. In this paper, an electrolytic in-process dressing (ELID) grinding with metallic bond super-hard abrasive wheel was developed for grinding steel bonded carbide GT35. Factors affecting ELID grinding performance were analyzed by an atomic force microscope (AFM). Based on the analysis of AFM topography of the fine ground mirror surface of the steel bonded carbide, a schematic diagram of the mechanism of micro-removal of the ground surface was described. The AFM topography also shows that the hard brittle carbide particles, on the surface of steel bonded carbide, were machined out by ductile cutting. Since the grinding cracks in the ground surface are due to temperature gradient, temperature distribution in the grinding area was analyzed by finite element method (FEM). Experimental results indicate that a good mirror surface with Ra<0.02pm can be obtained by the developed ELID grinding system.
文摘To improve the surface properties,lining of magnesium alloys with hard powders by shot peening was carried out in order. The hard powders were tried to bond to the workpiece surface due to the collision of many shots.In order to fix the hard powders to the surface of the workpiece,the powders were set on an uneven surface.To easily facilitate fixing of powders,lining of the workpiece with the powder sandwiched between two aluminum foil sheets was also attempted.In this experiment,a centrifugal shot peening machine with an electrical heater was employed.The workpieces were magnesium alloys AZ31B and AZ91D,and the hard powders were commercial cemented carbide,alumina,and zirconia.The joinability of hard powders near the lined surface was observed by a optical microscope.The wear resistance was also evaluated by a wear test.The hard powders were successfully bonded to the surface of workpieces by the shot lining process.The results show that the present method is effective in wear resistance of the magnesium alloys.
基金supported by the National Natural Science Foundation of China(Grant Nos.51204122&51134018)the Natural Science Foundation of Jiangsu Province(Grant No.BK20140411)+3 种基金State Key Laboratory of Mechanics and Control of Mechanical Structures(Nanjing University of Aeronautics and AstronauticsMCMS-0414Y01)the National Basic Research Program of China(“973”Project)(Grant No.2014CB239203)the 111 Project(Grant No.B14006)
文摘The development of a high-performance cemented carbide drill bit is of great significance to the reduction of rock drilling-cost. The non-smooth features of a biological surface provide an insight into how they can obtain low friction and good wear resistance with evolving surface morphology. By analyzing the mechanism of the surface of a dung beetle for reducing soil wear and adherence, we design a cemented carbide drill bit with a bionic surface, which is expected to have superior anti-wearing and anti-sticking properties for drilling the soft coal seam. Inspired from the characteristics of the head and pronotum surface of the dung beetle, optimized non-smooth surface of the drill bit was constructed. The working performance of this innovative drill was experimentally tested. With comparative experiments under the identical drilling conditions, the wear rates, drilling times of conventional drills and bionic drills were measured. Compared with the conventional counterpart, the drill designed exhibits better performance in reducing wear and sticking drilling-breaks, therefore achieving higher levels of efficiency. The diameter of the dome and pit on the bit surface is in the range of 0.8–1.2 mm, and the bionic drill bits could get better performance with preferable drilling speeds and wear rates.
