Xianhui Wang

Arc erosion behaviors of AgSnO2 contact materials prepared with different SnO2 particle sizes

To clarify the effect of SnO2 particle size on the arc erosion behavior of AgSnO2 contact material, Ag–4%SnO2 (mass fraction) contact materials with different sizes of SnO2 particles were fabricated by powder metallurgy. The microstructure of Ag–4%SnO2 contact materials was characterized, and the relative density, hardness and electrical conductivity were measured. The arc erosion of Ag–4%SnO2 contact materials was tested, the arc duration and mass loss before and after arc erosion were determined, the surface morphologies and compositions of Ag–4%SnO2 contact materials after arc erosion were characterized, and the arc erosion mechanism of AgSnO2 contact materials was discussed. The results show that fine SnO2 particle is beneficial for the improvement of the relative density and hardness, but decreases the electrical conductivity. With the decrease of SnO2 particle size, Ag–4%SnO2 contact material presents shorter arc duration, less mass loss, larger erosion area and shallower arc erosion pits.

Investigation on preparation, microstructure, and properties of AgTiB2 composite

AgTiB2 composites with different contents of TiB2 were prepared by high-energy milling and powder metallurgy. The morphology and size of the milled Ag/TiB 2 compound powders were characterized by a scanning electron microscopy and a laser particle analyzer. The effect of sintering temperature and TiB 2 content on the microstructure and properties of AgTiB2 composite was studied. The results show that: (1) with increase of the milling time, the powders become finer and more uniform. Nevertheless, the powders begin to coarsen and agglomerate above a certain milling time. In the range of experiments, the desired powders with a relative uniform size can be obtained at 60 h; (2) the increase in TiB2 content results in serious agglomerations of TiB2 in the AgTiB2 composites; and (3) the Ag—0.25 wt%TiB2 composite has a good combination of properties after sintering at 750° C for 2 h, and the hardness and electrical conductivity are 73.3HV and 17.8 MS m-1, respectively.AgTiB2 composites with different contents of TiB2 were prepared by high-energy milling and powder metallurgy. The morphology and size of the milled Ag/TiB 2 compound powders were characterized by a scanning electron microscopy and a laser particle analyzer. The effect of sintering temperature and TiB 2 content on the microstructure and properties of AgTiB2 composite was studied. The results show that: (1) with increase of the milling time, the powders become finer and more uniform. Nevertheless, the powders begin to coarsen and agglomerate above a certain milling time. In the range of experiments, the desired powders with a relative uniform size can be obtained at 60 h; (2) the increase in TiB2 content results in serious agglomerations of TiB2 in the AgTiB2 composites; and (3) the Ag—0.25 wt%TiB2 composite has a good combination of properties after sintering at 750° C for 2 h, and the hardness and electrical conductivity are 73.3HV and 17.8 MS m-1, respectively.

Preparation of Cu/Cr2O3 Composites by Mechanical Activation and In Situ Oxidation

In order to improve the in situ oxidation kinetic condition of Al in Cu matrix, Cr, instead of Al was in situ oxidized to form Cu/Cr2O 3 composites in the present investigation, Cu-Cr powders with different solubilities after mechanical activation were utilized to synthesize Cu/Cr 2O3 composites, and their microstructure and stability were analyzed. The results show that although the Cu-Cr powders suffer from the same mechanical activation; Cr2O3 particles formed by the powders with different solubilities have great differences in size, amount, and distribution. In the range of experiments, the Cu/Cr2O 3 composite formed by Cu-Cr powders with 67% solution has large amounts of finer Cr2O3 particles uniformly distributed in Cu matrix and the best stability at elevated temperatures.In order to improve the in situ oxidation kinetic condition of Al in copper matrix, Cr, instead of Al was in situ oxidized to form Cu/Cr 2 O 3 composites in the present investigation, Cu-Cr powders with different solubilities after mechanical activation were utilized to synthesize Cu/Cr 2 O 3 composites, and their microstructure and stability were analyzed. The results show that although the Cu-Cr powders suffer from the same mechanical activation, Cr 2 O 3 particles formed by the powders with different solubilities have great differences in size, amount, and distribution. In the range of experiments conducted, the Cu/Cr 2 O 3 composite formed by Cu-Cr powders with 67% solution has large amounts of finer Cr 2 O 3 particles uniformly distributed in the copper matrix and exhibited the best stability at elevated temperatures.

Relationship between powder characteristic and internal oxidation of Al in Cu-Al pre-alloyed powders

Since Cu-Al powder characteristics have important effects on the preparation of Cu/Al 2 O 3 composite, the apparent activation energy of Al internal oxidation reaction in Cu-Al pre-alloyed powders with different characteristics was calculated in the present investigation. The microstructure and properties of the synthesized Cu/Al 2 O 3 were studied. The results show that high-energy milling can obviously promote internal oxidation of Al in Cu-Al powders in the same solid solubility. At the same milling conditions and internal oxidation parameters, the solid solution of Al in Cu either in low or high amount will result in the poor microstructure and properties of the Cu/Al 2 O 3 composite. Subsequently, when high-energy milling and internal oxidation are synchronously used to prepare the Cu/Al 2 O 3 composite, there should be an appropriate solubility and milling effect for the pre-alloyed powders.

Simulation of the neck growth of non-isometric biosphere during initial sintering

Because powders are mostly non-isometric during the sintering process, copper powders were chosen to study the effects of four material transport mechanisms, including surface diffusion, grain-boundary diffusion, volume diffusion, and multi-couplings. These material transport mechanisms were studied with respect to sintering neck growth of a non-isometric biosphere during initial sintering. The evolution of the neck growth in the four transport mechanisms was simulated by Visual C++ as well based on the model of different particles. The results show that the increase of the sintering temperature, both the grain-boundary diffusion and volume diffusion play primary roles in neck growth, while surface diffusion gradually becomes the secondary mechanism. Both the sintered neck and the shrinkage of the two centers increase with increasing temperature by means of the coupling diffusion mechanism. The radius of the sintering neck decreased, and the shrinkage rate of the two centers increased with an increase of the diameter ratio of the two spheres.