最新色国产精品精品视频,中文字幕日韩一区二区不卡,亚洲有码转帖,夜夜躁日日躁狠狠久久av,中国凸偷窥xxxx自由视频

Ultrafine/nanocrystalline W-20Cu (mass fraction) composite powders were synthesized by sol-spray drying and subsequent hydrogen reduction process. The powders compacts were sintered at various sintering temperatures for different holding time and then were rapidly quenched in water. The sintering densification and microstructure evolution were investigated. The results show that significant densification occurs at the sintering temperature ranging from 1000 to 1200 oC and 96.4% theoretical density can be realized when sintered at 1200 oC for 60 min. When the sintering temperature is further elevated to 1420 oC and the holding time is 90 min, the relative density of the sintered compacts exceeds the level of 99%. In the range of 1100-1420 oC, the activation energy of sintering densification decreases with the sintering temperature increasing and the value decreases from 276.3 kJ/mol at 1100 oC to 29.1 kJ/mol at 1420 oC. There is no obvious grain growth during the sintering stage below 1200 oC, whereas the grain coarsening is very rapid when the sintering temperature is above 1300 oC. As the sintering temperature increasing, the tungsten grains become spherical. In addition, the grain coarsening at the temperature of 1420 oC is in good agreement with the Ostwald mechanism and the grain coarsening kinetic coefficient is 0.024 μm3/min