纳米晶W-Ni-Fe复合粉末烧结过程中的致密化与显微组织演变

Densification and microstructure evolution of nanocrystalline W-Ni-Fe composite powders during sintering

采用溶胶喷雾干燥-热还原法制备纳米晶93W-4.9Ni-2.1Fe复合粉末,利用高温热膨胀仪测定和研究纳米晶复合粉末的烧结收缩动力学曲线特征,计算纳米晶W-Ni-Fe复合粉末的固相烧结激活能,并利用金相显微镜和扫描电镜分析致密化过程中显微组织的演变规律。研究结果表明:纳米晶W-Ni-Fe复合粉末的开始收缩和剧烈收缩温度分别为900℃和1 120℃,其最大的线收缩率达0.097%/℃;在1 200℃以下的固相烧结阶段,压坯便发生显著的致密化,其致密化程度可达98%以上,固相烧结的表观激活能为154.83 kJ/mol,比传统粉末烧结激活能大大降低;在固相烧结期间,W晶粒尺寸长大缓慢,在1 380℃以上液相烧结时W晶粒长大急剧加快。

Nanocrystalline 93W-4.9Ni-2.1Fe composite powders were synthesized by sol-spray drying and subsequent hydrogen reduction process.The characteristics of swell-shrinkage kinetic curve were investigated by high temperature dilatometer.The apparent activation energy during solid phase sintering was calculated.Additional,optical microscope and scanning electron microscope（SEM） were employed to characterize the microstructure evolution of the alloys during densification.The results show that commence shrinkage temperature and sharp shrinkage temperature of the nanocrystalline powders are 900 ℃ and 1 120 ℃ respectively.The maximum shrinkage rate is 0.097 %/℃.The densification of the nanocrystalline powders mainly occurs during the solid phase state sintering.The apparent activation energy during the solid-phase sintering stage is approximately 154.83 kJ/mol,which is much lower than that of the conventional mixed powders.The grain grows slowly during the solid phase state sintering.When the sintering temperature is above 1 380 ℃,the liquid phase sintering starts simultaneously with the rapid growth of the tungsten grains.