采用粉末冶金工艺制备了无晶粒生长抑制剂和添加晶粒生长抑制剂VC的WC-6.5％Co超细硬质合金.利用JSM5600LV扫描电镜观察不同烧结温度条件下制备试样的WC晶粒三维形貌.结果表明:在烧结温度为1 360℃到1 500℃范围内,无晶粒生长抑制剂的合金中,WC晶粒的形貌会从多面体演变为截角的三棱柱;添加晶粒生长抑制剂的合金中,WC晶粒的形貌会由层状结构转变为尖角三棱柱结构.晶粒生长抑制剂的添加,不仅减缓了W/C的溶解-析出过程,而且改变了W/C原子的析出方式.WC晶粒的各个晶面生长速率不同,引起了其晶体三维形貌的变化.对于添加抑制剂的合金来说,在较低温下烧结并延长保温时间不能使晶粒形貌发育充分,只有提高烧结温度,WC晶粒才能发育成完整的尖角三棱柱.
The WC-6.5％Co ultrafine VC-doped and VC-free cemented carbide was prepared by powder metallurgy process,respectively.The three-dimensional morphologies of the WC grains sintered at different sintering temperature were investigated by JSM5600LV scanning electron microscopy.The results show that the morphologies of the WC grains in the VC-free cemented carbide transform from polyhedral structure to truncated triangular prism in the sintering temperature range of 1 360 ℃ to 1 500 ℃;the morphologies of the WC grains in the VC-doped cemented carbide change from layered structure to triangular prism structure with sharp corners.It is shown that the addition of the grain growth inhibitor not only slows down the dissolution and precipitation of W/C,but also changes the precipitation modes of W/C atoms.The growth of different lattice planes of WC crystal is different,which causes the changes of the three-dimensional morphologies of WC grains.For the VC-doped cemented carbide,sintering at low temperature and prolonging holding time cannot make WC grains fully develop;only the increase of the sintering temperature can make WC grains completely grow into triangular prism with sharp corners.
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