湿磨时间对超细WC粉末晶体学参数的影响

Effect of Wet-milling Time on Crystallographic Parameters of Ultrafine WC Powder

超过60 h的长时滚动湿磨是目前国内制备超细晶硬质合金最常用的工艺.本文探讨湿磨时间对超细WC粉末晶体学参数的影响规律,旨在论证上述湿磨工艺的合理性.采用滚动湿磨工艺制备WC-0.47Cr3C2-0.28VC-7Co超细混合料,采用Williamson-Hall法和Rietveld拟合法对X射线衍射图谱进行分析.结果表明,与WC原料相比,湿磨50 h和68 h后,WC晶粒尺寸由原始态54 nm分别减小至45 nm和40 nm,降低幅度分别为17%和26%;微观应变由原始态0.16%分别增加至0.17%和0.18%,增加幅度分别为6%和13%,增加幅度不明显;晶格常数a由原始态0.290 43 nm同步减小至0.290 40 nm,晶格常数c由原始态0.283 96 nm分别增加至0.283 97 nm和0.284 01 nm,增减幅度非常小.WC晶体微观应变的小幅变化不会对烧结过程中WC晶粒生长驱动力产生明显影响,适当延长湿磨时间以改善Co在超细WC-Co基混合料中分散均匀性的工艺具有合理性.

Wet-milling in an organic medium for more than 60 h is a common practice in the production of ultrafinegrained cemented carbides.In order to understand the rationality of this wet-milling technique,effect of wet-milling time on the crystallographic parameters of ultrafine WC powder was investigated.Ready-to press powders of WC-0.47Cr3C2-0.28VC-7Co were prepared by wet-milling for different time,i.e.,50 h and 68 h.X-ray diffraction patterns were analyzed by Williamson-Hall and Rietveld refinement methods.The results show that compared with the corresponding parameters of the as-received WC raw material,after wet-milling for 50 h and 68 h,the grain size of WC decreases from 54 nm in the original state to 45 nm and 40 nm,with a reduction rate of 17%and 26%,respectively.The microscopic strain increases from 0.16%of the original state to 0.17%and 0.18%,with a slight increase of 6%and 13%,respectively.The lattice constant a decreases synchronously from 0.290 43 nm in the original powder state to 0.290 40 nm.The lattice constant c increases from 0.283 96 nm in the original state to 0.283 97 nm and 0.284 01 nm,respectively,with a quite small increase or decrease amplitude.A small change in the microscopic strain of WC crystal will not have a significant impact on the growth driving force of WC grain during the sintering process,and it is reasonable to extend the wet grinding time appropriately to improve the dispersion uniformity of Co in ultra-fine WC-Co-based mixture.