球磨参数对纳米WC晶格畸变和烧结晶粒长大的影响

Effects of Ball Milling Conditions on Lattice Distortion and Early Growth of WC Grains in Cemented Carbides

配置成分为WC-10%Co混合料,采用不同球料比(6:1与18:1)、不同球磨时间(4、8、16、32、48和72 h),以酒精为介质滚动球磨,干燥后压制成尺寸为6.5 mm×5.25mm×20 mm的试样,然后在H_2气氛下在1 340℃烧结,得到硬质合金试样,通过X射线衍射(XRD),扫描电子显微镜(SEM)等分别研究混合料中WC晶粒尺寸、内应变和晶格畸变等与球料比、球磨时间的关系。结果表明:(1)对于纳米级WC粉末,实验中的球磨过程不能破碎其晶粒;(2)随球磨时间延长,WC晶粒的内应变与晶格畸变呈先快后慢的增长方式,球料比越大,增速转折点越早出现;晶格的具体畸变形式与球料比相关;(3)在球料比6:1混合料中WC颗粒内发现"泊松效应";(4)在较低的内应变和WC邻接程度情况下,烧结早期WC晶粒合并长大所需的能量势垒较高,能够有效抑制WC晶粒早期长大。

WC-10%Co powders were ball milled for different time（4, 8, 16, 32, 48 and 72 h） at ball-to-powder ratio（6：1 and 18：1）, respectively. The resulting mixtures were pressed into samples with size of 6.5 mm×5.25 mm×20 mm and then heated under H_2 at 1 340 ℃ to obtained final cemented carbide samples. Grain size, internal strain, lattice distortion,evolution of morphology and oxidation of as-milled powders as a function of time were studied by X-ray diffraction（XRD）,scanning electron microscope（SEM）, specific surface area measurement and oxygen content analyzer, respectively,. It shows that：（1） nano WC powders could not be broken by ball milling here;（2） internal strain and lattice distortion of WC grains increase fast first and then slow down later with milling time; the larger the ball-to-powder ratio, the earlier the turning point of increasing speed appeared; the specific way of lattice distortion was strongly affected by ball-to-powder ratio（3） ＂Poisson effect＂ was found inside WC grains through lattice distortion of as-milled samples at 6：1 ball-to-powder ratio; and（4） under severe mechanical straining, as-milled powders tended to agglomerate and provide high speed diffusion paths during sintering,leading to early growth of WC grains via coalescence.