溶胶-凝胶法结合二步烧结制备陶瓷刚玉磨料的微结构控制及晶粒细化机理

Microstructure control and grain refinement mechanism of ceramic corundum abrasives prepared by sol-gel combined with two step sintering process

以6μm粒径的拟薄水铝石为原料,采用溶胶-凝胶法制备含La_(2)O_(3)-TiO_(2)-SiO_(2) 复合添加剂的陶瓷刚玉磨料的前驱体,然后分别采用传统烧结方法和二步烧结法制备陶瓷刚玉磨料。利用扫描电镜和透射电镜分析磨料的微观结构和元素分布,并采用imagePro软件对晶粒尺寸进行分析。结果表明,采用二步烧结法时,第一段烧结的温度显著影响磨料的最终晶粒尺寸。第二段烧结由于温度较低,烧结机制由晶界迁移变为晶界扩散,从而显著细化晶粒,并避免晶粒异常长大。适当降低第二段的烧结温度有利于获得分布均匀的细小等轴晶,但会导致磨料密度降低。与传统烧结法制备的刚玉磨料相比,二步烧结的磨料虽然密度降低,但晶粒细小、尺寸均匀,磨料仍具有较高的硬度。采用第一段和第二段烧结温度分别为1 300℃和1 200℃(保温10 h)的二步烧结法,可获得细小而均一的等轴晶,平均晶粒尺寸为(334±97) nm,密度和硬度(HV)分别为3.87 g/cm^(3)和(18.3±0.29) GPa。

Ceramic corundum abrasive precursor containingLa_(2)O_(3)-TiO_(2)-SiO_(2) composite additive was prepared by sol-gel method using pseudo boehmite with grain diameter of 6μm as raw material.The ceramic corundum abrasives were prepared by conventional sintering method and two-step sintering method,respectively.The microstructure and element distribution of abrasives were analyzed by SEM and TEM,and the grain sizes were analyzed by imagePro software.The results show that the temperature of the first sintering stage significantly affects the final grain size of the abrasive when the two-step sintering method is adopted.Due to the low temperature in the second sintering stage,the later sintering mechanism changes from grain boundary migration to grain boundary diffusion,thus the grains are significantly refined and the abnormal grain grow this avoided.Appropriately reducing the sintering temperature in the second stage is conducive to obtaining fine equiaxed grains with uniform distribution,but it will lead to a decrease in abrasive density.Compared with the corundum abrasives prepared by the traditional sintering method,the abrasives prepared by the two-step sintering method have a smaller grain size,uniform size and high hardness,although the density is reduced.Fine and uniform equiaxed grains are obtained by two-step sintering at 1 300℃and 1 200℃for 10 h,respectively.The average grain size is (334±97) nm,and the density and hardness (HV) are 3.87 g/cm^(3) and (18.3±0.29) GPa,respectively.