Microstructure And Property Optimization Of Ceramic Corundum Abrasives

Corundum abrasive with high strength,high toughness,high hardness,good wear resistance,and longer service life has received extensive applications in a variety of fields.In this paper,the corundum abrasive precursors were synthesized by a typical sol-gel process using Al?NO₃?₃·9H₂O as raw materials.The density and the compressive strength of abrasive particles were measured and the average value was reported.The microstructure of sintered abrasive particles was investigated by field emission scanning electron microscopy.The average grain size and particle size distribution were calculated and analyzed.The temperature of the ?-Al₂O₃ to ?-Al₂O₃ phase transformation of the xerogel was also reported.The synergistic effect of additives and seeds on the sintering behavior and microstructural evolution in corundum abrasive were investigated.As to the SiO₂/ZnF₂ and TiO₂/La₂O₃ additive system,when the molar ratio of additives raised from 1:5 to 9:5,the grains changed from plate-like or sheet-like into equiaxed.In the La₂O₃/ZnF₂ system,the grains stayed in the shape of sheet while the molar ratio of additives raised.As to the La₂O₃/SiO₂ system,the grains were always equiaxed,and the average particle sizes are much smaller.Meanwhile the mechanical properties are also better.When the molar ratio of La₂O₃/SiO₂ was 5:5,the single particle compressive strength of the sample obtained the maximum value of 55.5N.In the additive system of TiO₂/SiO₂/La₂O₃,when the molar ratio of its two compositions SiO₂ and La₂O₃ is 5:5,the grain size distribution is more uniform,and the single particle compressive strength is also relatively higher.Specifically,when the proportion of TiO₂/SiO₂/La₂O₃ reached 6:5:5,the single particle compressive strength of the sample was as high as 58.9N.As to the system of TiO₂/La₂O₃/ZnF₂,when the molar ratio of its two compositions La₂O₃ and ZnF₂ ratio is 5:5,the grains were plate-like or sheet-like.When it is 3:5,the grains were in the shape of the equiaxed grains.When the molar ratio of TiO₂/La₂O₃/ZnF₂ is 27:15:25,the most uniform microstructure was obtained,and the single particle compressive strength was also the maximum value of 35.1N.Significant improvement of microstructural homogeneity,densification and mechanical property were achieved by the co-doping and two step sintering?TS?for the abrasive samples.All the doped samples showed relative densities higher than 98% and single particle compressive strength larger than 30 N.Besides,the two-step sintering samples attained much smaller particle sizes,slightly higher densities,and narrower particle size distributions.With MgTiO₃ seed and the addition of ZnF₂,TiO₂,SiO₂,fixed at 3 wt% and in the molar ratio of 5:7:5,the samples sintered by TS method obtained 56.3 N of single particle compressive strength,99.4% of theoretical density and 0.46 ?m of average grain size.The phase transformation temperature of doped samples were much lower than that of un-doped ones and it dropped significantly as the content of ZnF₂ raised.The relationship between microstructure and mechanical properties was also discussed.