【作者】 杨涛；

【导师】 李志宏； 翟涵；

【作者基本信息】 天津大学 ， 材料工程（专业学位）， 2017， 硕士

【摘要】 陶瓷刚玉磨料具有较传统熔融刚玉磨料更小的,微米、亚微米级的晶粒尺寸及更为均匀的显微结构,因此具有更为优异的自锐性、韧性、加工效率、加工精度及使用寿命等性能,已经在各领域的磨削加工上广泛应用。本实验通过Sol-Gel工艺制备前驱体,再经烧结得到陶瓷刚玉磨料。实验从制备特定晶粒形貌的陶瓷刚玉磨料出发,研究了不同添加剂体系及烧结制度对陶瓷刚玉磨料显微结构及性能的影响。实验结果表明:添加Na₃AlF₆可以得到片状晶陶瓷刚玉磨料。陶瓷刚玉磨料的显微结构受到Na₃AlF₆的含量及烧结温度的显著影响。在1300 ^oC以下,片状晶的发育随Na₃AlF₆的含量增加而更完全。在烧结温度为1400 ^oC及Na₃AlF₆的含量为2.5 wt%时,片状晶发育最好。CaO/SiO₂、MgO/SiO₂二元添加剂及MgO/CaO/SiO₂三元添加剂可以通过液相烧结机理促进烧结,从而显著提高陶瓷刚玉磨料的抗压强度,同时其对显微结构也具有明显影响。在添加Na₃AlF₆的基础上,加入以上添加剂,发现添加CaO:SiO₂=1:1和MgO:SiO₂=1:2时,晶粒保持片状,但尺寸及径厚比减小;添加CaO:SiO₂=2:5和MgO:SiO₂=1:3时,晶粒变为不规则的片状;添加MgO:CaO:SiO₂=1:3:6时晶粒的尺寸小且保持规则片状,同时烧结致密度高,综合性能最佳。陶瓷刚玉磨料的显微结构与性能也受到烧结制度的显著影响。对上述体系添加剂的试样进行二步烧结,随着二步烧结中第二步烧结温度的升高,片状晶粒的规则度及烧结的致密度越来越高。在1400 ^oC-1300 ^oC/2 h的二步烧结中,陶瓷刚玉磨料的性能最佳。通过ZnF₂-TiO₂-La₂O₃三元添加剂的协同作用,可以得到一种新颖的截顶立方体状晶陶瓷刚玉磨料。其由α-Al₂O₃主晶相及La₄Ti₃O₁₂和La Al₁₁O₁₈次晶相构成。截顶立方体状晶粒的TEM、HRTEM及SAED分析结果,同时结合晶体结构计算,表明其为α-Al₂O₃晶粒且晶粒表面属于{012}晶面族,截顶面为（001）晶面。截顶立方体状晶的生长过程研究,表明其生长机理为截顶面上的二维成核生长。同时,说明ZnF₂-TiO₂-La₂O₃三元添加剂协同作用导致{012}晶面族具有最低的表面能。更多还原

【Abstract】 Ceramic alumina abrasives possess micrometer or submicrometer sized grains and a uniform microstructure,therefore superior processing efficiency,finish quality and service life,have been widely used in many fields.In this work,ceramic alumina abrasives were prepared through a Sol-Gel and sintering process.Focusing on grain morphology control,the effect of additives and sintering procedure on the microstructure and mechanical properties were studied.The results are as follows.Ceramic alumina abrasives with a platelet grain morphology can be synthesized with Na₃AlF₆ addition.Both Na₃AlF₆ content and sintering temperature have a significant impact on the microstructure.When sintering temperature is below 1300^oC,the platelet grains are better developed with increasing Na₃AlF₆ content.While sintering at 1400 ^oC with 2.5 wt%Na₃AlF₆ addition leads to the best developed platelet grains.CaO/SiO₂,MgO/SiO₂ binary additives and MgO/CaO/SiO₂ ternary additives can promote sintering through liquid phase sintering mechanism,thus significantly improve the strength of ceramic abrasives.They have an impact on the grain morphology as well.Based on Na₃AlF₆ addition,the introduction of CaO/SiO₂ and MgO/SiO₂ additives at a molar ratio of 1:1 and 1:2 respectively lead to smaller grain size and smaller aspect ratio while preserving platelet morphology.When the introduced CaO/SiO₂ and MgO/SiO₂ additives are at a molar ratio of 2:5 and 1:3respectively,the grain shape became irregular.With MgO/CaO/SiO₂ ternary additives of molar ratio 1:3:6,the samples reached optimal properties of smaller platelet grain size and high density.Sintering procedure also has a profound influence on the microstructure and properties.When sintering aforementioned samples with two-step sintering method,the platelet grains are better developed and density increased with increasing temperature of the second step.Two-step sintering of 1400-1200 ^oC/2 h gives best performance.Ceramics alumina abrasive with a novel truncated cube grain morphology can be synthesized with Zn F₂-Ti O₂-La₂O₃ ternary addition.XRD results showed the samples consist ofα-Al₂O₃ as major phase and two minor phases of La₄Ti₃O₁₂ and LaAl₁₁O₁₈.TEM,HRTEM and SAED analysis,together with structural calculation,indicate the truncated cube grains are covered with planes from{012}plane family and（001）plane as the truncated face.Grain growth study showed the growth mechanism of the truncated cube grains is two dimensional nucleation and growth on the（001）plane.These results also indicate the synergistic effect of ZnF₂-TiO₂-La₂O₃ ternary addition leads to{012}plane family has the lowest surface energy.更多还原