【作者】 张士察；

【导师】 温广武；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2009， 硕士

【摘要】 本文采用反应热压烧结的方法,以纳米级氧化锆(微米级氧化锆)、氧化铝、硼酸、氮化铝为原料,制备了具有良好可加工性能的ZTA/BN复相陶瓷材料。利用XRD、SEM、TEM等分析手段,对复相陶瓷材料的物相组成、组织结构进行了分析、观察。研究了该复相陶瓷的制备工艺、力学性能以及可加工性能,并对该复相陶瓷的高温氧化行为及表面裂纹修复进行了初步探索。研究结果表明随BN含量的增加,复相陶瓷材料的致密度和力学性能逐渐下降,而可加工性能得到提高。而随烧结温度的提高,ZTA/BN复相陶瓷材料的致密度、力学性能均得到大幅度的提高。在1800℃的烧结温度下,使用纳米级氧化锆的nm-ZTA/12.5%BN复相陶瓷材料的抗弯强度和断裂韧性分别达到731MPa和7.48MPa·m1/2,同时具有可加工性。SEM结果表明,通过反应热压烧结,在氧化锆及氧化铝晶粒之间有大量的团簇状的BN片晶生成,片宽500nm左右,片厚50nm左右。这种BN片晶的生成,能发挥BN层状结构可分散裂纹尖端应力集中的特点,有助于改善材料的力学性能。同时,低模量h-BN的引入,降低了材料的弹性模量,由于纳米尺寸的h-BN在基体中的均匀分散,处于晶界出的BN片晶相当于在基体相晶粒之间引入微裂纹。在材料加工时,分散的微裂纹区域扩展,相互连接导致通过个别粒子的移位而去除材料,从而提高复相陶瓷材料的可加工性能。试样的TEM观察从微观角度解释了反应热压体系为什么能有效抑制在烧结降温过程中氧化锆发生t→m相变。氧化锆主要以t相形式存在,与XRD结果向吻合。利用常规的磨削和钻孔方法对ZTA/BN复相陶瓷材料进行了可加工试验。使用钻孔速率及可加工指数对复相陶瓷材料的可加工性能进行了评价。更多还原

【Abstract】 ZTA/BN composite ceramics were prepared via in-situ synthetic reaction in order to develop a new machinable material in this thesis. Nano-scale or micron-scale zirconia, alumina, boric acid and aluminum nitride were used as raw materials. The phase composition, organizational structure of muti-phase ceramics were analyzed and observed using XRD, SEM, and TEM. Preparation methods, mechanical properties and machinability of the muti-phase ceramics were studied. At the same time, high-temperature oxidation behavior and repairing of surface crack were explored preliminarily.The results show that with the increase of BN content, the density and mechanical properties decrease, whereas machinability is enhanced. While with the increase in sintering temperature, the density, mechanical properties of ZTA /BN composite ceramics are significantly improved. In the sintering temperature of 1800℃, the flexural strength and fracture toughness of nmZTA/12.5%BN composite ceramics reach 731MPa and 7.48MPa·m1/2, with machinability.SEM results show that via in-situ synthetic reaction, a large number of cluster shape and flake-like BN were generated between grains of zirconnia and alumina, with about 500nm wide and 50nm thick around. Because of this generation of flake-like BN, stress concentration of crack tip can be dispersed via BN layered structure, helping to improve the mechanical properties of materials. At the same time, low modulus of the introduction of h-BN, the elastic modulus of the material was reduced. As a result of the uniform dispersion of nano-sized h-BN in the matrix, flake-like BN in the grain boundary is equivalent to introducing micro-cracks between grains of matrix phase. In material processing, the dispersion of regional expansion of the micro-cracks and mutual connection, lead to the removal of material by the displacement of individual particles, consequently machinability was enhanced of the composite ceramics.TEM observation of samples explained from the micro perspective why the reaction hot-pressing system can effectively inhibit the t→m phase transformation of zirconia occurred in the course of decreasing temperature. Zirconia phase mainly existed in the form of t-ZrO2, coinciding with the XRD results.Machinable experiment of ZTA/BN composite ceramics was carried out using conventional methods of grinding and drilling, and Machinability was evaluated by drilling rate.更多还原