【作者】 徐亮；

【导师】 黄传真；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2013， 博士

【摘要】 本文针对传统热压烧结陶瓷刀具制备工艺的局限性,提出了原位一体化制备棒晶增韧陶瓷刀具的设计思路,研制了TiB2棒晶增韧TiB2-TiCx基复合陶瓷刀具材料和ZrB2棒晶增韧ZrB2-ZrCx基复合陶瓷刀具材料。对陶瓷刀具的力学性能、物相组成、微观组织、棒晶的生长机理、陶瓷刀具的致密化机理、增韧机理、切削性能和磨损可靠性进行了系统的研究。原位一体化制备棒晶增韧陶瓷刀具的研制成功拓展了陶瓷刀具材料制备工艺,并为高性能陶瓷刀具的开发奠定了理论与应用基础。提出了基于过渡塑性相方法的原位一体化制备棒晶增韧陶瓷刀具的材料组份设计方案。利用过渡塑性相方法、Ti-B-C与Zr-B-C三元相图选取Ti-B4C与Zr-B4C为反应体系,研制了TiB2棒晶增韧的TiB2-TiCx基复合陶瓷刀具材料和ZrB2棒晶增韧的ZrB2-ZrCx基复合陶瓷刀具材料。对反应体系的热力学分析表明,所选反应体系属于反应可自发进行、可自维持的放热反应体系。提出了基于热爆SHS(Self-propagating High-temperature Synthesis, SHS)-加压辅助致密化的原位一体化制备棒晶增韧陶瓷刀具的制备工艺。结合热爆炸理论、晶体学原理和烧结实验对原位一体化制备工艺中的点火方式、点火温度、延时时间、延时压力和烧结温度等工艺参数进行优化。研究了原位一体化制备棒晶增韧陶瓷刀具的制备工艺和力学性能。研制了TBw(TiB2棒晶/TiB2/TiCx)和ZBw(ZrB2棒晶/ZrB2/ZrCx)两种新型陶瓷刀具材料。研究表明,反应体系在Ti/B4C=4/1的摩尔配比下,当烧结温度为1750℃,保温时间为60min,延时时间为5s,延时压力为16MPa,保压压力为35MPa时TBw刀具材料的力学性能最优,即抗弯强度为890.3MPa,断裂韧度为7.5MPa·m1/2,维氏硬度为20.6GPa,相对密度为99.3%。反应体系在Zr/B4C=4/1的摩尔配比下,当烧结温度为1750℃,保温时间为60min,延时时间为5s,延时压力为16MPa,保压压力为35MPa时ZBw刀具材料的力学性能最优,即抗弯强度为898.1MPa,断裂韧度为9.1MPa·m1/2,维氏硬度为17.6GPa,相对密度为98.2%。研究了陶瓷刀具力学性能、物相组成与微观组织之间的关系。研究了原位一体化制备中棒晶的生长机理、陶瓷刀具材料的致密化机理和增韧机理。建立了棒晶生长的异向Ostwald Ripening生长模型和陶瓷刀具材料微观组织演变模型。研究表明,棒晶的生长机理一方面与其晶体结构的固有属性相关。另一方面,棒晶首先以非平衡熟化形核过程析出晶核并初步生长；当整个体系的过冷度逐渐降低时,棒晶以平衡熟化生长过程继续生长并在保温阶段发育完全。对TBw和ZBw刀具的致密化机理研究表明,反应体系的摩尔体积、过渡塑性相TiCx与ZrCx含量和其包含的C原子空位、过渡塑性相的高温屈服行为和金属液相的润湿性均影响反应体系的相对密度。对TBw和ZBw刀具的增韧机理研究表明,在刀具基体内均匀分布且随机取向的棒晶起到了类似晶须的增韧作用,主要包括裂纹偏转、棒晶桥联及棒晶拔出等。棒晶形成的互锁结构、板晶、晶须、晶粒表面的纳米颗粒阵列等均对陶瓷刀具材料有一定的增韧贡献。研究了TBw刀具连续干切削奥氏体不锈钢1Cr18Ni9Ti时的刀具切削性能和刀具磨损可靠性。结果表明,当切削速度为60m/min,进给量为0.1mm/r,切削深度为0.1mm时,TBw刀具的磨损寿命最高,刀具的抗磨损能力由强到弱的顺序为TBw>LT55>ZBw>SG4。在低速下,TBw刀具的主要磨损机理是磨粒磨损、扩散磨损和氧化磨损。在高速下,TBw刀具的主要磨损机理是磨粒磨损、粘结磨损、扩散磨损和氧化磨损。TBw刀具的磨损寿命服从伽马分布,刀具磨损寿命在该切削用量下的磨损可靠度为46.54%。当磨损可靠度为90%时,刀具磨损可靠寿命为8.71min。TBw刀具的磨损寿命变异系数为0.155,因此该刀具的磨损可靠性良好。研究了ZBw刀具连续干切削奥氏体不锈钢1Cr18Ni9Ti时的刀具切削性能和刀具磨损可靠性。结果表明,当切削速度为40m/min,进给量为0.1mm/r,切削深度为0.1mm时,ZBw刀具的磨损寿命最高,刀具的抗磨损能力由强到弱的顺序为ZBw>LT55>TBw>SG4。在低速下,ZBw刀具的主要磨损机理是磨粒磨损和氧化磨损。在高速下,ZBw刀具的主要磨损机理是磨粒磨损、扩散磨损和氧化磨损。ZBw刀具的磨损寿命服从对数正态分布,刀具磨损寿命在该切削用量下的磨损可靠度为36.51%。当磨损可靠度为90%时,刀具磨损可靠寿命为12.53min。ZBw刀具的磨损寿命变异系数为0.1099,因此该刀具的磨损可靠性良好。更多还原

【Abstract】 Aimed at the limitations of fabrication process of the ceramic tools prepared by the hot-pressing sintering technology, the design scheme for the in-situ integrative fabrication of ceramic tools toughened by the elongated grains was proposed. Moreover, the TiB2-TiCx ceramic tools toughened by the elongated TiB2grains and the ZrB2-ZrCx ceramic tools toughened by the elongated ZrB2grains were fabricated successfully. The mechanical properties, phase composition, microstructure, growth mechanism of the elongated grains, densification and toughening mechanism, cutting performance and cutting reliability were studied systematically. The research results enhanced the application domain of the preparation technology of the ceramic tools and laid the theoretical and application foundation for the future development of ceramic tools with higher mechanical properties.The material components and the reaction system were designed based on the transient plastic phase process and the Ti-B-C/Zr-B-C ternary phase diagram. The Ti-B4C was chosen as the reaction system to synthesis TiB2-TiCx ceramic tools toughened by the elongated TiB2grains and the Zr-B4C was chosen as the reaction system to synthesis ZrB2-ZrCx ceramic tools toughened by the elongated ZrB2grains. The thermodynamic calculations on Ti-B4C and Zr-B4C systems indicated that the reactions were spontaneous, self-propagating and exothermic. The fabrication process was proposed based on the SHS(Self-propagating High-temperature Synthesis, SHS) method, which was ignited by the thermal explosion method. According to the theory of thermal explosion and crystallography, the experiment optimization focused on the ignition method, ignition temperature, delay time for the pressure, the pressure after the delay time and the sintering temperature, etc. The fabrication process and the mechanical properties of the ceramic tools toughened by the elongated grains were studied. The TBw(the elongated TiB2grains/TiB2/TiCx) and ZBw(the elongated ZrB2grains/ZrB2/ZrCx) ceramic tools were developed successfully. When the molar ratio of Ti/B4C is4/1, the sintering temperature is1750℃, the duration time is60min, the delay time is5s, the pressure after delay time is16MPa and the final pressure is35MPa, TBw had the highest comprehensive mechanical properties. The flexural strength, fracture toughness, Vickers hardness and relative density are890.3MPa,7.5MPa·m1/2,20.6GPa and99.3%, respectively. When the molar ratio of Zr/B4C is4/1, the sintering temperature is1750℃, the duration time is60min, the delay time is5s, the pressure after delay time is16MPa and the final pressure is35MPa, ZBw had the highest comprehensive mechanical properties. The flexural strength, fracture toughness, Vickers hardness and relative density are898.1MPa,9.1MPa·m1/2,17.6GPa and98.2%, respectively. The relationship among the microstructure, phase composition and mechanical properties was investigated.The anisotropic grain growth mechanisms during the in-situ fabrication process, densification and toughening mechanism of ceramic tools were studied. There were two aspects for the growth mechanism of the elongated grains. The first one is involved in the inherent crystallographic orientation of TiB2and ZrB2.The other one is that the nonequilibrium ripening nucleation process controlled the nucleation and initial growth of the elongated grains. With the decrease in the degree of supercooling, the growth of elongated grains was dominated by the equilibrium ripening growth process and developed completely during the duration time. The densification was attributed to the volume changes during the reaction, the content of carbon vacancies in the non-stoichiometric phases (TiCx and ZrCx), the wetting of the liquid to the matrix and the high temperature yield behavior of TiCx and ZrCx. The toughening mechanisms with the discontinuous elongated grains were crack deflection, bridging and grain pullout. The interlocking structures, platelets, whiskers and the nanoparticles array on the surface of the grains improved the toughness accordingly. The cutting performance and tool wear reliability of TBw ceramic tools in dry machining stainless steel1Cr18Ni9Ti was studied. The highest tool wear life of TBw was obtained when the cutting speed is60m/min, the feed rate is O.lmm/r and the depth of cut is0.1mm. The main tool wear mechanisms of TBw were abrasive wear, diffusion wear and oxidation wear at a low cutting speed. The main tool wear mechanisms of TBw were abrasive wear, diffusion wear, oxidation wear and adhesion wear at a high cutting speed. The Gamma distribution was appropriate for modeling the tool wear life of TBw. The reliability of the tool wear life (11min) is46.54%. The reliable tool wear life of TBw is8.71min when the wear reliability was90%. The variation coefficient of wear life is0.155, thus the tool wear reliability of TBw is good.The cutting performance and tool wear reliability of ZBw ceramic tools in dry machining stainless steel1Cr18Ni9Ti was studied. The highest tool wear life of ZBw was obtained when the cutting speed is40m/min, the feed rate is0.1mm/r and the depth of cut is0.1mm. The main tool wear mechanisms of ZBw were abrasive wear and oxidation wear at a low cutting speed. The main tool wear mechanisms of ZBw were abrasive wear, diffusion wear and oxidation wear at a high cutting speed. The Lognormal distribution was appropriate for modeling the tool wear life of ZBw. The reliability of the tool wear life (15min) is36.51%. The tool reliable wear life of ZBw is12.53min when the wear reliability was90%. The variation coefficient of wear life is0.1099, thus the tool wear reliability of ZBw is good.更多还原