【作者】 章德铭；

【导师】 李风珍；

【作者基本信息】 哈尔滨理工大学 ， 材料学， 2003， 硕士

【摘要】 采用反应铸造的方法，利用感应加热、坩锅熔炼及使用覆盖剂保护，制备原位TiC_p／Fe复合材料。利用光学显微镜、XRD、SEM等测试手段对复合材料的微观组织和相结构进行了分析和研究。对复合材料的制备工艺及工艺参数进行了系统的试验；在优化工艺的基础上，初步探讨了TiC颗粒在Fe-Ti-C熔体中的形成机制；对TiC_p／Fe复合材料在不同热处理工艺下的基体组织与性能进行了比较分析；对复合材料的机加性能和可焊性进行了试验研究。通过正交试验设计，摸索出了熔炼制备原位TiC_p／Fe复合材料的优选工艺方案为：w_C=2.8％，w_Si=1.0％，w_Ti=8.0％，反应温度为1650℃，保温10min。得到复合材料性能：HRC为46.8，α_k为14.25J·cm^-2；铸态组织为：在珠光体基体上，均匀分布着大量细小弥散的TiC颗粒。根据热力学及动力学分析，认为在碳颗粒界面处TiC的形核率很高，形核驱动力足以在正常的熔炼温度下形成众多的小晶核；熔体中TiC颗粒的合成可分为形核与长大两个阶段，其形核机制为：首先活性Ti原子包围C，溶入合金中的Ti与C在碳表面形成一复杂反应中间层，随着反应进行，Ti和C颗粒不断减少，生成的TiC不断弥散分布于熔体中；其长大过程伴随着TiC颗粒的相互堆砌、聚集和形态规则化。通过不同的热处理工艺可明显改变原位TiC_p／Fe复合材料的基体组织，但不改变TiC增强相的形态、尺寸及数量。退火处理使材料的硬度降低，韧性提高，便于机械加工；淬火+低温回火处理使材料的强度和硬度提高，而韧性无明显的降低；采用等温淬火工艺，可使TiC_p／Fe复合材料具有最好的综合机械性能。在本试验条件下，原位TiC_p／Fe复合材料切削加工时的切削力与45^#钢相比要大60N，切削温度要高90℃，加工表面粗糙度与45^#钢相近；TiC陶瓷颗粒使原位TiC_p／Fe复合材料切削加工时的切削力增大、切削温度增高，对加工表面粗糙度影响不大；原位TiC_p／Fe复合材料的可加工性与45^#钢相当。原位TiC_p／Fe复合材料采用不同焊接工艺和焊接方法所得的焊缝组织有所差别，但焊缝处的组织均匀，没有裂纹等焊接缺陷产生，可焊性较好；焊缝处的TiC增强颗粒仍保持铸态组织中TiC增强颗粒的形态。更多还原

【Abstract】 In-situ TiCp/Fe composites were prepared by reaction cast method with induction heating, crucible smelting and covering agent. The microstructure and phase structure of the composites were investigated by means of optional microscope, XRD and SEM. The preparation process and its parameters of composites were tested systemically. The forming mechanism of TiC particles in Fe-Ti-C melt was discussed preliminarily on the condition of optimized technology. The mechanical properties of TiCp/Fe composites with different microstructure were analyzed. The machinability and welding ability of the composites were also studied .The best process parameters of preparing TiCp/Fe composites were explored by means of orthogonal design test as: C was 2.8%, Si was 1.0%, Ti was 8.0% and reaction temperature was 1650 , heat preservation time was 10 minutes. The properties of the obtained composites were: HRC was 46.8, k was 14.25J cm-2. The cast microstructure was pearlite body with diffusion TiC particles distributed on it.According to thermodynamics and dynamics analysis, the forming-nucleus ratio of TiC was higher in the interface of carbon particles. The forming-nucleus drive power could form numerous little crystal nucleus under natural melting temperature. The formation of TiC particles in the melt could be divided into two phases which was forming-nucleus and growth. The forming mechanism of TiC was: melting Ti first surrounded C, then Ti melting in the alloy and C formed a complicated reaction mesosphere on the carbon surface. C particles decreased continually and the inborn TiC melted in the Ti liquid with the reaction. The growth process of TiC particles went with the pilling up, congregation and shape regularization of them.The microstructure and properties of TiCp/Fe in situ composites could be changed obviously by different heat treatments, however the shape, dimension and quantity of the TiC reinforcement couldn’t be changed. Annealing could reduce hardness and raise toughness, which could be prone to mechanical machining.Quenching and low temperature tempering could raise intensity and hardness of materials, not reduce toughness obviously. Quenching on same temperature caused TiCp/Fe in situ composites having the best integral machine properties.On the condition of the test, the cutting force of TiCp/Fe composites was morethan which of 45 steel by 60N, and the cutting temperature was higher than which of 45# steel by 90 , and the roughness of machined surface was almost as much as which of 45# steel. TiC ceramic particles enhanced the cutting force and the cutting temperature of TiCp/Fe composites, but had little effect on the roughness of machined surface. The machining quality of TiCp/Fe in situ composite was similarity to 45# steel.The welding line microstructure of TiCp/Fe in situ composites gained by different welding technologies and welding methods was different. However the microstructure was diffused on the welding line and there were no welding defects, the welding quality was better. The TiC reinforced particles on the welding line still kept the same shape as that of the casting microstructure.更多还原