【作者】 陈新华；

【导师】 翟洪祥；

【作者基本信息】 北京交通大学 ， 载运工具运用工程， 2013， 博士

【摘要】 采用陶瓷颗粒增强的方法可以提高金属材料的刚度、比强度、耐磨损、耐冲击、抗蠕变等性能,在交通运输、核能、冶金机械等领域有着良好的应用前景。本研究通过原位反应型复合的常压制备技术和原位热挤压制备技术,成功制备出具有良好性能、可以满足一定工业应用要求的非化学计量比TiCx增强Fe基原位反应型复合材料。本论文以理论分析与实验研究相结合的研究方法,通过材料电子层次的理论设计、热力学与动力学反应机理分析、制备工艺参数影响、材料显微组织结构与宏观性能之间的强韧化规律等分析的技术路线,探讨了MAX-金属反应型复合材料的反应机理、制备工艺、显微组织结构及性能的基本规律,主要研究了如下内容：1,通过Ti3AlC2-Fe体系价电子理论和密度泛函理论研究,探讨了原位反应的本质,进而对复合材料的组分和界面等进行设计。2,研究了Ti3AlC2-Fe体系材料热力学、动力学反应机理以及高温下Ti3AlC2在Fe基体中拓扑转变行为。3,研究TiCx/Fe-Al材料的制备工艺参数、显微组织结构以及宏观性能的变化规律。以MAX相为先驱体制备非计量比MX/Fe-A体系反应型复合材料,可以克服传统陶瓷增强相所存在的界面润湿性差、增强相难以达到亚微米尺寸且分布均匀等难题,但也存在反应控制、结构调整等特色问题,需要对传统材料制备技术进行改进,从而实现所制备的复合材料具有良好的组织成分、显微结构与界面联接,使其性能能更充分发挥。本论文解决了如下主要关键问题：1,如何控制MAX相的分解,以获得TiCx增强相;2,如何实现对复合材料显微组织、结构调整问题；3,克服复合材料制备中致密化等工艺技术问题。在此基础上,揭示了材料的制备工艺、组织结构与宏观性能之间的基本规律关系,为进一步研制更高性能和更满足实际应用的非化学计量比陶瓷颗粒增强金属基复合材料提供了理论与实验依据。得到了如下主要结论：1, Ti3AlC2与Fe之间的原位反应机理,为Fe原子与A1原子之间成键能力较强,使Ti3AlC2中的Al原子析出并扩散到Fe中形成A1原子含量局域梯度变化的Fe-Al过渡层偏聚结构,而Ti3AlC2则转变成TiCx相。所制备的TiCx/Fe-Al复合材料中,最优界面为(110)Fe-A1的晶面与(100)Ticx的晶面联接。2, Ti3AlC2在Fe的环境中分解温度会降低,最终在复合材料形成反应产物为TiCx和Fe-Al,并表现出放热效应。Ti3AlC2-Fe体系的反应活化能为75.26kJ/mol。3, TiCx/Fe-Al制备的最优烧结温度为1300～1400℃,最优保温时间为30mins,原料中Ti3AIC2的含量应低于30vol.%。4, Fe-Ti3AlC2体系反应机制为原位反应-扩散-溃散-颗粒形成,反应后,所形成的TiCx颗粒厚度甚至只有50nm,且颗粒与基体界面洁净,联接较好。5,原位热挤压所制备15.61TiCx/Fe-Al样品的抗拉强度能达到666MPa,拉伸应变达到7%。在拉伸载荷的作用下,TiCx/Fe-Al材料的真应力真应变曲线可以分为四个强化阶段,并表现为非均匀变形。主要创新成果如下：1,通过价电子理论和密度泛函理论计算、材料设计、材料热力学和动力学研究,分析了Ti3AlC2与Fe之间的反应机理。2,基于上述分析和计算,制备出TiCx/Fe-Al块体材料。分析了高温条件下Ti3AlC2与Fe的反应机制,并初步得到透射电镜的证实。3,采用原位热挤压制备了TiCx/Fe-Al复合材料的抗拉强度达到666MPa,延伸率超过7%。更多还原

【Abstract】 Metal matrix composites (MMCs) have already attracted much attention for their potential applications in many fields such as nuclear energy, metallurgy, mining and traffic engineering industries where conventional alloy systems are not suitable. But, it is not easy to get a strong interface bonding between conventional reinforcements with metal matrix, and deal with the intractable problems of particles agglomerating caused by the lager surface activity by using conventional methods, such as casting and mechanical alloying. In addition, the preparation and the preservation are also difficult for sub-micron or even nanosize powders.By in situ reaction compound method, this work has prepared TiCx/Fe-Al composites through pressureless sintering technique and hot extrusion technique, which consists of nonstoichiometric TiCx particles and Fe-Al matrix and can fulfill many industrial applications requirements. The technology roadmap was adopted via EET and DFT, CALPHAD technique and thermal analysis, the optimum preparation process, mechanical properties and plastic behavior. The major research contents are as follows:1, Theoretical aided composite materials were designed at electronic and atomic scale by EET and DFT.2, Thermodynamic and thermal kinetics mechanism of Ti3AlC2-Fe investigated according to CALPHAD technique and thermal analysis, and the path of topotactic transformation of Ti3AIC2into TiCx in Fe matrix was judged.3, The relation between the preparation process, microstructure and performance were studied.Key problems have been solved:1, How to control the breakup of MAX and get TiCx phase.2, How to realize the adjustment of phase and microstructure in TiCx/Fe-Al composites.3, How to overcome the densification and other process problems during composites preparation.Main conclusions:1, The essence of the reaction is the bonding ability between Fe and Al is stronger than Ti-Al in Ti3AlC2, and lead to break down of Ti3AlC2into TiCx. The interface connection of (110)Fe-Al//(100)TiCx is preferably. 2, Ti3AlC2can topotactic transform into TiCx in Fe matrix, those reactions are exothermic and their decalescence about75.26kJ/mol.3, The optimal sintering temperature of1300-1400℃, the optimal soaking time are30mins, and Ti3AlC2contents in starting materials are better below30vol.%.4, Reaction scheme of Fe-Ti3AlC2system can be divided into4steps:In situ reactions-Diffusion-Collapsing-Further decomposed; The TiCx grains generated possess a platelike shape with about50nm in thickness, and the grain boundary between the TiCx grain and matrix is clear and no interface phase can be found.5, The prepared material exhibited a higher tensile strength of about666MPa and a uniform deformation of about7%.The innovations of this work can be drawn mainly as follows:1, Systematic investigations were done on the fabrication and microstructural characterization of TiCx/Fe-Al composites by pressureless sintering technique and hot extrusion technique.2, Systematic investigations were done on the reaction mechanism between Ti3AIC2and Fe, and the results have initially been confirmed by TEM.3, Systematic investigations were done on the mechanical and electrical properties of TiCx/Fe-Al composites by pressureless sintering technique and hot extrusion technique. The prepared material exhibited a higher tensile strength of about666MPa and a uniform deformation of about7%.更多还原