高性能定向织构化Ti2AlC/Mg基复合材料制备及各向异性特征机理研究

For the performance requirements of high specific strength, high specific modulus, high damping and wear resistance in Mg based composites applications, this project explores a preparation method to obtain oriented texturing Mg matrix composites based on the ternary Ti2AlC MAX phase as nucleating agent and reinforcement. The first step is to fabricate and optimize the Ti2AlC/Mg composite with Ti2AlC uniform distribution through powder metallurgy. Concerning about this part, we focus on the formation mechanism of oriented nano-Mg grains on Ti2AlC surfaces and the relationship between mechanical strength and damping properties in reference to the Ti2AlC volume fraction in the composites. The second step is to realize the texture orientation in Ti2AlC/Mg composite by hot extrusion method. Concerning about this part, we study the influence of Ti2AlC with different aspect ratios on the textured orientation in composites. Above all, the relationship between textured microstructure and mechanical properties, damping properties, electrical properties, friction properties would be given the full consideration. Through this study, the effect of Ti2AlC grain orientation on composite microstructure and physical properties is anticipated to be explained. Furthermore, the resolutions of the above scientific questions could provide a reference and science inspiration for the application of the texture-orientated Ti2AlC-Mg composite, and also for the other similar composites.

针对Mg基复合材料应用中高比强度、高比模量，高阻尼减震和耐磨特性的性能需求，本项目以三元Ti2AlC MAX化合物为增强体，探索制备高性能定向织构化的Ti2AlC-Mg基复合材料。第一步，采用粉末冶金方法制备组织均匀的Ti2AlC-Mg基复合材料；研究复合材料界面处纳米Mg晶粒的形核机制；择优选取具备优良强度-阻尼性能的Ti2AlC-Mg基复合材料。第二步，采用热挤压工艺实现Ti2AlC-Mg基复合材料的组织定向织构化；研究具有纵横比的Ti2AlC晶粒对复合材料定向织构化的作用；研究材料组织与力学性能、阻尼性能、电学性能和摩擦性能的关系并建立物理模型。通过本项目的研究，阐明Ti2AlC晶粒定向对复合材料结构控制和物理性能作用机理等关键问题，为该复合材料和其他类似复合材料的制备和应用提供借鉴和理论参考。

系统开展了定向织构化Ti2AlC-Mg基复合材料的微观组织和力学，阻尼及摩擦性能研究。原位拉伸实验表明材料裂纹产生于Ti2AlC颗粒内部，而不是Ti2AlC与Mg基体的界面。球差透射表明Ti2AlC中的Al原子扩散到Mg基体中。铸态的Ti2AlC-AZ91D镁基复合材料进行热挤压后，样品中出现晶粒再结晶现象，一部分亚微米级与纳米级的Ti2AlC和析出相Mg17Al12晶粒弥散到Mg晶粒中。由于Ti2AlC颗粒在热挤压后发生了重新取向，拉伸和压缩试验证明织构化复合材料的各向异性比织构化AZ91D合金更强。同时，我们提出了不同的断裂机理。此外//ED和⊥ED试样电阻率随温度的斜率（dρ/dT）和电阻率比R293K/R77K（RRR）的变化证实了Ti2AlC对AZ91合金中自由电子散射的影响。阻尼实验表明复合材料具有更好的阻尼容量，复合材料室温以及高温阻尼容量随Ti2AlC增强相体积分数的增加而增加。高低温动态弹性模量表明增强体Ti2AlC的加入可以强化材料。与SiC-Mg基体复合材料出现“犁沟”不同，Ti2AlC-Mg基复合材料表现出优良的耐磨自润滑特性。复合材料的自润滑性能来自于镁基体氧化和Ti2AlC MAX相的自润滑贡献。同时，复合材料都表现出优于AZ91D镁合金的耐磨性能和自润滑性能。此外，实验表明织构化Ti2AlC-Mg复合材料摩擦学性能具有各向异性特征。