自生TiB2-TiCx/Al复合材料在含硫、氮气氛下的高速磨损—腐蚀失效机制

Piston would be suffered high temperature wear containing corrosive atmosphere such as SOx, NOx during its operation, which could incur its life shorten. With the reinforcement improvement of internal combustion engine, the working condition of the piston would become worse, so the piston material properties and friction failure analysis would be put forward higher requirements. The project is based on the design concept of the in-situ synthesized second phase and double reinforcing phase complementary, proposes the principle of preparation of 7075 aluminum matrix composites reinforced by in-situ TiB2-TiCx through self-propagating reaction induced by mechanically alloying technology. The composite's mechanical proparties and wear performance under special atmosphere containing SOx, NOx and Ar during 25℃~430℃ in oil lubrication, boundary lubrication and dry friction conditions are explored. Combined with its friction coefficient, wear rate，worn surface and subsurface morphology analysis, the wear mechanisms are summarized. By carrying out the project, the high speed wear-corrosion mechanism of aluminum matrix composites under special atmosphere containing SOx and NOx are explored, meanwhile, theoretical basis and technical support are provided.

活塞在运行过程中遭受含SOx、NOx等腐蚀气氛的高温高速磨损，对其寿命影响较大。随着内燃机强化程度的提高，活塞的工作状况将变得更加恶劣，从而对活塞所用材料的综合性能与严酷工况下的高速磨损失效分析提出了更高的要求。本项目以原位自生第二相强化为设计思想，以两种增强相互补为设计原则，采用机械合金化诱发自蔓延反应与热压烧结相结合的方法原位合成自生增强TiB2-TiCx/7075Al复合材料，通过热挤压技术进一步改善其微观组织和宽温域力学性能。对综合性能较优异的材料在室温~430℃含SOx、NOx气氛与Ar气保护气氛下油润滑、边界润滑与干摩擦工况的摩擦学行为进行探索，结合摩擦因数、磨损率、磨损表面和亚表层形貌与成分分析等深入探讨其磨损失效机制。该项目的实施可阐明TiB2、TiCx双相增强7075Al复合材料在含SOx、NOx特殊气氛下的高速磨损—腐蚀失效机制，为高性能铝基复合材料的研发提供理论依据。

活塞在运行过程中遭受含SOx、NOx等腐蚀气氛的高温高速磨损，对其寿命影响较大。随着内燃机强化程度的提高，活塞的工作状况将变得更加恶劣，从而对活塞所用材料的综合性能与严酷工况下的高速磨损失效分析提出了更高的要求。本项目从铝基复合材料的组配设计、制备工艺优化入手，采用机械合金化诱发自蔓延反应与热压技术相结合的手段制备原位自生增强TiB2-TiCx/7075复合材料，探讨自生TiB2-TiCx增强相对铝基复合材料组织、结构、性能的影响，阐明铝基复合材料在含硫/氩气保护气氛不同工况条件下高速宽温域的摩擦磨损机制，最终获得兼顾优异力学和摩擦学性能的新型铝基复合材料。该研究表明，经机械合金化一定比例的7075Al、Ti、B4C并诱发其发生自蔓延反应成功制备自生TiB2-TiCx/7075复合材料粉体，后期通过适宜热压烧结工艺制备不同增强相含量的TiB2-TiCx/7075复合材料、VN/7075复合材料及多相(VN, TiB2-TiCx)/7075复合材料。磨损测试结果表明：高温下材料的磨损机制为黏着磨损，少量磨粒磨损和氧化磨损并存。大气气氛较氩气气氛下，材料的摩擦因数较低，这是由于高温下大气气氛磨损表面氧化层的出现改善了材料的耐磨性。不同工况下，几种材料的摩擦因数和磨损率均呈现：干摩擦＞含硫边界润滑＞油润滑。随着VN含量的增加，单相VN/7075复合材料的体积磨损率均呈现先减小后增大趋势，VN含量为15wt.%时，各工况下其体积磨损率达到最小，且含硫边界润滑工况下的摩擦因数和磨损率与油润滑相当。多相(VN, TiB2-TiCx)/7075复合材料的摩擦磨损性能较好，归因于磨损过程中磨损表面自生成一层可改善其耐磨性的自润滑膜(主要成分为(SN)x和VSx)，且有较高的强度、硬度的基体对该层润滑膜有良好的支撑，因此其摩擦因数和磨损率均较低，磨损机理主要为磨粒磨损。经过ECAP挤压后15wt.% VN/7075铝基复合材料在磨损过程中形成的表层润滑膜更为致密，磨损性能得以显著改善。该项目的实施可阐明TiB2、TiCx双相增强7075Al复合材料在含硫等特殊气氛下的高速磨损—腐蚀失效机制，为高性能铝基复合材料的研发提供理论依据和技术支撑。