【作者】 山泉；

【导师】 蒋业华； 李祖来；

【作者基本信息】 昆明理工大学 ， 材料加工工程， 2013， 博士

【摘要】 随着现代工业的发展,越来越多的零部件需要在复合磨损工况下服役,其中激冷激热与磨损复合工况成为冶金、机械等领域研究和应用的热点。陶瓷颗粒增强钢基表层复合材料利用了金属基体良好的塑韧性和陶瓷颗粒的高硬度,表现出较好的耐磨性,但其在激冷激热等存在热冲击作用的工况下又表现出抗热疲劳性能较低的劣势,由此可见,陶瓷颗粒增强钢基表层复合材料在激冷激热工况下的热疲劳行为成为急需研究的重要课题。论文利用自制的铸渗装置成功制备了碳化钨颗粒增强钢基表层复合材料(碳化钨/钢基表层复合材料),通过组织分析、热物理性能测试、热疲劳行为观察及热力学和力学计算等,重点研究了表层复合材料组织与热物理性能间的关联、复合材料的热疲劳裂纹萌生和扩机制等内容。研究了碳化钨/钢基表层复合材料的组织与热物理性能(热膨胀系数、比热、热扩散系数、热导率)之间的关联。结果表明：(1)表层复合材料复合层组织由WC、W2C、Fe2W2C、Fe3W3C、Cr7C3及马氏体组成：(2)沿复合层与基材间宏观界面至复合层表面方向,碳化钨颗粒的体积分数逐渐增大,而其热膨胀系数、比热、热扩散系数、热导率却呈降低趋势；(3)随着碳化钨颗粒尺寸的增大,表层复合材料的热膨胀系数、比热、热扩散系数、热导率呈降低趋势。(4)表层复合材料的热膨胀系数曲线在630℃以下波动较小,随着碳化钨颗粒尺寸的减小,表层复合材料的热稳定性有所提高,在温度小于630℃时表现出较高的热稳定性。通过实验观察并结合热力学计算,对表层复合材料进行抗氧化性和热疲劳行为研究。结果表明：(1)碳化钨/钢基表层复合材料在800℃热震6次后只有暴露于表面的碳化钨颗粒发生了氧化,氧化深度小于30μm,裂纹扩展深度较小：(2)碳化钨颗粒在高温下被氧化为脆性氧化物WO3,氧化反应式为W2C+3O2-→2WO3+CO2,氧化起始温度为570℃,同时得出,随着温度的升高,抗氧化性呈降低趋势；(3)当温度低于570℃,复合材料热的热疲劳行为主要受热应力的影响,热冲击引起的循环交变应力使得热疲劳裂纹易于在宏观界面附近的增强颗粒与基体间的微观界面处萌生和扩展；(4)当温度高于570℃,氧化开始对复合材料的热疲劳行为产生影响,随着温度的升高影响逐渐增大。为了深入研究表层复合材料的热疲劳裂纹萌生和扩展机制,论文对表层复合材料的宏观界面、微观界面、复合层内的热应力进行了计算,结果表明：(1)建立了温度场与应力场相耦合的表层复合材料热应力计算模型：(2)通过该模型,获得：①在冷却过程中,宏观界面处的最大热应力为63.4MPa,远大于复合层其它位置的最大热应力(7.3MPa)：②微观界面处的最大热应力为38MPa,说明在热冲击作用下,交变循环应力最大为38MPa；③验证了表层复合材料的热疲劳裂纹易于在宏观界面附近的颗粒与基体间微观界面处萌生和扩展。更多还原

【Abstract】 With the development of modern industry, there is more components and parts applied in many industrial fields, such as metallurgy, mechanical, electricity and so on,with high temperature wear and sharp quenching. The ceramics particle reinforced surface composite have advantages not only in ductility but also toughness, modulus, hardness and so on. This composite can meet the wear-resistance requirements. It is a great candidate for replacing traditional metal materials in some wear working condition. However, there is thermal fatigue of quench heat shock in some complex wear working condition, it means that the surface composite must have thermal fatigue resistance. The cast tungsten carbide particle reinforced steel substrate surface composite was processed by vacuum suction casting infiltration method. The connection between microstructure of surface composite and thermal physical characters, mechanism of thermal fatigue crack initiation and propagation etc. was studied by microstructure analysis, thermal fatigue behavior investigation, thermal physical characters test, thermodynamics calculation and mechanical calculation.The connection between microstructure and thermal physical characters(thermal expansion coefficient, thermal capacity, thermal diffusion coefficient and thermal conductivity) of the surface composite was studied. The results showed:(1)The constitutes of the surface composite are WC、W2C、Fe2W2C、Fe3W3C、Cr7C3and martensite basically.(2)From the macroscopic interface between composite and substrate to surface of composite, the volume fraction of particle is increasing gradually, meanwhile, it is inversely proportion to thermal expansion coefficient, thermal capacity, thermal diffusion coefficient and thermal conductivity.(3)The thermal expansion coefficient, thermal capacity, thermal diffusion coefficient and thermal conductivity is inversely proportion to particle size of surface composite.(4) Below630℃, the thermal deformation stability of surface composite is great, and it is inversely proportion to particle size.The oxidizability and thermal fatigue behavior were studied by experimental observation and thermodynamic calculation.The results showed:(1)The oxidation and crack depth of surface composite is below30μm after6thermal shock cycles.(2)The particle is oxidated to WO3, the oxidation reaction is W2C+3O2→2WO3+CO2, the initial reaction temperature is570℃, the reaction rate is proportional to temperature.(3)Below570℃, the thermal fatigue behavior is influenced by thermal stress primarily, the thermal fatigue cracks are apt to initiate and propagate on the macroscopic interface.(4)Above570℃, the thermal fatigue behavior is influenced by oxidizability, the influence is enlarged with temperature increasement.The stress of macroscopic interface, microscopic interfaces and composite was calculated for studying the mechanism initiation and propagation thermal fatigue crack in deep. The results showed:(1)The thermal stress calculation model of surface composite is built.(2)the maximum stress of macroscopic interface is63.4MPa calculated by the model, it is much higher than the other areas of composite, the maximum stress of microscopic interface is38MPa.(3) The mechanism initiation and propagation of crack on macroscopic interface, the thermal fatigue cracks are apt to initiate and propagate on the macroscopic interface is testified by the calculation results.更多还原