激冷激热环境下陶瓷颗粒增强表层复合材料的热疲劳裂纹形成机制研究

Under sharp quenching working condition, the formation of thermal fatigue crack is significant for the service life of the ceramic particle reinforced steel or iron substrate surface composite. And thermal stress in the composite is the key factor that induce the thermal fatigue crack. In this project, tungsten carbide particle reinforced steel substrate surface composite is chosen as the research subject. Firstly, the composites are fabricated by the spark plasma sintering and vacuum interface remelting method which can controll the microstructure. Secondly, the thermology and mechanical properties of the brittle phases, which include tungsten carbide particle, carbides in the composite and so on, are investgated by first-principle calculation, microstructure investigation, properties test methods etc.. The thermal stress in the brittle phases and between the brittle phases and matrices are described by mathematical model. Therefore, the criteria for the probability of the thermal fatigue crack formation in the composites is obtained. At last, combined with the judgment and the thermal fatigue behavior under sharp quenching working condition, the formation mechanism of the thermal fatigue crack is explored.The results of this project could greatly extend the application area of tungsten carbide particle reinforced steel or iron substrate composite and other materials containing the similar microstructure. And it would offer the theoretical basis for achieving the successful application of the composites under the sharp quenching working condition.

激冷激热环境下热疲劳裂纹形成是陶瓷颗粒增强钢（铁）基表层复合材料寿命下降的重要原因，而复合材料中的热应力作用又是诱发其热疲劳裂纹形成的关键因素。项目以碳化钨颗粒增强钢基表层复合材料为研究体系，首先采用等离子快速烧结 (SPS) + 真空界面重熔的研究方法模拟材料制备，实现组织可控；然后利用第一原理计算、微观结构表征及性能测试等方法，研究表层复合材料中碳化钨颗粒、碳化物等脆性相的热学、力学性质，建立碳化钨颗粒增强钢基表层复合材料中脆性相及其与基体间界面处的热应力作用模型，获得其热疲劳裂纹的形成倾向判据；最后结合表层复合材料的热疲劳行为研究，探索其在激冷激热环境下的热疲劳裂纹形成机制。项目的实施将大大拓展陶瓷颗粒增强钢（铁）基表层复合材料及其他具有类似组织结构材料的应用领域，并为其在激冷激热工况下的成功应用奠定理论基础。

项目以矿山、冶金用耐磨复合材料为应用背景，以碳化钨颗粒增强钢基复合材料为研究对象，重点开展了激冷激热工况下复合材料的热疲劳裂纹形成及其与热疲劳行为间的关联机制研究。首先，采用等离子快速烧结(SPS) + 真空界面重熔方法，对工艺参数进行优化，成功制备了界面可控的碳化钨颗粒增强钢基表层复合材料；其次，结合第一性原理、热力学计算及SEM、XRD等分析测试手段，获得了碳化钨颗粒与基体间的界面反应机制和反应产物M6C型碳化物的反应机理；然后，对复合材料中不同组元的热学（热膨胀系数、热扩散系数、比热等）、力学性能（弹性模量、硬度等）参数进行测试和计算，探索了复合材料在激冷激热环境下的热疲劳裂纹形成机制，建立了复合层与基材间的宏观界面、颗粒与基体间的微观界面热应力数学模型 ，宏观界面处的最大热应力为63.4 MPa，远大于复合层其它位置的最大热应力（7.3 MPa），微观界面处的最大热应力为38 MPa，获得了宏观界面处陶瓷颗粒界面反应区为热疲劳环境中的薄弱环节等结论。最后，利用热震、SEM等分析测试手段，深入观察不同复合材料的热疲劳行为，结合表层复合材料的热应力作用机制研究的结果，探索了表层复合材料的热疲劳裂纹形成倾向，获得了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等结论，验证了界面热应力数学模型。项目的开展，为陶瓷颗粒增强钢（铁）基表层复合材料的结构优化设计提供了支持，为提高该类复合材料在激冷激热工况下的安全服役并扩大其应用范围奠定了坚实的理论基础。