Mechanism of Degradation of Mechanical Properties of Metal Matrix Composite due to Interfacial Reaction

为了描述界面反应和涂层处理对金属复合材料力学性能的影响，从实验和理论上研究了反应层对氧化铝纤维增强铝基复合材料室温强度和高温强度的影响，以及涂层(或反应层)与纤维之间的力学相互作用。这种化合物在变形的早期阶段断裂，在纤维表面形成裂纹，降低了纤维的强度。通过计算纤维在裂纹尖端的能量释放率，定量地描述了这一现象。另一方面，在高温下，化合物表现为塑性，从而降低了能量释放速率，导致纤维的高强度。在很高的温度下，基体的软化导致复合材料的强度因临界长度的增加而降低。(B)提出了一种新的计算方法来描述有涂层的纤维的强度。用该方法较好地描述了涂层与纤维弹性性能的差异对纤维强度的影响。该方法对涂层处理的设计具有一定的参考价值。该方法的应用表明，高模型炭纤维的临界能量释放率为3J/m^2，高强型碳纤维的临界能量释放率为2J/m^2，这在该领域尚属首次。

In order to describe the degradation due to interfacial reaction and coating treatment in mechanical properties of metallic composites, the influence of reaction layer on room and high temperature strength of alumina fiber-reinforced aluminium composite, and mechanical interaction between coating(or reaction)layer and fiber were studied experimentally and theoretically.(A)In alumina/aluminium composite, a metallic compound CuAl_2 was formed by addition of copper element into matrix. This compound fractured in an early stage of deformation, forming crack on fiber surface, which reduced fiber strength. This phenomenon was described in a quantitative manner by calculation of energy release rate of fiber at crack-tip. On the other hand, at high temperatures, the compound behaved plastically, which decreased energy release rate, resulting in high strength of fiber. At very high temperatures, the softening of matrik caused reduction in strength of composite due to increase in critical length.(B)A new calculation method was proposed to describe the strength of fiber with coating layer. With this method, the influence of difference in elastic properties between coating layer and fiber on strength of fiber was well described. This method is useful to design the-coating treatment. The application of this method revealed that the high modulus-type carbon fiber has critical energy release rate of 3 J/m^2 and the high strength-type one 2 J/m^2 This is the first finding in this field.