Fracture mechanisms of the SCS-6 fiber-reinforced titanium alloy matrix composites.

摘要

The mechanical properties and failure mechanisms of several SCS-6/Ti alloy matrix composites have been studied. Tensile, notched 3-point bending, low cycle fatigue and fatigue crack propagation test were conducted at room temperature on the unidirectional SiC fiber-reinforced Ti-15V-3Cr-3Al-3Sn, Ti-6Al-4V and Ti-25Al-10Nb-3V-1Mo composites. Microstructural parameters controlling the deformation, damage initiation and growth of the composites were investigated using metallographic technique and fractographic analysis. These parameters include interfacial reaction between fiber and matrix, interfacial mechanical properties, matrix toughness, fiber strength and loading conditions.; The resulting deformation and fracture mechanisms of these composites under quasi-static and notched 3-point bend loading were classified on the basis of the ratio of the fiber strength ({dollar}sigmasb{lcub}rm f{rcub}{dollar}) to interfacial shear strength ({dollar}tausb{lcub}rm i{rcub}{dollar}) vs. matrix toughness. These failure mechanisms will provide a scientific basis for the development of an analytical model to predict the micro- and macro-fracture processes of fiber-reinforced metal matrix composites. Furthermore, the low cycle fatigue damage diagram was constructed using the maximum stress in the fiber vs. fatigue life. Depending on the stress levels applied, the fatigue damage of the composites can be classified into three regions: (1) fiber breakage dominated, (2) interfacial cracking, matrix cracking and fiber breakage dominated (progressive) and (3) matrix cracking dominated. Matrix cracking with bridging fibers in the wake of the crack tip was the major mechanism for the fatigue crack propagation behavior of the composites. The transition from the noncatastrophic to catastrophic mode I failure was controlled by the fiber breakage in the wake of crack. A micromechanical model was also proposed to predict the fatigue crack propagation behavior of the composites. These results will be used as guidelines for the selection of processing parameters, fiber coating, and matrix modification, in order to develop high-performance metal matrix composites.