An investigation of the effects of interfacial microstructure on the fatigue behavior of a four-ply [75]₄ continuous silicon carbide (SCS-6) fiber-reinforced titanium matrix composite

The effects of interfacial microstructure/thickness on the strength and fatigue behavior of a model four-ply [75]4 Ti-15V-3Al-3Cr-3Sn/SiC (SCS-6) composite are examined in this article. Interfacial microstructure was controlled by annealing at 815 °C for 10, 50, or 100 hours. The reaction layer and coating thickness were observed to increase with increasing annealing duration. Damage initiation/propagation mechanisms were examined in as-received material and composites annealed at 815 °C for 10 and 100 hours. Fatigue behavior was observed to be dependent upon the stress amplitude. At high stress amplitudes, the failure was dominated by overload phenomena. However, at all stress levels, fatigue crack initiation occurred by early debonding and matrix deformation by stress-induced precipitation. This was followed by matrix crack growth and fiber fracture prior to the onset of catastrophic failure. Matrix shear failure modes were also observed on the fracture surfaces in addition to fatigue striations in the matrix. Correlations were also established between the observed damage modes and acoustic emission signals that were detected under monotonie and cyclic loading conditions.