Cracking behaviours and stresses release in titanium matrix composites

The present study focuses on the utilisation of acoustic emission (AE) and scanning electron microscopy (SEM) for the identification and characterisation of stresses release and failure modes of continuous SiC-fiber reinforced titanium matrix composites (TMCs) after various thermomechanical cyclings under different experimental conditions. Ti-6Al-4V/SiC (SCS-6, 35% vol., 140 mu m in diameter) was investigated in this work. The dimension of the specimen was 1.5x3.0x100 mm. A range of thresholds from 26-50 dB and a range of filter frequencies from 200-1200 kHz or AE measurments were set up. Acoustic emission amplitudes in the matrix are relatively low because of the ductile property of matrix sources. Acoustic emission originates primarily from the fibers and their interfaces with the matrix. Different behaviors were found for the SiC-TMC specimens during tensile loading and thermomechanical cycling. Acoustic emission history records and amplitude distributions, coupled with the stress-strain curves and SEM observations indicate that the fracture mechanisms of SiC-TMNC materials contist of debonding, fiber pull out, fiber breakage and matrix cracking.