Cracking behaviours and stresses release in titanium matrix composites

The present study focuses on the utilisation of acoustic emission (AE) as well as scanning electron microscopy (SEM) for the identification and characterisation of stresses release and failure modes of continuous SiC-fibre reinforced titanium matrix composites (TMCs) after various thermomechanical cyclings under different experimental conditions. Ti–6Al–4V/SiC (SCS-6, 35% vol., 140 μm in diameter) was investigated in this work. The dimension of the specimen was 1.5×3.0×100 mm. A range of thresholds from 26 to 50 dB and a range of filter frequencies from 200 to 1200 kHz for AE measurements were set up. AE amplitudes in the matrix are relatively low because of the ductile property of matrix sources. Acoustic emission originates primarily from the fibres and their interfaces with the matrix. Different behaviours were found for the SiC-TMC specimens during tensile loading and thermomechanical cycling. AE history records and amplitude distributions, coupled with the stress-strain curves and SEM observations indicate that the fracture mechanisms of SiC-TMC materials consist of debonding, fibre pull out, fibre breakage and matrix cracking.