Cracking behaviours and stresses release in titanium matrix composites

The present study focuses on the utilisation of acoustic emission (AE) as w ell as scanning electron microscopy (SEM) for the identification and charac terisation of stresses release and failure modes of continuous SiC-fibre re inforced titanium matrix composites (TMCs) after various thermomechanical c yclings 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 1.5 x 3.0 x 100 mm. A range of thresholds from 26 to 50 d B and a range of filter frequencies from 200 to 1200 kHz for AE measurement s were set up. AE amplitudes in the matrix are relatively low because of th e ductile property of matrix sources. Acoustic emission originates primaril y from the fibres and their interfaces with the matrix. Different behaviour s were found for the SiC-TMC specimens during tensile loading and thermomec hanical cycling. AE history records and amplitude distributions, coupled wi th the stress-strain curves and SEM observations indicate that the fracture mechanisms of SiC-TMC materials consist of debonding, fibre pull out, fibr e breakage and matrix cracking. (C) 2000 Elsevier Science S.A. All rights r eserved.