Microplasticity and tensile damage in Ti-15V-3Cr-3Al-3Sn alloy and Ti-15V-3Cr-3Al-3Sn/SiC composite

Microscopic evidence of plastic flow at stresses below the bulk yield stress is presented for a metastable beta titanium alloy (Ti-15V-3Cr-3Al-3Sn) and model Ti-15V-3Cr-3Al-3Sn/SiC composite deformed to failure under monotonic loading at room-temperature. Microplasticity is shown to initiate in Ti-15V-3Cr-3Al-3Sn (Ti-15-3) alloy at stress levels between 5 and 10% of the bulk yield stress. Evidence of microplasticity is obtained via scanning electron microscopy examination of the deformed surfaces of smooth specimens that are loaded in incremental stages to failure. In the case of the monolithic Ti-15-3 alloy, deformation is shown to occur by a wide range of mechanisms at room temperature. These include: grain boundary sliding, grain boundary flow and bulk flow mechanisms. A wider range of matrix damage is observed in the model Ti-15-3/SiC composite deformed to failure under monotonic loading. These include all the damage components observed in the matrix and additional damage shear localization/slip band formation which is presumed to occur as a result of constraint effects in the composite. Plasticity in the Ti-15-3/SiC composite is also shown to involve early interfacial debonding, fiber fracture and multiple crack coalescence stages prior to the onset of catastrophic failure. The potential implications of the above results are also discussed.