Fatigue crack growth behaviour of Ti-6 Al-4V metal matrix/continuous SiC and B4C/B fibre composites

The effect on fatigue crack growth (FCG) of modifying the interface between fiber and matrix in SiC and B4C/B-reinforced Ti-6Al-4V metal matrix composites by isothermal and thermal cycle treatments has been studied. The thermal cycling and isothermal treatments were carried out in air, sulfur, and vacuum. The results demonstrated that the interface transferred the load during fatigue cycling in inert environment or when the interface had a minimal amount of impurities. For a sulfur-enriched interface, the humid-air FCG environment reduced the cohesion of the interface, resulting in the applied load being carried solely by the matrix. This led to an increased FCG rate with a higher value of the Paris exponent. Without enhanced sulfur at the interface, the Paris exponent remained constant, although the FCG rate nominally increased in a humid air environment.