An Overview of Elevated Temperature Damage Mechanisms and Fatigue Behavior of a Unidirectional SCS-6/Ti-15-3 Composite

Abstract

Abstract The fatigue behavior of a unidireclionally reinforced titanium matrix composite (TMC), SiC/Ti-15-3, was thoroughly characterized to support life prediction modeling of advanced TMC disks designed for gas turbine engine rotor applications. The results of this coupon-level experimental investigation are reviewed in this paper. On a stress basis, the isothermal fatigue behavior of the [0°] TMC revealed significant improvements over the unreinforced matrix. In contrast, the [90°] TMC exhibited degraded properties and lives for similar comparisons. This was attributed to the weak fiber/matrix interfacial bond. Encasing the [0°] TMC with a Ti-15-3 case did not affect isothermal fatigue lives at higher strain levels. However, at lower strain levels, relatively rapid initiation and propagation of large fatigue cracks in the case degraded the fatigue lives. Thermomechanical fatigue (TMF) lives were significantly reduced for the [0°] TMC when compared to isothermal lives. At high strains, in-phase TMF produced extremely short lives. This degradation was attributed to fiber overload failures bought about by stress relaxation in the matrix. At low strains, out-of-phase TMF conditions became life-limiting. Environment-assisted surface cracking was found to accelerate fatigue failure. This produced extensive matrix damage with minimal fiber damage. For the [90°] TMC, TMF conditions did not promote an additional degradation in cyclic life beyond that observed under isothermal conditions.