Out-of-phase thermomechanical fatigue of titanium composite matrices

A study was undertaken to evaluate the out-of-phase thermomechanical fatigue behavior of three titanium-based alloys: Ti-15Mo-2.6Nb-3Al-0.2Si, Ti-14Al-21Nb, and Ti-13Al-31Nb. The alloys represent compositions from three classes of Ti alloys which have been considered as matrices for titanium-matrix composites. Several tests of each alloy were performed at various maximum stresses, all with a stress ratio of 0.05, a 3 min cycle period, and a temperature cycle of 150 °C to 650 °C. The fatigue lives are compared evaluating S-N behavior and fracture characteristics. In general, the behavior of the Ti-15Mo-2.6Nb-0.2Si alloy was governed by higher toughness compared to the other two alloys, and the Ti-13Al-31Nb alloy demonstrated improved performance over the Ti-14Al-21Nb alloy. A correlation with existing composite data was noted. The correlation is based on calculated micromechanical stresses in the matrix of the composites and applied stresses on the monolithic materials.