Effects of three stress levels on the fatigue properties and fracture mechanisms of an in-situ synthesized TiB/Ti-6Al-4V titanium matrix composite

Due to reinforcements, titanium matrix composites (TMCs) exhibit different fatigue properties and more complex fatigue failure mechanism than titanium alloys. In order to systematically investigate the fatigue failure mechanism of TMCs, 8% TiB/Ti-6Al-4V was selected and the high-frequency cyclic fatigue tension-compression tests under different stresses were conducted. The fatigue life of specimens under different stresses were obtained and analyzed. The microstructure of fracture morphology and the cross-sections were characterized and discussed as well. The results showed that the fatigue life of 8% TiB/Ti-6Al-4V decreased with increasing the loading stress. The fracture morphology of 8% TiB/Ti-6Al-4V indicated that the “cleavage facets” were obviously observed in the crack initiation region. In addition, the existence of “small planes” with different areas was shown in the crack propagation region while changing the loading stress. With the change of loading stress, the fracture mode of TiB also changed from interface separation to debonding, and finally completely pulled out, leaving a clear and visible trace on the fatigue section. By observing the propagation path of the main crack, it was found that the deflection angle of the main crack would also change greatly under different loading stresses. In addition, many microcracks and micropores sprouting at the tip of TiB were found. This work provides a theoretical and experimental reference for improving the fatigue properties of TMCs.