High cycle fatigue behavior of the in-situ TiB2/7050 composite

The microstructure and high cycle fatigue behavior of the in-situ TiB2/7050 composite were investigated in this work. The results showed that with the addition of sub-micron size TiB2 particles, the in-situ TiB2/7050 composite exhibited the smaller grain size, higher elastic modulus, enhanced yield strength and ultimate tensile strength, and superior fatigue limit over the unreinforced 7050 alloy. Through the fatigue tests, most of the fatigue cracks initiated at inclusions near the surface of both the composite and unreinforced alloy testing samples. The fatigue cracks initiation was induced by the stress concentration that was caused by the pileup of dislocations. In consideration of the improved fatigue properties of composites, the finer grains and higher elastic modulus in the composite were benefited to such enhancement. Critically, a new viewpoint was proposed that the submicron TiB2 particles impeded dislocations from piling up at the inclusions and delayed the crack initiation there, which can improve the fatigue property efficiently in the composite.