Improvement of fatigue properties of Ti-6Al-4V alloy under four-point bending by low temperature nitriding

Low temperature nitriding (LTN) was performed for titanium alloy (Ti-6Al-4V) to improve its fatigue properties. A nitrogen compound layer was formed on the surface nitrided at temperatures higher than 873 K, whereas nitrogen diffusion was observed on the surface nitrided at 823 K. Fatigue tests were performed by four-point bending in air under a stress ratio of 0.1. The fatigue limit for Ti-6Al-4V tended to increase with a decrease in the nitriding temperature. LTN at 823 K increased the fatigue limit of Ti-6Al-4V due to the formation of the surface with no nitrogen compound layer and suppression of grain-coarsening.