Effects of Hydrogen on Fatigue Crack Propagation Rate of Ti-2Al-2.5Zr Titanium Alloy

The fatigue crack propagation rates of Ti-2Al-2.5Zr titanium alloy with three different hydrogen contents were measured at room temperature and the fracture surfaces were observed. Experiment reveals that behavior of the stable crack propagation conforms to the Paris Law, and hydrogen has little effects on da/dN in the stable crack propagation stage, but has marked effects on da/dN in the rapid fracture stage. Increasing hydrogen leads to decrease the stress intensity factor range delta ΔK at which the rapid rupture starts. Direction-preferable cracking of hydrides occurs in material with the highest hydrogen concentration at higher delta ΔK, so as to decrease the fracture toughness, which results in the smaller delta ΔK needed for the rapid rupture than the lower hydrogen materials.