Study on the Fatigue Crack Growth of TC17 Titanium Alloy with Three Mcrostructures

Abstract:

Three typical microstructures for TC17 titanium alloy, i.e. equiaxed microstructure, basket-waved microstructure and globularized microstructure, are obtained by conventional forging, beta forging and “beta pre-forging+subtransus forging”, and Fatigue crack growth rates of TC17 samples with the three microstructures are tested in order to evaluate the influence of different microstructures. The results reveal a significant dependence of microstructure on fatigue crack growth rate for this material. Basket-waved microstructure has an excellent fatigue crack growth resistance, followed by globularized microstructure, while the equiaxed microstructure shows the poorest propagation resistance. On the basis of fracture mechanics, prediction models for fatigue crack growth life based on Paris equation are developed respectively for the three different microstructures. The models suggest that the propagation life for the large crack in the three microstructure accounts for only a very small proportion of the total fatigue life, hence the control of crack initiation is more important. Superior propagation resistance means a longer critical crack length, which is easily testable in practice.

Key words:TC17 titanium alloy; fatigue crack growth; equiaxed microstructure; basket-waved microstructure; globularized microstructure