Research On The Damage Tolence Of TC21Titanium Alloy

TC21 titanium alloy is a new kind ofα+βtwo-phase titanium alloy with great application prospect in the manufacture of aeronautic and astronautic structural parts. The damage tolerance behaviour of TC21 titanium alloy must be researched in order to meet the demand of damage tolerance design rules. Fracture toughness, crack growth rate and crack growth threshold are three important indexes characterizing damage tolerance, and especially the influence of microsturecure on damage tolerance is worth of deeply researching. Based on the above reason, this paper conducted the research of models of fracture toughness, crack growth rate and crack growth threshold of TC21 titanium alloy. The main contents are as follows:Firstly, according to the theory of fracture mechanics, the relationship between four Fracture Criteria was integrated under linear elasticity. The characteristic parameters of basketweave microstructure attended under different heat treatments were measured through quantitative metallography technique. On the basis of analyzing the influence of microstructure on the fracture toughness of TC21 titanium alloy, the mathematical model that the fracture toughness depended on the width ofαphase, the width ofαbundle and material constants was constructed. The model will provide valuable theory basis and design reference for the research of new kind titanium alloy and industrial application.Secondly, in order to develop damage tolerance design on components of TC21 titanium alloy and estimate its fatigue lifetime, the main basis is fatigue life formula, which can be derived from the integration of the fatigue crack growth rate. Thereby, it is the key to choose a proper fatigue crack growth rate formula to develop damage tolerance design on components. According to the fatigue crack growth data of TC21 titanium alloy, the model which can describe the three stages of fatigue crack growth was chosen and the parameters of the model were fitted using least square method and regression analysis. The model will provide reference for damage tolerance of TC21 titanium alloy components.Lastly, the crack growth threshold is another important index of damage tolerance design. The kinds of crack closure mechanisms due to crack deflection and branching, plastic wake, fracture-surface asperity and roughness, as well as oxide wedging were important factors influencing fagitue crack growth threshold value. Researching and analyzing quantificationally the influence of above factors on fagiture crack growth threshold have important theory value and engineer significance.