A Study Of Fatigue Crack Growth Rate Of TC4-DT Titanium Lloy With Damage Tolerance

In order to meet the application background of some special fighters and the design requirement of high performance materials with damage tolerance, TC4-DT Ti alloy with self-intelligence property right was developed at NIN and BIAM, which is an α+β titanium alloy with damage tolerance and medium strength.As an important designing and indicating target of damage tolerance, the fatigue crack growth rate (FCGR) should be necessarily studied. Influence and action mechanism of sample direction, microstructure, stress ratio and sample dimension on the fatigue crack growth rate were systematically studied. Crack propagation mechanism of the alloy was investigated by means of microstructure observation, crack propagation path analyze, scanning electron micrograph fractography. The results indicated that:1. FCGR is sensitive to microstructure at lower AK region, the FCGR in T-L direction is apparently faster than that in L-T direction;and FCGR at T-L and L-T direction is tend to consistency with the increase of AK into Paris region, which is not insensitive to microstructure. FCGR is almost the same at L-T, T-L and 45 ° direction at Paris region, which indicating that the sample direction has little influence on FCGR.2. FCGR with fine lamellar weaven widmanstaten structure is the best, which is better than that with coarse lamellar plat widmanstaten structure. And FCGR with equiaxed or bi-modal microstructure is the worst.3. FCGR will decrease with thicker sample and smaller stress ratio at the same testing condition.4. Crack will propagate not only by circling but also by cutting pattern through primary a phase for the alloy with bimodal microstructure. Crack will propagate not only through colony boundary or parallel to a/p interface but also through cutting a and p phase with a certain angle (45 ° ,60° ,90° ) for the alloy with lamellar microstructure. Fracture mode in pre-crack region and fast-growth region is mainly micro-zone cleavage fracture, and in steady propagation region is mainly strip propagation mechanism, consisting with some cleavage fracture.5. Paris equation of FCGR for two-line segment by error and correlation coefficient analyze can be well described as follows:near I region: da/dN = 2.512 ×10^-12â–³K^6.41 (â–³K<â–³K₀)near III region: da/dN= 3.311 × 10^-8â–³K^2.99 (â–³K>â–³K₀)...