| The damage tolerance behavior of two kinds of new titanium alloys, TC4-DT and TC21, were studied and evaluated in this paper by using macroscopic experimental and microcosmic analysis methods. The studies were focused on tensile strength, fracture toughness, fatigue crack growth rate and threshold value, HCF properties, and the behavior and life estimation of fatigue crack growth under random spectrum load. The main results from the present study can be summarized as bellow:(1) TC4-DT, a moderate strength titanium alloy, has good ductility, and TC21, a high strength titanium alloy, has inferior ductility . The overall properties of TC21 alloy with basketweave microstructure are better than that of the lamellar micro structure.(2) Fracture toughness of TC4-DT alloy is obviously higher than that of TC4 alloy. The apparent fracture toughness Kapp of TC4 alloy is strongly influenced by the sample thickness but this is not the case for TC4-DT alloy. The lamellar microstructure of TC4-DT alloy can effectively improve the fracture toughness, but the bimodal microstructure of TC4 alloy is beneficial to ductility improvement. Compared with the TC17 alloy, TC21 alloy has superior damage tolerance properties.(3) TC4-DT alloy presents good ductility and high fracture toughness properties, and TC21 alloy has the higher tensile strength and higher fracture toughness. The damage tolerance properties of TC21 alloy are not as good as those of the TC4-DT alloy.(4) The HCF property of TC21 with baskerweave microstructure is better than TC4-DT with lamellar microstructure. Fatigue crack in TC21 alloy mostly initiate from a single position. In contrast, multiple cracks are commonly found in TC4-DT alloy.(5) The estimated fatigue crack growth life using Willenberg model withαβcorrection factor agreed well with experimental results, and the results from the Willenberg+IZ model were in good agreement with experimental data for TC4-DT alloy. |
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