Experimental Investigation of High-temperature Crack Propagation Behaviors for Ti-6Al-4V/ELI at 250 <b>℃</b>

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Experimental Investigation of High-temperature Crack Propagation Behaviors for Ti-6Al-4V/ELI at 250 ℃

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LYU Zhiyang / XIONG Junjiang / ZHAO Yanguang / MA Shaojun

Fatigue crack propagation behaviors at high temperature are important preconditions for damage tolerance design in aircraft and engine structures.Therefore, fatigue tests were carried out on titanium alloy Ti-6Al-4V/ELI subjected to constant amplitude loading at two temperatures of 25 ℃ and 250 ℃ and three stress radios of 0.06, 0.5, -1 to determine fatigue crack propagation behaviors. Fatigue crack propagation da/dN-ΔK curves and da/dN-ΔK-R surfaces were obtained from experimental data by secant method. Those behaviors at different temperatures were compared and analyzed, and the interaction mechanism between high-temperature and fatigue load was deduced from fractographical study by SEM analysis.The results show that the larger the stress ratio R, the faster the rate of crack propagation of Ti-6Al-4V/ELI under the same temperature and stress intensity factors rangeΔK. Oxidation products and large numbers of secondary cracks are found on the fatigue fracture surfaces at high temperature and the destruction mode of crack propagation is gradually changed form cleavage to quasi-cleavage. Acceleration effect of oxidation and deceleration effect of secondary cracks combine affecting the crack propagation rate; when R is 0.5 or 0.06, those two seem equal and the effect of temperature is not obvious, while R is -1, more and deeper secondary cracks caused by fully interaction of high temperature and fatigue load make crack propagation rate at high temperature lower than that at room temperature.