This work aims to evaluate the impact of a prolonged thermal aging on the fatigue crack growth properties of a commercial Ti 17 (Ti-5Al-2Sn-2Zr-4Mo-4Cr) titanium alloy. Aging was operated at 450 °C for extended times, of 1000 h and 10,000 h respectively. In terms of room-temperature tensile properties, aging is mainly responsible for a strain hardening of the material and a decrease in ductility, the total elongation dropping from 5.1% in the as-received state to 1.5% after 10,000 h. A significant increase in crack propagation rates at room temperature for R = 0.1 is observed, emphasizing an embrittling effect of aging. This last effect is however only noticed beyond a critical value of ΔK (ΔK_cr), which decreases with increasing aging times. It is observed that the effect of long-term aging on the mechanical properties is more pronounced during the early stage of the aging process, and tends to saturate for longer times. Tests with different load ratio of R = 0.4 and 0.7 were performed to gain a better understanding of the occurrence of these ΔK_cr values. The results indicate that the increase in propagation rates is actually governed by the static K_max component of the fatigue loading. Fractographical analysis of the failed specimens reveal that aging affects the material's resistance at a very fine scale, namely the α lamellae/β matrix interfaces. The detrimental role played by both grain boundary α phase and precipitate-free zones on the fatigue crack growth resistance of the material were finally discussed.

这项工作旨在评估长时间的热老化对商用Ti 17（Ti-5Al-2Sn-2Zr-4Mo-4Cr）钛合金的疲劳裂纹扩展性能的影响。老化在450°C下进行了1000小时和10,000小时的延长时间。就室温拉伸性能而言，时效主要是造成材料的应变硬化和延展性下降的原因，总伸长率从接受状态的5.1％降至10,000 h后的1.5％。对于R = 0.1，在室温下观察到裂纹扩展速率的显着增加，强调了时效的脆化效应。这最后的效果却是只注意到超出ΔK的临界值（ΔK _CR），随着老化时间的增加而减少。可以看出，长期时效对机械性能的影响在时效过程的早期阶段更为明显，并且趋于长时间饱和。进行与R = 0.4和0.7的不同负载比的测试，以便更好地这些ΔK的发生的理解_CR值。结果表明，传播速率的增加实际上是由静态K _{max决定的。}疲劳载荷的组成部分。断裂试样的分形分析表明，时效会在非常细小的范围内影响材料的电阻，即α薄片/β基质界面。最后讨论了晶界α相和无沉淀区对材料抗疲劳裂纹扩展的有害作用。