Effect of prolonged high-temperature exposure on the fatigue and fracture behavior of aluminum-lithium alloy 2090

K.T Venkateswara Rao, R.O Ritchie
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引用次数: 23

Abstract

Effects of prolonged exposures of 100–1000 h at 163°C on fatigue crack propagation and fracture toughness behavior have been studied in commercial aluminum-lithium alloy 2090-T8E41, and results compared with behavior in similarly over-aged 2124 alloy. Over-aging in 2090, which led to decreases in strength and toughness principally through the formation of plate-like copper-rich grain boundary precipitates and associated copper-depleted and δ′ precipitate-free zones, was found to result in increased fatigue crack growth rates above ∼ 10−9 m cycle−1; near-threshold growth rates were less affected. Such behavior is related to a diminished role of crack-tip shielding during crack extension in over-aged microstructures, from less crack deflection and lower crack closure levels (from asperity wedging), arising from more linear crack paths. Despite this degradation in fatigue crack growth properties following high temperature exposure, crack growth rates in the over-aged 2090 remain comparable or superior to traditional high strength aluminum alloys, such as 2124-T351 and 7150-T651, due primarily to higher overall levels of crack-tip shielding.

长时间高温暴露对2090铝锂合金疲劳断裂行为的影响
研究了在163℃下长时间暴露100-1000 h对2090-T8E41铝锂合金疲劳裂纹扩展和断裂韧性行为的影响,并将结果与同样超长时效的2124合金进行了比较。2090年的过度时效导致强度和韧性下降,主要是通过形成板状富铜晶界析出物和相关的贫铜和无δ′析出物区,导致疲劳裂纹扩展速率在~ 10 ~ 9 m循环−1以上增加;接近临界值的增长率受到的影响较小。这种行为与在过时效微结构中裂纹扩展过程中裂纹尖端屏蔽作用的减弱有关,这是由于更线性的裂纹路径引起的更少的裂纹偏转和更低的裂纹闭合水平(由粗糙楔入)。尽管高温暴露会导致疲劳裂纹扩展性能下降,但2090超龄合金的裂纹扩展速率仍然与传统的高强度铝合金(如2124-T351和7150-T651)相当或优于后者,这主要是由于裂纹尖端的整体屏蔽水平更高。
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