2024-T3铝合金高温低周疲劳失效机理研究

Investigation of the elevated-temperature low-cycle fatigue failure mechanism of 2024-T3 aluminum alloy

摘要:

为明确轻量化铝合金钻杆材料在深部钻探高温交变载荷下的疲劳失效行为，以2024?T3铝合金为研究对象，开展了120、160、200 ℃温度下，应力幅分别为200、250、300 MPa条件下的轴向拉?压应力控制疲劳试验，并结合应力?应变滞回响应、扫描电镜断口形貌及背散射电子成像对其失效机制进行了分析。结果表明，疲劳寿命随应力幅升高显著降低，应力幅是控制寿命衰减的主要因素；温度对寿命的影响具有明显的应力幅相关性；在200、250 MPa中低应力幅下，200 ℃试样寿命较160 ℃有所回升，而在300 MPa高应力幅下寿命随温度升高持续降低。滞回环分析表明，160 ℃条件下材料循环塑性变形增强，宏观非弹性能量耗散增加；200 ℃条件下滞回环面积并未随温度升高持续增大，表明宏观耗散能与局部疲劳损伤之间并非完全对应，疲劳失效逐渐由均匀塑性耗散主导向局部应变集中及颗粒?基体界面损伤主导转变。断口观察表明，低温低应力幅下裂纹以较稳定的疲劳辉纹扩展为主；随着温度和应力幅升高，断口粗糙化加剧，二次裂纹、韧窝、撕裂棱及颗粒拔出特征增多。BSE结果显示，Cu富集粗大第二相颗粒及其局部聚集区是裂纹萌生和扩展的重要微观损伤源。综合分析认为，2024?T3铝合金高温疲劳失效受基体热软化、循环塑性变形和颗粒?基体界面损伤共同控制，高温高应力幅下界面脱黏与微孔聚合加速了裂纹扩展并导致疲劳寿命降低，研究成果可为特深井轻量化铝合金钻杆的服役可靠性评价提供试验支撑与理论依据。

Abstract:

To elucidate the elevated-temperature fatigue failure behavior of lightweight aluminum alloy drill pipe materials in deep drilling， axial tension-compression stress-controlled fatigue tests were conducted on 2024-T3 aluminum alloy at 120， 160， and 200 °C with stress amplitudes of 200， 250， and 300 MPa. The failure mechanisms were analyzed via stress-strain hysteretic response， scanning electron microscopy fracture morphology， and backscattered electron imaging. The results show that fatigue life decreases markedly with increasing stress amplitude， which is the primary factor controlling life attenuation. The influence of temperature exhibits significant stress amplitude dependence； at intermediate and low stress amplitudes of 200 and 250 MPa， the fatigue life at 200 °C shows a recovery compared with that at 160 °C， whereas at a high stress amplitude of 300 MPa， it declines continuously with rising temperature. Analysis of the hysteretic response reveals that cyclic plastic deformation is enhanced at 160 °C， resulting in increased macroscopic inelastic energy dissipation. However， at 200 °C， the hysteresis loop area does not expand continuously， indicating a discrepancy between macroscopic dissipated energy and local fatigue damage， with the dominant failure mechanism shifting from uniform plastic dissipation to localized strain concentration and particle-matrix interface damage. Observations of fracture morphology indicate that crack propagation is dominated by stable fatigue striations at low temperatures and low stress amplitudes. Elevated temperatures and high stress amplitudes lead to rougher fracture surfaces with increased secondary cracks， dimples， tear ridges， and particle pull-out features. Backscattered electron imaging confirms that Cu-enriched coarse second-phase particles serve as critical microscopic damage sources for crack initiation and propagation. It is concluded that the fatigue failure is jointly governed by matrix thermal softening， cyclic plastic deformation， and particle-matrix interface damage. Under high-temperature and high-stress-amplitude conditions， interface decohesion and microvoid coalescence accelerate crack propagation and reduce fatigue life. The findings provide experimental support and a theoretical basis for service reliability evaluation of lightweight aluminum alloy drill pipe in ultra-deep wells.