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Elevated temperature low cycle fatigue behaviour of Haynes 282 and its correlation with microstructure - Effect of ageing conditions

机译：Haynes 282的高温低周疲劳行为及其与微结构的关系-时效条件的影响

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摘要

In this paper, total strain-controlled high temperature (760 degrees C) low cycle fatigue (HTLCF) behaviour (at 0.5% strain amplitude) of a new gamma'-strengthened wrought Ni based superalloy (Haynes 282) for various ageing conditions is presented for the first time, emphasizing the microstructural effects. Haynes 282 is a promising material for hot gas path components of ultra-supercritical steam turbines due to its adequate fatigue property at elevated temperatures, along with high creep and oxidation resistance. Various microstructures were generated by varying ageing time (1 day, 6 days and 9 days) and temperature (650 degrees C and 760 degrees C). While continuous cyclic hardening behaviour was witnessed for lower aging temperature (650 degrees C), predominantly cyclic softening after initial hardening through few cycles was observed for higher aging temperature (760 degrees C), due to formation of more number of larger size voids and secondary cracks in the later specimen during the testing (as characterized by X-ray tomography). Underlying deformation mechanisms (characterized through TEM) and fracture modes (characterized through SEM, EDS) were correlated to alloy's microstructures under various HTLCF conditions; distinct differences were observed between the two ageing temperatures. While 650 degrees C, 9 days ageing condition showed primarily signatures of gamma' shearing, 760 degrees C, 9 days ageing condition showed primarily the Orowan mechanism of deformation. For 650 degrees C ageing condition, predominantly intergranular fracture mode has been observed, which is attributed to the presence of brittle primary MC particles on the boundaries. Whereas for the 760 degrees C ageing condition, the fracture mode remained predominantly transgranular because it involves less crack deflection through its path. Plastic strain energy density based life prediction model were used to predict fatigue life. Close agreement between calculated and measured life indicates validity of these models for the present material.
机译：本文介绍了在各种时效条件下，新型γ'强化锻造镍基高温合金（Haynes 282）的总应变控制高温（760摄氏度）低循环疲劳（HTLCF）行为（应变振幅为0.5％）第一次强调微观结构效应。 Haynes 282具有超高的抗蠕变性和抗氧化性，是超超临界蒸汽轮机热气路径部件的有前途的材料，因为它在高温下具有足够的疲劳性能。通过改变时效时间（1天，6天和9天）和温度（650摄氏度和760摄氏度）来生成各种微结构。虽然观察到较低的时效温度（650摄氏度）具有连续的循环硬化行为，但对于较高的时效温度（760摄氏度），观察到初始硬化经过几个循环后主要是循环软化，这是由于形成了更多的较大尺寸的空隙和二次在测试过程中，后面的试样会出现裂纹（以X射线断层扫描为特征）。在各种HTLCF条件下，基本变形机制（通过TEM表征）和断裂模式（通过SEM，EDS表征）与合金的微观结构相关。在两个时效温度之间观察到明显的差异。在650摄氏度，9天的老化条件下，主要表现出gamma剪切的特征；而在760摄氏度，9天的老化条件下，则主要表现出Orowan变形机制。对于650℃的时效条件，主要观察到晶间断裂模式，这归因于边界上存在脆性的初级MC颗粒。而在760摄氏度的时效条件下，断裂模式仍主要是沿晶态的，因为它沿路径的裂纹变形较小。基于塑性应变能密度的寿命预测模型用于预测疲劳寿命。计算寿命和测量寿命之间的密切一致性表明了这些模型对于当前材料的有效性。

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