变温时效对镍基高温合金组织的影响

Influence of Variable Temperature Aging on the Microstructure of Nickel-Based Superalloys

摘要:

镍基合金实际服役过程中面临着复杂的温度变化，温度波动可能改变元素的扩散路径和速率，从而影响组织的均匀性。现有的长期时效试验大多采用等温条件，变温时效过程中的组织演变和性能损伤研究鲜有报道。本研究旨在探究镍基合金等温时效与变温时效组织演变的差异以及变温次序对组织的影响；并建立组织与时间、温度之间的关系以及计算等效时间。结果表明， DZ411合金变温与等温时效γ′相尺寸增长与时间-温度之间具有相同的函数关系，即尺寸的立方差与时间、温度具有线性关系，两者的形状因子（Feret ratio, FR）也在相近范围内波动。同时，温度次序对γ′相尺寸具有规律性影响，组织观察表明，900 ℃-980 ℃次序γ′相尺寸均高于980 ℃-900 ℃次序；定量分析可知，900 ℃-980 ℃次序γ′相等效直径的平均值为719 nm，高于980 ℃-900 ℃次序的665 nm。此外，温度次序对γ′相形状同样具有规律性影响，组织观察表明，900 ℃-980 ℃次序与980 ℃-900 ℃次序γ′相颗粒分别以圆角矩形状与球状为主；定量分析可知，900 ℃-980 ℃次序FR平均值为1.411，高于980 ℃-900 ℃次序的1.379。

Abstract:

Nickel-based alloys undergo complex temperature variations during actual service. Thermal fluctuations may alter elemental diffusion pathways and rates, thereby affecting microstructural homogeneity. Current long-term aging studies predominantly focus on isothermal conditions, while microstructural evolution and performance degradation under non-isothermal aging remain inadequately explored. This study aims to investigate the differences in γ′ phase evolution between isothermal and non-isothermal aging in nickel-based alloys, elucidate the influence of variable temperature sequences on microstructural characteristics, and establish quantitative relationships among microstructure, aging time, and temperature, including equivalent time calculations. The results reveal that the growth kinetics of γ′ phase size in DZ411 alloy under both non-isothermal and isothermal aging follows an identical time-temperature function: the cube of phase diameter exhibits a linear dependence on aging time and temperature, with Feret ratio (FR) fluctuating within comparable ranges. Furthermore, variable temperature sequences systematically govern γ′ phase dimensions. Microstructural observations demonstrate that sequential aging from 900 ℃ to 980 ℃ produces larger γ′ phases than the reverse sequence (980 ℃-900 ℃). Quantitative analysis confirms that the average equivalent diameter (D) for the 900 ℃-980 ℃ sequence is 719 nm, which is larger than that for the 980 ℃-900 ℃ sequence (665 nm). Additionally, variable temperature sequences regulate γ′ phase morphology: rounded rectangular particles dominate in the 900 ℃-980 ℃ sequence, while near-spherical shapes prevail in the 980 ℃-900 ℃ sequence, supported by distinct FR values (1.411 vs. 1.379).