Microstructure evolution and mechanical properties of Inconel 740H during aging at 750 掳C

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• 作者：Chong Yan ; Liu Zhengdong ; Andy Godfrey ; Liu Wei ; Weng Yuqing
• 关键词：Inconel 740H ; Microstructure evolution ; 纬&prime ; precipitates ; Mechanical properties ; Three-dimensional atom probe
• 刊名：Materials Science and Engineering: A
• 出版年：1 January, 2014
• 年：2014
• 卷：589
• 期：Complete
• 页码：153-164
• 全文大小：6732 K

文摘

The microstructure evolution of Inconel 740H during aging at 750 掳C for up to 3000 h was investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), three-dimensional atom probe (3DAP) analysis and micro-phase analysis. The mechanical properties of samples after aging were also studied. The grain size increased substantially during the whole aging period. Two different types of grain boundary carbides were observed; block-shaped and needle-shaped. Both were identified to be M₂₃C₆ by selected area diffraction measurements. The grain boundary carbides did not coarsen significantly during aging, with the weight fraction increasing only from 0.20% to 0.28%. In contrast, a much higher coarsening rate of 纬鈥?precipitates was observed, as evidenced from both TEM observations and SAXS analysis. 3DAP was used to study the elemental partitioning behavior between 纬鈥?precipitates and 纬 matrix as well as the evolution in width of the 纬/纬鈥?interface. A large increase in the width of 纬/纬鈥?interfaces was seen between 1000 h and 3000 h aging. In addition, for the sample aged at 750 掳C for 3000 h, Cr enrichment on the 纬 matrix side of the 纬/纬鈥?interface was found. Tensile tests at 750 掳C of the aged samples showed a gradual decrease in elevated-temperature yield strength after 500 h, when this alloy was over-aged. The critical precipitate size for the transition from precipitate cutting by weakly coupled dislocations to strongly coupled dislocations for Inconel 740H was calculated to be approximately 50 nm, which agrees well with the experiment measurements of elevated-temperature yield strength. The room temperature impact toughness of all samples decreased during aging as the grain size kept growing.