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金属学报  2017, Vol. 53 Issue (12): 1627-1635    DOI: 10.11900/0412.1961.2017.00218
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Inconel 740H合金原位高温拉伸微裂纹萌生扩展研究
王晋1, 张跃飞1(), 马晋遥1, 李吉学2, 张泽2
1 北京工业大学固体微结构与性能研究所 北京 100124
2 浙江大学材料科学与工程系 杭州 310058
Microcrack Nucleation and Propagation Investigation ofInconel 740H Alloy Under In SituHigh Temperature Tensile Test
Jin WANG1, Yuefei ZHANG1(), Jinyao MA1, Jixue LI2, Ze ZHANG2
1 Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing 100124, China
2 Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310058, China
引用本文:

王晋, 张跃飞, 马晋遥, 李吉学, 张泽. Inconel 740H合金原位高温拉伸微裂纹萌生扩展研究[J]. 金属学报, 2017, 53(12): 1627-1635.
Jin WANG, Yuefei ZHANG, Jinyao MA, Jixue LI, Ze ZHANG. Microcrack Nucleation and Propagation Investigation ofInconel 740H Alloy Under In SituHigh Temperature Tensile Test[J]. Acta Metall Sin, 2017, 53(12): 1627-1635.

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摘要: 

利用自主研发的SEM原位高温拉伸台,研究了750 ℃高温条件下镍基高温合金Inconel 740H单轴拉伸变形过程中微观组织演变规律及微裂纹萌生与扩展机制。结果表明,在室温和高温条件下,Inconel 740H合金变形过程中晶界是主要的裂纹萌生源,但是在室温时微裂纹也会在晶内萌生。通过对原位变形机制的分析表明,750 ℃高温不仅降低了滑移系的开启能量,使更多的滑移系容易开动,而且弱化了晶界强度,使晶界具有弯曲和滑移的变形特性,从而增强了合金的塑性协调变形能力,但是却降低了合金的屈服强度和抗拉强度,高温同时也使合金晶界的相对强度弱化,导致微裂纹更易从晶界处萌生并扩展。

关键词 Inconel 740H原位扫描电子显微分析高温拉伸微裂纹萌生和扩展    
Abstract

As a result of increasing energy demands and accelerated environmental problems, there is an urgent need to improve the thermal efficiency of ultra supercritical (USC) power plants. To achieve this goal, advanced ultra-supercritical (A-USC) technologies with the main steam temperature of 700~750 ℃ and pressure of 35 MPa have been developed quickly in recent years. One of the most promising candidate Ni-based superalloys for the main steam pipe of 700 ℃ ultra-supercritical coal-fired power plants is Inconel 740H, which is a modified version of Inconel 740 developed by Special Metals Corp (SMC). Compared with IN740, the Ti/Al ratio in IN740H is lowered in order to stabilise the microstructure at long ageing times. In addition, the Nb content is lowered to improve the weldability. In this work, the microstructure evolutions, the nucleation and propagation mechanisms of microcracks in the nickel base superalloy Inconel 740H at 750 ℃ high temperature were studied by the self-developed in situ high temperature tensile stage inside a SEM. The results showed that under the uniaxial tensile stress at 22 ℃ room temperature and 750 ℃ high temperature conditions, the grain boundaries of Inconel 740H alloy are always the most primary crack sources. The strength of grain boundaries is higher than that of grains under the room temperature, and the microcracks will be nucleated at the grains as well, but the relative strength of grain boundaries will be weaken under the high temperature, which makes the microcracks tend to nucleate at grain boundaries. The experimental results also showed that the influence of high temperature on the mechanical properties is very significant, the high temperature reducing the activate energy of slip and weakening the strength of the grain boundaries, so that more slip systems activated and the grain boundaries occurring bending and sliding deformation, so further enhance the ability of plastic deformation of alloy. However, the reduction of relative strength of alloy grain boundaries leads to microcracks nucleation and propagation more easily from grain boundaries and lower the yield strength and tensile strength of alloy.

Key wordsInconel 740H    in situ SEM    high temperature tensile    microcrack nucleation and propagation
收稿日期: 2017-06-07     
ZTFLH:  TG132.3  
基金资助:国家重大科研仪器项目No.11327901
作者简介:

作者简介 王 晋,男,1988年生,博士生

图1  原位拉伸样品尺寸图
图2  原位高温拉伸台实物和扫描电镜原位拉伸台主要工作部分截面图
图3  Inconel 740H合金固溶时效处理后观察标距段显微组织的OM像、晶粒尺寸直方统计图、晶界和孪晶界形貌的SEM像、(NbTi)C和Cr23C6碳化物形貌的SEM像
图4  Inconel 740H合金在22和750 ℃下的原位拉伸力-位移曲线图
Test Yield Ultimate tensile Elongation
temperautre strength strength
MPa MPa %
22 797 1240 31.0
750 761 1132 45.6
表1  Inconel 740H合金在22和750 ℃下的原位拉伸力学性能
图5  Inconel 740H合金在22 ℃原位拉伸过程中不同载荷状态下微观裂纹萌生演变过程
图6  Inconel 740H合金在22 ℃原位拉伸过程中不同载荷状态下微观裂纹扩展演变过程
图7  Inconel 740H合金在750 ℃原位拉伸过程中不同载荷状态下微观裂纹萌生演变过程
图8  Inconel 740H合金在750 ℃原位拉伸过程中不同载荷状态下微观裂纹扩展演变过程
图9  Inconel 740H合金在22和750 ℃单轴拉伸应力作用下微裂纹萌生扩展示意图
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