Study on Evolution of Grain Boundary Composition in Nickel Based Alloy 690
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摘要: 采用原子探针层析(APT)技术研究晶界碳化物析出之前杂质或溶质原子在690合金晶界处的偏聚规律,并采用配备在高分辨透射电子显微镜(HRTEM)上的能谱(EDS)设备研究晶界碳化物析出之后690合金晶界处的成分演化规律。结果表明:在晶界碳化物析出之前,C、B、Si等原子偏聚在晶界处,同时C与Cr共偏聚在晶界处,晶界富Cr;碳化物析出之后,晶界处Cr浓度越来越低,在715℃时效15 h后晶界处Cr浓度达到最低值,然后随着时效时间的延长Cr浓度逐步提高;当碳化物基本覆盖整个晶界后晶界富Cr;除了晶界处Cr贫化程度外,晶界处贫Cr区内的Cr浓度梯度也是影响晶界耐腐蚀能力的主要原因。Abstract: The solute and impurity atoms segregation at grain boundaries before carbide precipitation in Alloy 690 were examined by atom probe tomography.The evolution of grain boundary chemistry after carbide precipitation in Alloy 690 was examined by X-Ray energy dispersive spectrum adapted at high resolution transmission electron microscopy.C,B and Si atoms segregation,C and Cr co-segregation,and Cr enrichment at grain boundaries were observed before carbide precipitation at the grain boundaries.The chromium depletion zone formed at the grain boundaries after carbide precipitation.The chromium concentration at grain boundaries decreased with the aging time prolonging.The chromium concentration at grain boundaries reaches the minimum value after aging at 715℃ for 15 h.And then,the chromium concentration at grain boundaries increased with the aging time prolonging.After the carbides were fully covering the grain boundaries,the enrichment of chromium at grain boundaries can be observed.The chromium depletion zone,especially the chromium content gradient in the chromium depletion zone was the main factor that influenced the corrosion resistance of the grain boundary in alloys with high chromium content.
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