核反应堆压力容器(RPV)模拟钢样品经过660 ℃调质处理和370 ℃时效3000 h后, 用原子探针层析法研究了晶界和相界面上原子偏聚的特征. 结果表明, Ni, Mn, Si, C, P和Mo在晶界处均有不同程度的偏聚, 偏聚倾向由强到弱依次为: C, P, Mo, Si, Mn和Ni. Cu在晶界处会出现贫化现象. Si在晶界上的偏聚程度与晶界的特性有关. 在这几种元素中, C在晶界上偏聚的宽度最大, 如以成分分布图中浓度峰的半高宽来比较, C的偏聚宽度是Mn, Ni和Mo的1.5倍. 在富Cu相与 α-Fe的相界面处, Ni和Mn有明显的偏聚, 而C, P, Mo和Si倾向偏聚在相界面的α-Fe一侧, 且偏聚的程度比晶界处的低.
The segregation of impurity or solute atoms to grain boundaries as well as phase interfaces can either improve or degrade the chemical, physical and mechanical properties of alloys. This phenomenon has been studied widely for iron based alloys, and the analysis method by an atom probe tomography (APT) is a powerful tool for better understanding this problem. The resulting composition changes of grain boundaries and phase interfaces, as well as the precipitation of Cu-rich nanophases, are frequently associated with the phenomenon of embrittlement in ferritic reactor pressure vessel (RPV) steels. The present work was carried out to study the segregation of impurity or solute atoms to grain boundaries as well as phase interfaces in a RPV model steel with higher content of Cu (0.53%, atomic fraction) than commercially available one. The RPV model steel was prepared by vacuum induction melting. The specimens were further heat treated by water quenching at 880 ℃ for 30 min and tempering at 660 ℃ for 10 h, and finally aged at 370 ℃ for 3000 h. The results show that the segregation amount of Ni, Mn, Si, C, P and Mo atoms on grain boundaries are varied. The sequence of segregation tendency for different atoms from strong to weak is C, P, Mo, Si, Mn and Ni, whilst Cu atoms were clearly depleted at the grain boundaries. Si atoms also segregate to the grain boundaries, but it depends on the characteristic of the grain boundaries. The C segregation range at grain boundaries is the widest. According to the width of the composition profiles at the half intensity for different atoms at the grain boundaries, the segregation range of C atoms is 1.5 times wider than that of Mn, Ni and Mo atoms. Furthermore, Ni and Mn atoms evidently segregate to the interfaces between the Cu-rich phase and the α-Fe matrix, while C, P, Mo, Si atoms prefer to segregate towards the α-Fe matrix near the interfaces, but their segregation amount at the interfaces of Cu-rich phase and the α-Fe matrix is less than that at the grain boundaries.
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