Object kinetic Monte Carlo study of the effect of grain boundaries in martensitic Fe–Cr–C alloys
Object kinetic Monte Carlo study of the effect of grain boundaries in martensitic Fe–Cr–C alloys
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马氏体 Fe-Cr-C 合金中晶界影响的物体动力学蒙特卡罗研究
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发表时间：
2016
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通讯作者：
C. Becquart
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作者：
M. Chiapetto;L. Malerba;A. Puype;C. Becquart
铬浓度在 ∼2 至 12%wt.% 范围内的 Fe-Cr-C 合金通过在碳浓度相对较低的情况下从奥氏体状态快速冷却形成铁素体-马氏体结构。在此过程中，通过改变热处理可以获得不同比例的铁素体和马氏体以及碳化物的形成。铁素体或马氏体的存在可能会对这些合金在辐照下的纳米结构演变产生影响。在这里，考虑含 9% Cr 的回火马氏体参考合金，我们利用已经验证的物体动力学蒙特卡罗 (OKMC) 模型来研究中子辐照下马氏体板条的形成对材料纳米结构演化的可能影响，假设相关边界充当辐射缺陷的汇。结果表明，晶粒尺寸（在此定义中包括原奥氏体晶粒、包、块和板条的平均尺寸）的减小在尺寸达到约 0.5μm 之前不会发挥任何相关作用：对于较小的晶粒，被边界吸收的缺陷数量占主导地位。然而，这个阈值低于实验观察到的马氏体板条尺寸，从而表明马氏体 Fe-Cr-C 合金相对于铁素体的差异，涉及辐照期间发生的事件和机制，并不是作为汇的板条边界。因此，铁素体和马氏体在中子辐照下纳米结构演化之间的差异应归因于其他因素。
Fe–Cr–C alloys with chromium concentrations in the range from ∼2 to 12 wt.% form ferritic‐martensitic structures by rapid cooling from the austenite state already in the presence of relatively low carbon concentrations. In this process it is possible to obtain different ratios of ferrite and martensite, as well as formation of carbides, by varying the thermal treatment. The presence of ferrite or martensite might have an influence on the nanostructural evolution under irradiation of these alloys. Here, considering a tempered martensite reference alloy with 9% Cr, we make use of an already validated object kinetic Monte Carlo (OKMC) model in order to study the possible effect of the formation of martensite laths on the material nanostructural evolution under neutron irradiation, assuming that the relevant boundaries act as sinks for radiation defects. The results show that the reduction of the grain size (including in this definition the average size of prior austenite grains, packets, blocks, and laths) does not play any relevant role until sizes of the order of ∼0.5 µm are reached: for smaller grains, the number of defects being absorbed by the boundaries becomes dominant. However, this threshold is lower than the experimentally observed martensite lath dimensions, thereby suggesting that what makes the difference in martensitic Fe–Cr–C alloys with respect to ferrite, concerning events and mechanisms taking place during irradiation, are not the lath boundaries as sinks. Differences between the nanostructural evolution under neutron irradiation in ferrite and martensite should therefore be ascribed to other factors.