| Austenitic stainless steels,such as 316/316 L,304/304 L,etc.are commonly used as structure materials in nuclear power plants.However,intergranular corrosion(IGC)and intergranular stress corrosion cracking(IGSCC)along the grain boundary has become the main form of failure in these materials after long-time service.Grain boundary engineering(GBE)technology,which can improve resistance to IGC and IGSCC of materials by optimizing grain boundary network,has the potential to be applied in the process of austenitic stainless steels.There are a large number of studies about GBE.However,most results of these studies are obtained through characterization and analysis on the two-dimensional(2D)slice of samples,which can’t fully reflect the situation of the grain boundary in the three-dimensional space.In this study,the distribution characteristics of the grain boundary plane(GBP)orientation in316 L stainless steel were studied by analyzing the 3D-EBSD data,and the influence of the GBE process on the grain boundary plane orientation distribution was discussed.The main results were list below.(1)The uniformity of grain orientation is the main factor that affects the analysis results of the tolerance of the twin boundary.The better the uniformity of the grain orientation,the smaller the tolerance of the twin boundary.The GBE promotes the multiple twinning process to form more twin boundaries both in terms of number and area.The tolerance of the twin boundary is higher in the GBE sample than that in the non-GBE samples,because of the poor orientation uniformity of grains in the GBE sample.In addition,there are more grains with similar orientation in the GBE sample.So the grain merger phenomenon is more likely to occur in the GBE sample,and the poor orientation uniformity of grain formed by merging also contributes to larger tolerance of twin boundary in the GBE sample.(2)The “direct approximation method” is more suitable for analyzing the orientation data of a single specific type grain boundary,whereas the “probing distribution method” is more suitable for analyzing the orientation data of a single grain boundary.The results obtained by “direct approximation method” show that the two twin boundary plane types with the highest proportions are {234}/{234} and{334}/{344}.(3)The GBPs of Σ3 are mainly distributed around {111}/{111}.Most of Σ3 are incoherent twins with {112}/{122}.The GBPs of Σ9 are mainly distributed along the[110] zone.The GBPs of Σ9 are mostly {114}/{114},{001}/{112},{111}/{115}.(4)The effect of GBE process on the distributions of GBPs of Σ3 and Σ9 grain boundaries in 316 L stainless steel was studied.The results show that although the GBE process increases the overall proportion of twin boundaries,it does not increase the proportion of incoherent twin boundaries in all twin boundaries.On the contrary,the proportion of coherent twin boundaries in GBE sample was lower,that is,the GBE process promoted the formation of incoherent twin boundaries.After GBE treatment,more Σ9 grain boundaries were formed in the sample,but the distribution of Σ9 GBPs was more dispersed.In addition to the [110] zone,Σ9 grain boundary with {111}/{112}is also formed.The both fraction of the tilt and the twist grain boundary in the GBE sample are slightly lower than that in non-GBE samples,which indicating that the multiple twinning process promotes the formation of mixed type grain boundaries.(5)The sphericity,aspect ratios and grain boundary plane approximation of the grains in the annealed 316 L stainless steel obeys the normal distribution,Beta distribution and Gamma distribution,respectively.The sphericity and aspect ratios of the grains in the GBE sample are larger than that in non-GBE samples.The plane proximation of the grain boundary in GBE sample is lower than that in non-GBE samples. |
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