Fe—1．83C马氏体中碳的有序化　Ⅱ．长周期有序相的晶体结构

CARBON ORDERING IN Fe-C MARTENSITE Ⅱ. Crystal Structure of Long-Period Ordered Phase

Ｆｅ－１．８３Ｃ马氏体在室温时效时，超点阵衍射斑点发生分裂，表明产生了长周期有序相。分析确定该相由普通有序相γ′—ＦｅｘＣ（Ⅰ）衍生而来，周期为１０ｃ＿Ｍ（ｃ＿Ｍ为马氏体ｃ轴的长度），称为γ′—ＦｅｘＣ（Ⅱ）（ｘ＝４—１０）．其周期不随时效时间变化，但随温度升高而增加。超点阵斑点的分裂距离所对应的长周期不是ｃ＿Ｍ的整数倍，表明周期为１０ｃ＿Ｍ，１２ｃ＿Ｍ，１４ｃ＿Ｍ的３种长周期有序结构可能同时存在，其衍射线互相干涉使超点阵斑点的分裂距离不为ｃ＿Ｍ的整数分之一。根据本研究确定的长周期有序相的晶体结构，计算出的电子衍射强度与实验观测值完全符合。本文还讨论了普通有序相γ′—ＦｅｘＣ（Ⅰ）与长周期有序相γ′—ＦｅｘＣ（Ⅱ）的相互关系。

Split superlattice reflections are detected in Fe-1 .83C martensite aged at room temperature, indicating the existence of long-period ordered phase. The long-period phase is superperiod of 10 c_M(c_M being the length of c axis of martensite), it is named as γ′-FexC(Ⅱ). For the first time it is found that the superperiod of this long-period phase increases with the increase of temperature, but does not change with aging time. It is also found that the superperiod calculated from the split distance of superlattice spots is not an integral multiple of C_M This is an indication of the coexistence of three long-period ordered phases with superperiod of 10 c_M 12 and 14 c_M, respectively, the interference of diffraction beams from them results in the non-integrality of the split distance of superlattice spots.The calculated intensities of the superlattice reflections are in good agreement with experimental observations. It is suggested that the existence of long-period ordered phase is a result of minimization of lattice distortion energy. The relationship betweenγ′-FexC(Ⅰ) and γ′-Fex C(Ⅱ) is also discussed.