INTERPHASE BOUNDARY STRUCTURE AND HABIT PLANE OF LENTICULAR MARTENSITE IN IRON-BASED ALLOYS

在铁基合金中，随着温度的降低，马氏体的形貌由板条状变为透镜状和薄板状。为了弄清马氏体形貌变化的原因，本研究以Fe-Ni合金为主要材料，采用透射电镜对其亚结构和晶体学特征（如习惯面、取向关系、相间边界结构等）进行了详细观察。主要研究结果如下：透镜状马氏体板由三部分组成，即(1)完全孪晶的中肋，(2)从中肋延伸出孪晶的孪晶区，(3)含有高密度位错的未孪晶区。中脉是相变开始的区域，具有与薄板马氏体相同的形貌（薄板）和结晶学（{3,10,15}习惯面，G-T取向关系）。透镜状马氏体的取向关系为G- s，在中肋处多为T，在M/A界面处逐渐向K-S方向偏移。这种变化与马氏体亚结构的变化有关。虽然透镜状马氏体的界面在光学显微镜尺度上通常是光滑的，但在接近室温时，随着Ms温度的升高，界面变得不规则，并呈现出许多{225}A面。{225}A面对应于板条马氏体的习惯面。透镜状马氏体的相界面由两组可容纳相变应变的螺位错组成。这种边界结构与板条马氏体相同。结果表明，相变过程中晶格不变剪切模式的改变是马氏体形貌变化的主要原因。当发生孪晶时，马氏体形态变为薄板状；当发生滑移时，马氏体形态变为板条状。在生长过程中，当晶格不变剪切由孪晶变为滑移时，马氏体的形貌变为透镜状。少

In iron-based alloys, the morphology of martensite changes from lath to lenticular and thin plate with a decrease in Ms temperature. In the present study, in order to make clear the reason of martensite morphology change, substructure and crystallographic features such as habit plane, orientation relationship, interphase boundary structure, etc) were observed in detail by means of transmission electron microscopy using mainly Fe-Ni alloys. Main results obtained are as follows.1.Lenticular martensite plate consists of three parts, i.e., (1)the mid-rib which is completely twinned, (2)the twinned region in which some twins are extended from the midrib, (3)the untwined region which contains a high density of dislocations. Midrib is the region at which the transformation is initiated, and has the same morphology (thin plate) and crystallography ({3,10,15}habit plane, G-T orientation relationship) as those of thin plate martensite.2.The orientation relationship of lenticular martensite is G- … More T at the mid-rib but gradually deviates towards K-S near the M/A interface. This change is related to the change in the substructure of martensite.3.Although the interface of lenticular martensite is usually smooth in the scale of optical microscopy, it becomes irregular when the Ms temperature is increased near room temperature, and exhibits many {225}A facets. The {225}A plane corresponds to the habit plane of lath martensite.4.The interphase boundary of lenticular martensite consists of two sets of screw dislocations which accommodate transformation strain. This boundary structure is same as that of lath martensite.5.It was concluded that the change of marteniste morphology results from the change in the mode of lattice invariant shear during transformation. Martensite morphology becomes thin-plate when the twinning occurs, and the lath shape when the slip occurs. When the lattice invariant shear changes from twinning to slip during the growth, morphplogy of martensite becomes lenticular. Less