| Morphology, surface relief effect, and transformational shear angle of (259}f martensite, lath martensite and {225}{ martensite in iron-based alloy, by means of Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM), and Light Optical Microscope, were intensively investigated in this paper; based on Displacement Vector Theory's calculation, martensite's habit plane and its rotation were predicted; the relationship between self-accommodation of different variants, martensite morphology, surface relief morphology, and "invariant plane" were also discussed.It's shown that heat treatment processing and pre-deformation of parent phase both had quite an effect on the morphology of martensite and its surface relief in Fe-23Ni-0.55C alloy. With the increasing of austenizing temperature, martensite plate changed from thin and long shaped to lenticular shaped, as well as its boundary from flat to curved. Correspondingly, the morphology of its surface relief turned from long-plate shaped to short-plate shaped, as well as its boundary from flat to banded. When compressive deformation of parent phase was reaching 30 percent, martensite plates of Fe-23Ni-0.55C alloy were arrayed as thin "packets", parallel to each other, and the same as its surface relief. In addition, for the severe distortion of parent lattice, not only the boundary was ragged, but also its midrib was fragmental or banded.Surface reliefs AFM observation and quantitative analysis of {259}f martensite and lath martensite was performed, and surface reliefs ultra-microscopic structure of (225}f martensite, for the first time, was quantitatively analyzed. It demonstrated that self-accommodation between different variants of {259}f martensite could approximately be fulfilled, and consequently, its surface relief was regular relief, formed by Invariant Plane Strain (IPS), appearing to be "N"-shaped or tent-shaped. Incapable of self-accommodate, surface relief of lath martensite was formed through plastic-accommodation between new and parent phase i.e. surface relief cluster of lath martensite was formed by surface relief "packets", and "packet" was further formed by several single surface relives. That surface relief "packets" was irregular "N"-shaped and its single surface relief was tent-shaped indicated that surface relief of lath martensite wasn't formed by homogeneous deformation and not to be IPS-type. Surface reliefs formation of (225}f martensite was resulted from both self-accommodation and plastic-accommodation. When deep cryogenic treated at the lower temperature, surface relief of (225}f martensite wasirregular "N"-shaped, composed of some small sub-units (or small surface relives), just like that of lath martensite. However, its small sub-units were not as fluctuating as the small surface relives in surface relief "packets" of lath martensite. Upon the higher temperature deep cryogenic treatment, the formerly formed surface relief of {225} f martensite was still irregular "N"-shaped, with one side being flat and smooth, while the other side being curved. In addition, beside the formerly formed surface relief, several small surface relives, arrayed parallel to each other, could be seen, and the angle between the formerly formed surface relief and the parallel small surface relives was about 30 . Furthermore, the even smaller surface relives were arrayed on both sides of the small surface relief, too.Calculation methods to determine (259}f martensite and lath martensite's shear angles were established in this paper. It showed that the AFM determined shear angles of different variants of {259}f martensite were in agreement with the prediction of W-L-R theory, with the deviation being less than 3.256 ; the AFM determined shear angle of lath martensite was in agreement with the prediction of K-S model, with the deviation being less than 3.031 .The reason why PTMC was unable to predict transformation of {225}f martensite and lath martensite was intensively analyzed, and, by means of Displacement Vector Theory, habit planes and...
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