AFM Observation On Martensitic Surface Relief And Research On Its Crystallography And Morphology

The surface reliefs of lath martensites, {225 }f and {259}f martensites are compared based on AFM abservation and measurement (with assistants of SEM and optical microscope) in this paper. As a result, the surface reliefs of lath martensites are found to have an arc appearance , which embodys the rotation of the martensites , the least width and the largest change interval of measured list angles ;While the surface reliefs of {259}f martensites have normal "N" appearance , which embodys the good self-accommadation ability ,the biggest width value and the most stable measured list angles;As for the surface reliefs of {225}fmartensites ,all of the guidelines above are in the middle of those for {557}f and {259}f martensitic surface reliefs. Many smaller N-like reliefs are also found to form the macro surface reliefs which gives us the message that the surface reliefs are formed by sub-unit shear. Then we can make the conclusion that lath and {225 }f martensites don t have an invariant plane because their parent phase has high distortion ability which can be used to accommodate the crystall lattice deformation during phase transformation and gives reason to the occurrence of sub-units;while the parent phase of {259}f martensite has high intensity which leads to the formation of twins .As well known ,twins can self-accommodate well,so that one plane of {259}f martensite can be kept stably is easy to be learned. Some direct experiment results also show that the ability of keeping habit plane invaiantly for lath martensite is the worst, that for {259}f and {3,10,15}f martensites are the best, and that for {225 }f martensite is in the middle.With the photos and measurement results of martensitic sub-structure ,habit plane and direction relationship with parent phase taken by TEM and the analysis on martensite habit plane and its forming principle based on "displacement vector" theory,conclusion can be made that there are sub-units in {557}f and {225 }f martensites one side of which forms the macro martensite habit plane. The predicted results of martensitic microscopic and macroscopic habit planes based on "displacement vector" are in agreement with the experiment results.On research of martensitic morphology,some criterions can be found: such as,some materials which is known to ought to produce twin martensite can have dislocation sub-structure martensites in its phases if it is compressed.Let the material which has had martensite phase transformation once keeping at normal temperature for some time and then cool it to make the martensite phase transformation takes place once again,then some new morphology martensites maybe be found in the material.Conclusion taken form above is that the strcture state of parent phase can do direct result to the martensitic morphology.