Delidon R. Regularities of martensitic transformation in melt-quenched iron-nickel alloys.

The regularities of grain structure formed under high temperature gradients during quenching from the melt, and its impact on the characteristics of martensitic transformation in local areas of thin films iron alloys were investigated in thesis. For quenching from the melt were used the following two ways: melt-spinning and quenching from laser melt. These two methods differed in rate of cooling during hardening of thin ribbons. Due to substantial texture of the structure of studied ribbons, the accurate calculation of martensitic phase by known methods was difficult, and in some cases impossible. Therefore, we have proposed a method for calculation of martensitic phase of textural iron alloys. The idea of this method was to measure the quantity of martensitic phase by diffraction method in textural alloys using the ratio of integrated intensity of diffraction austenitic and martensitic reflections that are parallel according to the crystallographic orientation of the ratio between crystallographic planes of austenite and martensite. The proposed method has allowed for the first time to solve the problem of measuring the amount of martensitic phase in local areas of textural alloys. Measurements have showed that the completeness of martensitic transformation was different for different sides of the ribbon. The main factor that influenced on the heterogeneous distribution of martensitic phase in local areas of the ribbon was grain size effect of martensitic transformation. It was found, that in contrast to the thin ribbons in the area of laser melt quenching, the distribution of martensitic phase was influenced not only by grain size effect, but also by residual stresses. Grain size effect in direct martensitic transformation influenced the course of reverse transformation in thin ribbons. This is explained by the presence of ultrafine (1.0 - 0.5 microns) component of austenitic grains, which in turn, determines the higher stabilization of austenite of rapidly quenched alloys by cyclic a-y-a martensitic transformation compared to the massive alloys of the same chemical composition. Gradient distribution of martensitic phase in thin ribbons has allowed to create a sort of sandwich that can be regarded as a miniature seamless bi-phase plate with thermo bi-metal properties.