The Research Of A Modified BM Method For Martensitic Transformation

The crystallography of martensitic transformation described the orientation relationship between parent and martensite phase.And it described the process of the change of crystal structure when happened phase transformation.It was the core of martensitic transformation.The phenomenological crystallographic theory for martensitic transformation was based on the Bain model.It was one of the earliest model which explained the lattice reorganization.The model could obtain martensitic structure only by one strain and the atomic moving distance was the shortest.In this paper,the classical BM theory was introduced.In the light of the defect,the process of calculation of the original BM theory was improved by using calculation of vector,so that the process of calculation was easy and intuitive.Two kinds of the crystallography of martensitic transformation of DO3-M18R and B2-M9R in Cu-Zn-Al alloy were calculated by using improvement BM theory.The habit plane of martensitic transformation of DO3-M18R was((?) 0.6804 0.6996)by calculation and the experimental result was((?) 3.40 3.53),so deviation angle was 1.1109° and they were very consistent.The habit plane of martensitic transformation of B2-M9R was((?) 0.3752 (?))by calculation and the experimental result was((?) 6.88 (?)),so deviation angle was 3.6980° and they were basically consistent.The results of other crystallographic parameters calculated with improvement BM theory and traditional BM theory were basically same.This paper analyzed the change of volume before and after the martensitic transformation.There were twenty-four kinds of crystallographic equivalence of martensitic variants of parent phase in Cu-Zn-Al shape memory alloy.According to the phenomenological theory,the volume contraction of single martensitic variant could be found.But the actual volume of martensite was slightly swollen.So self-accommodation effect existing among martensitic variants was very important and it must be taken into account when we analyze the change of volume before and after the phase transformation.