Characterization Of The Microstructure Of Copper-steel Composites

In recent years,the particularity of martensitic transformation in nano-materials(monomeric materials or materials with the grain size being less than 100nm)has caused great concern of scientists.Industrial steels must be heated to a high temperature(above 750?)for austenitizing in martensitic transformation,so it is difficult to obtain nanoscale grains.Therefore,so far,there are rarely studies or reports on the characteristic of martensitic transformation in nanoscale steels.In this thesis,copper/T10 steel and copper/65 Mn steel composite wires with the thickness of slice being in nanoscale are obtained by the method of hot pressing and severe deformation including rolling and drawing with the raw material are copper,T10 steels and 65 Mn steels.And the microstructure of the composites is observed by transmission electron microscopy(TEM)and other advanced experimental techniques.Copper-steel nano-laminated composite wires are successfully made by method of hot pressing and severe deformation including rolling and drawing.The retained austenite is obtained by quenching-partitioning,and its content is about 51%.The results of tensile test show that the composites have significant stress and strain-induced martensitic transformation with high work hardening ability.The microstructure of this composites and the relationship of orientation between phases are systematic characterized by TEM.Results show that the average thickness of the component sheets in copper-steel composites is about 88.5nm.In accordance with the angle of nanoscale martensite twins and the interface,the morphology of martensite can be divided into three categories,“45 degrees” martensite,“90 degrees” martensite and “cross-martensite”,and all of them mainly exist in the form of a single variant.The retained austenite with the morphology being like film is alternately spaced with martensite sheets,and the average thickness is about 7nm.There are two kinds of orientation relationship between copper phase and martensite,one is [001]Cu?[001]M,(020)Cu and((?)10)M are nearly parallel,and the other is [011]Cu?[001]M,(11(?))Cu?(110)M.The orientation relationship which mostly rendered between martensite sheets is [001]M1?[(?)11]M2,(110)M1?(110)M2.The orientation relationship which mostly rendered between retained austenite and martensite is [(?)13]M?[011]RA,(110)M and((?)00)RA are nearly parallel.The average thickness of the pearlite sheets in copper/65 Mn steel layered composite wires is less than that in conventional large-sized pearlite,and the interface between ferrite and cementite is flatter and straighter.