Study On Deformation And Recrystallization Texture Of High Tungsten Composite Substrates Used For Coated Conductors

NiW alloys have the advantages of oxidation resistance and good lattice matching with the superconducting layer,which makes them the most widely used materials for YBa₂Cu₃O_7-?coated conductors.However,as the mechanical and magnetic properties of low tungsten NiW alloys is not satisfying,the cube texture formation of high tungsten NiW alloy is decreased,and the Ni10W texture is not suitable to be a textured substrate.It can be seen that the research of single layer substrate cannot meet the strong requirements for coated conductors.The preparation of the composite substrate is an effective way to obtain a high property substrate.The study of low-high tungsten composite substrates has been performed for years,and has been meanwhile developed to high-high tungsten composite substrates.In this paper,we have carried out the research on the preparation of Ni7W/Ni12W/Ni7W and Ni8W/Ni12W/Ni8W high tungsten composites.By the study of the key technologies of RABiTS,the effects of rolling and of the recrystallization heat treatment process on the formation of cube texture were discussed.This paper contains the following innovations:The formability of the composite ingot was improved by following with scanning electron microscopy?SEM?and energy dispersive spectrometer?EDS?.Based on this,the influence of intermediate heat treatment of different temperatures on recovery and recrystallization of Ni7W/Ni12W/Ni7W composites was analyzed using X ray diffraction ring?XRD?technology and electron backscattering diffraction?EBSD?.The results show that the composite intermediately annealed at 600? has a high cube texture of 95%?<10°?.The study on discovery and recrystallization microstructure shows that the rolling texture of the substrate intermediately annealed at 600? decreases significantly,while its content of cube orientation is increased.The initial recrystallization microstructure of the substrate intermediately annealed at600? has a higher cube texture content.In addition,its average size of the cube orientation is obviously larger too.The research of both deformation and recrystallization of cold rolled Ni8W/Ni12W/Ni8W composites shows that the transition to the brass type texture in Ni8W/Ni12W/Ni8W substrates begins at the thickness of 0.5 mm.During the initial recrystallization,cube orientation has no advantage neither in content nor in size.Intermediate heat treatments added at the thicknesses of 2mm,1mm,0.5mm and0.25mm had the best optimization effect.The comparison of the discovery microstructure of cold rolling and intermediately annealed substrate show that it is the shear that causes the deterioration of both deformation and recrystallization texture;the content of shear was greatly reduced and the volume fraction of S,Copper and Cube orientation was increased in intermediately annealed samples.Finally,during the optimization of the Ni8W/Ni12W/Ni8W recrystallization process,the cube texture increases with increasing holding time of the first step heat treatment.After700?/60min,the Ni8W/Ni12W/Ni8W composite substrates formed a cube texture of91.7%?<10°?.In summary,this work improved the strong cube texture content of Ni7W/Ni12W/Ni7W and Ni8W/Ni12W/Ni8W composite substrates.With the study of microstructure under different intermediate annealing and recrystallization processes,the optimization mechanism of intermediate heat treatment was analyzed.This study not only guides the subsequent manufacture of composite substrates,it also enriches the theory of intermediate annealing effect on low SFE FCC materials and on the cube texture formation mechanism.