The Influence of Cold-Rolling and Heat Treatment to the Annealing Twins and Mechanical Property in the CoCrFeMnNi High-Entropy Alloy
The properties of CoCrFeMnNi high entropy would be affected by annealing twins which formed during the anneal,and the microstructure and types of twins were influenced by the cold deformation degree and heat treatment.This research was designed to study the influences of deformation degree to the twins.FCC single phase CoCrFeMnNi high entropy alloy was prepared by vacuum medium frequency induction melting furnace.The samples in different deformation were obtained by cold-rolling after homogenizing annealing,then the samples were annealed at 900℃for 1 h.The microstructure characterization of annealing twins in the samples was obtained by optical microscope,X-ray diffraction and transmission electron microscope,and the static uniaxial tensile test at room temperature.The effects of deformation on annealing twins and the changes of mechanical properties before and after annealing were studied.The results show that the 30%deformation sample gets large grain size with a small number and variety of annealing twins.The grain size of 80%deformation sample is similar to the sample with 30%deformation,but the number and type of annealing twins are maximum.The 50%deformation sample shows the smallest grain size with medium quantity and variety of annealing twins.The tensile strength,getting from the tensile test,of the samples without heat treatment was positively correlated with the deformation degree and the highest tensile strength was 1 333.44 MPa,while the tensile strength was negatively correlated with the deformation degree after annealing at 900℃×1 h and the highest tensile strength was 585.81 MPa.The result shows that the CoCrFeMnNi high entropy alloy shows satisfying phase stability.The FCC structure was invariable during the cold-rolling and anneal without precipitated phase.The cold deformed samples appeared recrystallization after anneal,which causes the change of grain size,the quantity and variety of annealing twins and the mechanical property.At the same time,the ability of storage dislocation in alloy gets stronger due to the small-sized annealing twins.
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