| In this work,the FeCoNiCuMn high entropy alloy was selected as the research object which has the excellent plasticity.The X-ray diffraction(XRD),scanning electron microscope(SEM),hardness test and room temperature tensile test were used to investigate the microstructure and mechanical properties from two aspects.Firstly,the effect of the cold rolling on the microstructure and mechanical properties of the FeCoNiCuMn high entropy alloy was explored;and then the effect of annealing time(holding at 900℃ for 10min,20min,30min,45min,60min,90min,120min,respectively)and strong magnetic field(12T/MD//RD)on the microstructure and mechanical properties of FeCoNiCuMn high entropy alloy(90%cold-rolled reduction)was studied.The as-casted,homogenized and cold rolled FeCoNiCuMn high entropy alloy all were composed of two kinds of the FCC structure,they are the matrix phase FCC1 and the Cu-rich phase FCC2.The microstructures of the as-casted and homogenized FeCoNiCuMn high entropy alloy are typical dendrite DR and inter-dendritic ID.But the composition of the sample is even more uniform after homogenizing;the content of Cu in the Cu enriched phase is lower than that of the as-casted state.The Cu enriched phase in the cold-rolled alloys is elongated and the slight wave shape appeared with increasing the cold rolling reduction.The content of Cu in the Cu enriched phase decreases with increasing the cold rolling reduction.The hardness values of as-casted and homogenized FeCoNiCuMn high entropy alloy is lower.In cold rolling process,the hardness value of the sample increases with increasing the cold rolling reduction.To compare with the as-casted sample,the yield strength and tensile strength of cold rolled sample are nearly linear growth trend with increasing the cold rolling reduction.And then the effect of processing hardening is obvious.The tensile fracture morphology of the as-casted and homogenized FeCoNiCuMn high entropy alloy are mainly dimples,and the main deformation mechanism is ductile fracture.The tensile fracture morphology of the cold rolled sample has the dissociation features,it shows the coexistence of brittle fracture characteristics and ductile fracture characteristics.The microstructure of the 90%cold rolled FeCoNiCuMn high entropy alloy was always composed of two kinds of FCC phase structures after heat treatment with different holding times;and the phase structure is not affected by the strong magnetic field,but the strong magnetic field affects the evolution of the texture of the alloy.With the increasing of annealing time,the content of Cu in the Cu enriched phase decreases significantly,the strong magnetic field has the characteristic of making the composition more uniform in the annealing process.Complete recrystallization of the alloy occurs when the holding time of annealing process is 90min without the strong magnetic field,and the size of grain is about 15μm.Complete recrystallization of the alloy occurs when the holding time of annealing process is 120min with the strong magnetic field,and the size of grain is about 7-10μm.The strong magnetic field can inhibit the recrystallization process of the alloy.The hardness values of the 90%cold rolled FeCoNiCuMn high entropy alloy was decreasing trend after heat treatment with different holding times.With the increasing of annealing time,the hardness of the sample is changed slowly by the strong magnetic field annealing,and the yield strength and tensile strength of the sample decrease in tensile test.The tensile fracture morphology of the specimen is mainly in the form of dimple,and the cleavage characteristics gradually disappear,which is characterized by ductile fracture.In general,the strong magnetic field annealing has little effect on the change of hardness and tensile fracture morphology of the specimen.Comparison of macroscopic texture of the 90%cold rolled FeCoNiCuMn high entropy alloy after heat treatment with holding l0min,the sample is mainly recrystallization texture without the strong magnetic field.Under the action of the strong magnetic field,the recrystallization texture and deformation texture coexist,which means that the strong magnetic field can inhibit the process of the recrystallization. |
