Recently, high entropy alloys have attracted the attention of researchers due to their suitable mechanical, physical, corrosion and wear properties. Based on this, it is extremely important to study the different properties of these alloys in order to further develop them. The purpose of this research is to investigate the strengthening mechanisms in cold rolling and annealing on FeCoCrNiMn high entropy alloy. Therefore, the FeCoCrNiMn high entropy alloy was first made by induction melting under vacuum. Then, in order to remove the casting structure, homogenization was performed on this alloy. In order to obtain the appropriate temperature and time for homogenization, experimental design and the response surface method were used, and a model for appropriate temperature and time conditions was presented. The suitable temperature and time conditions for the destruction of the casting structure and the minimization of the separation were obtained at a temperature of 1100 degrees Celsius and a time of 15 hours. Also, in order to investigate the effect of rolling on the microstructure on the alloy, cold rolling was performed on the samples with a thickness reduction of 35, 45, 75 and 85%, respectively. In order to check the mechanical properties, tensile, hardness, fracture and wear tests were used at room temperature. Also, microstructural and phase investigations were carried out with the help of optical microscope, scanning electron microscope and X-ray diffraction test. The fracture surfaces were checked by scanning electron microscope and in order to eva‎luate corrosion properties, Tafel test was used at room temperature and in 3.5% sodium chloride solution. By X-ray diffraction test, it was determined that the alloy has a single FCC phase, which was not observed due to the homogenization of the new phase in the structure. The density of dislocations was calculated using X-ray diffraction test data. It was observed that as a result of cold roll on the samples, the density of dislocations increased from 4.6 × 1012 per square meter to 2.2 × 1015 per square meter. The results of the tensile test at room temperature showed that the tensile strength increased from 437 MPa for the homogenized sample to 1260 MPa in the cold rolled sample with an 85% reduction in thickness. Also, by examining the fracture surface of the tensile test samples, it was found that with the increase in rolling percentage, the area of the dimples decreased from 38 micrometers in the homogeneous state to 11 micrometers in the 85% cooled rolling state. In addition, due to the increase in the percentage of rolling, the hardness of the alloy increased up to 3 times of the homogenized state from 150 Vickers in the homogenized state to 450 Vickers in the cooled sample with 85% thickness reduction. Also, strengthening due to the increase in the density of dislocations was introduced as the most important factor in increasing the strength of this alloy in the cold rolling state. The workability of FeCoCrNiMn alloy was calculated by extrapolating the strain stress diagram between the yield and tensile points. Hard work power decreased from 0.32 in homogeneous state to 0.10 in 85% rolled state. Then, with the help of experimental design and method, the temperature response level and recrystallization annealing time were calculated. After the recrystallization annealing process on the rolled samples, the grain size was reduced by the static recrystallization mechanism from 220 micrometers in the homogenized state to 14 micrometers in the 85 cold rolled and annealed state. The wear behavior of rolled and annealed samples was compared using the pin-on-disk wear test. The results of the wear test showed that the wear mechanism is mainly scratch wear. Comparison of 85% and 45% cold rolled samples showed a decrease of about 20% in friction coefficient from 0.86 to 0.64 and from 0.72 to 0.54 respectively after annealing.

مهدي علي زاده , مسعود عطاپور

قاسم ديني , بهزاد نيرومند , محمد رضايت