Effect Of Directional Solidification On The Microstructure And Mechanical Properties Of Multi-component CuCrFeNiMn Alloy System

In the field of alloys,the multi-element high-entropy alloy is an emerging field.Since Jien-Wei Yeh et al.put forward its alloy design concept in 2004,it has aroused the concern of researchers.Multi-element high-entropy alloys are usually composed of five or more main elements and secondary elements with equal or close to equimolar ratios,and they are generated by the relatively high mixing entropy to form a new solid solution phase.This alloy concept breaks the traditional alloy design pattern,and it has excellent performance through the selection of elements.At present,the study of multi-element high-entropy alloy is still in its infancy,and thus the relevant theoretical system also needs to be improved.Directional solidification technology can effectively reduce the alloy composition segregation,loose tissue and other casting defects as well as the elimination of horizontal grain boundaries,and the performance of the alloy can be improved significantly.The research on directional solidification high entropy alloy is very rare,and therefore this paper will use directional solidification technology to optimize the performance of high entropy alloy.In this paper,Cu_0.3Cr₂Fe₂Ni₃Mn₂ multi-element alloy was prepared by arc melting,and the performance of the alloy was optimized by directional solidification.The effects of different extraction rates?5?m/s,10?m/s,30?m/s,150?m/s?on the microstructure and mechanical properties of the alloys were investigated.The effects of Ti and Zr on the microstructure and mechanical properties of Cu_0.3Cr₂Fe₂Ni₃Mn₂ multi-element alloy were also studied by through the alloy element selection.In addition,the paremeters of?S_mix,?H_mix,?and VEC were calculated to predict the structure and phase stability.The results showed that the FCC crystal structure was mainly present in as-cast and directionally solidificated Cu_0.3Cr₂Fe₂Ni₃Mn₂ alloys,The?200?diffraction peak strength of the alloy after directional solidification became very strong with the withdrawal rates of 5?m/s and 10?m/s,which indicated that strong texture may be formed after directional solidification;The intensity of?200?diffraction peak decreased and the?111?diffraction peak increased at 30?m/s and 150?m/s,.The alloying structure was mainly composed of dendrites and intergranular.The EDS spectra showed that the Cu,Ni and Mn were rich in intergranular and theCr and Fe were rich in dendrites.The alloy composition difference became smaller and tended to be homogenized after directional solidification.When the orientation was 5?m/s,the elongation of the alloy was58%which was more than 26%higher than that of the as-cast and the tensile strength and yield strength remain almost unchanged,With the increase of the withdrawal rate to 10?m/s,the elongation reached 66%,but the tensile strength and yield strength decreased.The hardness decreased slightly after directional solidification,and the fracture mode of the alloy was ductile fracture.After the addition of Ti element,the Cu_0.3Cr₂Fe₂Ni₃Mn₂Ti_0.5 high entropy alloy was composed of FCC+small amount of BCC solid solution.With the increase of Ti concent,Cu_0.3Cr₂Fe₂Ni₃Mn₂Ti_1.0 high entropy alloy was consisted of FCC solid solution,BCC solid solution and Ni₃Ti intermetallic compounds.Microstructure was a typical dendritic structure,and EDS spectrum showed that Ti elements mainly distrubuted in the intergranular.The hardness of the alloy increased with the increase of Ti content,and the hardness of Cu_0.3Cr₂Fe₂Ni₃Mn₂Ti_1.0 alloy was up to 550.9 HV.Due to the presence of intermetallic compounds,the alloy was hard and brittle.Cu_0.3Cr₂Fe₂Ni₃Mn₂Ti_0.5 alloy presented good tensile properties.The yield strength was 311.82 MPa,and the tensile strength was up to720.75 MPa with an elongation of 15%.After directional solidification,the comprehensive performances of Cu_0.3Cr₂Fe₂Ni₃Mn₂Ti_0.5 with a withdrawal rate of 30?m/s were good,Due to the addition of Ti,the tensile strength was 626.60 MPa,and the elongation of the alloy was 18%which was 17%higher as compared to the as-cast.The fracture of the alloy was brittle fracture.After the addition of Zr element,the crystal structure of Cu_0.3Cr₂Fe₂Ni₃Mn₂Zr_x?x=0.5,1.0?high entropy alloy was mainly consisted of FCC+BCC,which was well identified with the calculation results,Microstructure was a typical dendritic structure,and EDS spectrum showed that Zr element segregation in intergranular was more serious.With the increase of Zr content,the lattice distortion increased,and the content of BCC solid solution in the alloy increased and the FCC solid solution phase decreased.The hardness of the alloy was significantly improved,and was up to 600.34 HV.The alloy didnot not undergo plastic deformation during the stretching process,and brittle fracture occured at a small stress value.