| The new concept of high-entropy alloy(HEA)has attracted wide attention since its birth.HEAs usually contain five or more major elements,and the content of each element is between 5%and 35%by atom ratio.The unique composition of HEA makes it has excellent high strength,high hardness,corrosion resistance and excellent high temperature and low temperature mechanical properties by changing the composition and proportion of the alloy.The most common preparation method of high entropy alloy is casting.However,due to the composition segregation and other problems,it is difficult to manufacture bulk alloys,and the later processing is difficult,which restricts the application of high entropy alloys Wire arc additive manufacturing(WAAM)has the advantages of high deposition efficiency,high material utilization rate,large size of manufacturing parts and low equipment cost,which has attracted more and more attention of scholars and industry.In this experiment,combined cable wire(CCW)was used for arc additive manufacturing,and non-equimolar Al-Co-Cr-Fe-Ni HEA was prepared.The influence of process parameters of CCW-AAM on the forming of HEA was systematically studied,which laid a foundation for the preparation of HEA parts and provided a new idea for additive manufacturing of HEAs.In addition,the effect of heat treatment temperature on the microstructure and mechanical properties of the alloy was studied.(1)By changing the wire feeding speed and the travel speed of welding torch,the forming process window of CCW-AAM and the forming law of single pass weld were studied.With the increase of wire feeding speed,the width of weld increases gradually,the height remains unchanged,and the cross-sectional area increases;with the increase of welding torch running speed,the width,height and cross-sectional area of welding seam decrease.The optimal process range is wire feeding speed of 5.5 m/min and welding torch travel speed is 8-12 mm/s.In this region,the weld is closely connected with the basic part,the weld is well formed and the surface quality is the best.(2)The effect of heat input(by changing torch travel speed)on microstructure and mechanical properties of Al-Co-Cr-Fe-Ni HEA was studied.The results show that the alloy consists of BCC and FCC phases,which are 67.33%and 32.67%respectively.With less heat input,the grain size of the alloy sample is smaller(about 10 ?m)and much smaller than casting sample(about 30 ?m).In addition,the lower the heat input,the better the mechanical properties of HEA sample.The yield strength is 816 MPa,the ultimate compressive strength is 2835 MPa and the plastic strain is 41.79%when the welding torch travel speed is 12 mm/s.Compared with the casting sample,the ultimate compressive strength and plastic strain of the CCW-AAM samples increased by 4.1%and 11.7%,respectively.(3)The effect of heat treatment temperature on microstructure and mechanical properties of Al-Co-Cr-Fe-Ni HEA was studied.After heat treatment at 600?,Cr-rich ? phase is precipitated in BCC phase matrix of the HEA sample.The hardness and yield strength of the alloy are increased by 24.5%and 20%respectively,but the plasticity is greatly reduced.After heat treatment at 800?,the growth of ? phase in BCC matrix weakens the precipitation strengthening effect.In addition,the rod-like BCC phase precipitates in FCC matrix,which results in precipitation strengthening,but weakens the solid solution strengthening.The mechanical properties are better than as-deposited sample.The alloy with the best mechanical properties can be obtained by this process.After heat treatment at 1000?,? phase is redissolved in BCC matrix,only a small amount of ? phase still appears at the grain boundary.The growth of rod-like BCC phase in FCC matrix further weakens the solid solution strengthening effect of FCC phase.At this temperature,the HEA can be softened well,which makes it have good ductility. |
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