| High entropy alloys(HEAs)exhibit excellent mechanical properties over a wide temperature range,demonstrating their structural stability.These properties make them suitable as structural materials for use in nuclear and aerospace applications.Given the need for dissimilar joint design in these applications,this study explores the weldability of CoCrFeMnNiHEA and 304 stainless steel.CoCrFeMnNiHEA self-fusion welding joints were first prepared using gas tungsten arc welding(GTAW).Then,CoCrFeMnNiHEA/304 stainless steel dissimilar joints were prepared.In addition,CoCrNiMEA,a derivative of CoCrFeMnNialloy,has similar radiation resistance and superior mechanical properties to CoCrFeMnNiHEA.Thus,the welding of CoCrNiMEA/304 stainless steel dissimilar joints was further investigated.The microstructure,mechanical properties,and corrosion resistance of the three joints were characterized,and relevant mechanisms were analyzed.The specific research results are as follows:No welding defects were found in the CoCrFeMnNiHEA self-fusion welding joint,and no intermetallic phase was generated during the welding process.The microstructure exhibited gradual growth from large columnar grains near the fusion line to equiaxed grains toward the centerline.Mechanical property tests showed that the hardness of the fusion zone was lower than that of the base material,but the tensile strength of the joint was equivalent to that of the base material,and the joint fracture occurred on the unaffected base material,indicating that the welding joint is safe for use in engineering structures.However,element segregation in the fusion zone resulted in the formation of an uneven and unstable passive film on the surface,leading to a decrease in the joint’s corrosion resistance.The CoCrFeMnNiHEA/304 stainless steel dissimilar joint was well fused,with no apparent defects and good weldability.Due to the relatively low liquid phase temperature of the weld metal compared to the base material,the composition was too cold,resulting in an unmixed zone(UZ)near the 304 stainless steel side.The microhardness of the dissimilar joint exhibited an asymmetric distribution,with the UZ being the highest.At the same time,the joint’s hardness in the fusion zone was higher than that of CoCrFeMnNiHEA due to the combined effects of grain refinement and C element strengthening.It is worth noting that the joint obtained a tensile strength equivalent to that of HEA,and it fractured on the CoCrFeMnNiHEA side,indicating that the joint meets the requirements for room temperature structural applications.In addition,the welding joint exhibited corrosion resistance comparable to that of the base material.The CoCrNiMEA/304 stainless steel dissimilar joint was intact without any apparent defects,with uniform element distribution and no intermetallic phase.The hardness of the fusion zone decreased,but the yield strength increased by 12% compared to that of CoCrNiMEA.The ultimate tensile strength was equivalent to that of CoCrNiMEA.However,joint failure occurred in the fusion zone,which is not conducive to its application in structural components.Corrosion resistance tests showed that the joint’s corrosion resistance did not decrease significantly compared to that of the base material. |
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