Microstructure And Properties Of TLP Welded And Brazed Joints Of CoCrFeMnNi High Entropy Alloy And 304 Stainless Steel

In this paper,the BNi-2 interlayer and Ag/Cu(50Ag-50 Cu,at.%)solder were used to carry out TLP welding and brazing of CoCrFeMnNi high entropy alloy and 304 stainless steel respectively.The effects of welding temperature,heat preservation time and thickness of solder on the microstructure and properties of welded joints were investigated by scanning electron microscopy(SEM),EDS,tensile test and microhardness test.The possibility of connection between CoCrFeMnNi high entropy alloy and 304 stainless steel was explored.The experimental results of CoCrFeMnNi and 304 stainless steel TLP welding show that:(1)The metallurgical bonding between CoCrFeMnNi high entropy alloy and 304 stainless steel is realized by using BNi-2 interlayer at 950~1150? for 60 min.The best welding process is 1050? for 60 min,and its tensile strength can reach 573 MPa.(2)The B in the BNi-2 interlayer reacted with CoCrFeMnNi high entropy alloy and 304 stainless steel in the interlayer and form particles and dendritic boride in the welding interface near the base alloy.These boride existed in the intergranular and intragranular positions,and limited the excessive growth of the matrix metal at high temperature.(3)The composition of the welded joint is composed of CoCrFeMnNi high entropy alloy /DAZ(solid solution layer / dendritic tissue layer / particles tissue layer)/ISZ(rich-Ni solid solution)/DAZ(particles tissue layer / dendrite layer / solid solution layer)/304 stainless steel in the temperature range of 950~1050?,and the composition of the welded joint at 1100? and 1150? it is composed of CoCrFeMnNi high entropy alloy /DAZ(solid solution layer / dendrite layer)/ISZ(rich-Ni solid solution)/DAZ(dendrite layer / solid solution layer)/304 stainless steel.The change of the microstructure of the joint is caused by the different diffusivity of B atoms at different temperatures.The experimental results of brazing CoCrFeMnNi and 304 stainless steel show that:(1)A characteristic tissue of CoCrFeMnNi high entropy alloy and 304 stainless steel are welded with Ag/Cu(50Ag-50 Cu,at%)brazing solder is peak like or cobblestone like Cu based solid solution and striations Ag-Cu eutectic structure,and a mixture of white rich-Ag solid solution,gray rich-Cu solid solution and black CoCrFeMnNi in the side of high entropy alloy matrix near the welding interface.(2)In the range of 790~880 C welding temperature,the microstructure and properties of the joint have a great change.The microstructure and properties of the joint are basically the same in the range of 1 ~ 10 min,and the microstructure and properties of the joint are basically the same in the range of 0.03 ~ 0.15 mm of the thickness of the solder.(3)Mn has a higher diffusion rate under the experimental conditions of brazing.It has more content in the weld.