| The structure of tantalum-steel composite is widely used in electronic,chemical industry,aerospace and other fields,due to comprehensive performance of tantalum and steel.The serious problem including the great differences in physical and chemical performances between tantalum and steel is easy to produce brittle intermetallic compounds and lead to weld cracking.In this paper,capacitor discharge welding(CDW)with rapidly solidified of Tal and 0Cr18Ni9 sheets was carried.Ta-Ni-Cr-V,Ta-Ni-Cr-Cu and Ta-Ni-Cr-Co three interlayer alloys were designed and prepared according to the principle of nugget metal high entropy.The compositions of three interlayer alloys for Tal/0Cr18Ni9 CDW were optimized by means of the orthogonal experiment.The joints of Tal/0Cr18Ni9 direct CDW and based on interlayer alloys Ta1/0Cr18Ni9 CDW were carried out.And the phase composition and microstructure of the joints were analyzed.The influence rules of welding process on properties of the joints were studied.The results are summarized as following:The excellent plasticity of three nugget metal are Ta22.22Fe22.22Ni22.22Cr22.22V11.11,Ta20Fe20Ni20Cr20Cu20 and Ta20Fe20Ni20Cr20Co20 respectively by the density-functional theory calculation.According to the penetration ratios of base material in nugget and orthogonal testing optimum design methodology,the compositions of multicomponent interlayer alloys for Tal/0Cr18Ni9 CDW are Ta13Ni35Cr28V24,Ta8Ni30Cr20Cu42 and Ta7Ni32Cr19Co42 in turn.Three alloys have great liquidity and liquid formation.Interlayer alloys foils are obtained by rapidly quenched solidification and their size are about 80 to 100 micrometers thick,8 to 10 millimeters in width and about 100 millimeters long.CDW can realize the weld of Tal/0Cr18Ni9 and effectively inhibit brittle intermetallic compounds in some extent.However,a small amount Fe5Ta3 and Cr2Ta intermetallic compounds are produced in nugget center.The subcircular porosity in diameter about 0.2mm appeared in nugget and micro-shrinkage appeared at the interface between tantalum and steel.The whole nugget shifted to the 0Cr18Ni9 steel.The joints have the lowest strength and average on about 240MPa.Under the condition of welding voltage U=1000V,capacitance C=500?F,electrode force F=30N,three interlayer alloys are used for Tal/0Cr18Ni9 CDW based on nugget metal high entropy alloyed.The joints have a good formation without weld defects such as porosities.All of nuggets shifted to the 0Cr18Ni9 steel and bonding zone between nugget and base metal is good.The phase composition of nugget is composed of simple cubic instead of intermetallic compounds,so the strength of joints are improved.The shear strength of joints with interlayer alloys are higher than welded joints without interlayer.The microstructure of Tal/Ta13Ni35Cr28V24/0Cr18Ni9 CDW bonding zone between nugget and base metal is made up of columnar crystals and the microstructure of molten core is composed of columnar,coarse dendrites and a little equiaxed crystals.The shear strength of the joint is up to 372MPa.The microstructure of Tal/Ta8Ni30Cr20Cu42/0Cr18Ni9 CDW nugget is composed of coarse dendrites and equiaxed crystals.The shrinkage cavities uneven distributed are produced at the interface between tantalum and nugget.Average shear strength of the joint is up to 362MPa.The joint of Tal/Ta7Ni32Cr19Co42/0Cr18Ni9 CDW nugget is composed of cellular crystal,which is neatly arranged at the interface between tantalum and steel.The microstructure of nugget core is made up of dendrites and a little equiaxed crystals.Average shear strength of the joint is up to 395MPa.The shear strength of CDW joint with Ta7Ni32Cr19Co42 interlayer alloy is the highest,the following reasons:the joint without weld defects,the FCC structure of nugget,the tensile shear fracture with a large number of dimples and no brittle intermetallic compound. |
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