Research On Brazing Of Tantalum Alloy Ta-2.5W And 0Cr18Ni9 Stainless Steel Plates

Tantalum is widely used in electronic,chemical industry,aerospace and other fields,due to the great advantages of high density,higher melting point,excellent corrosion resistance and good processability,but it is high in price.Tantalum-steel composite structure is commonly used in engineering,which can not only exert performance predominance of tantalum,but also reduce production costs.This paper design and prepare Zr-Ti-Cu-Ni and Ni-Cr-Fe-Si-B amorphous brazing fillers,aiming at the problem of the great differences of physical and chemical performances between tantalum and steel,which easy to produce brittle intermetallic compounds and lead to weld cracking.High-frequency induction brazing and vacuum furnace brazing were carried out on Ta-2.5W/0Cr18Ni9 and nickel-plated 0Cr18Ni9/Ta-2.5W with prepared amorphous brazing fillers based on the analysis of the brazing fillers' properties.The effects of brazing filler composition and brazing process on microstructure and properties of the joint were studied.The results show that:The solidus and liquidus temperatures of Zr45Ti30Cu15Ni10 amorphous filler are 824? and 835? respectively,and the molten temperature region is 11?.Under the conditions of welding current 15A,heating time 2s and holding time 13s,the shear strength of Ta-2.5W/Zr45Ti30Cu15Ni10/0Cr18Ni9 induction brazing joint is higher than 79.7MPa,and the fracture occurs at Ta-2.5W base metal near brazing seam.There is a partial oxidation on the base metal surface and brazing seam periphery forms a circular-arc fillet.The brazing seam is well bonded with base metal.The brazing seam is composed of(Fe,Cr)solid solution dendrite and Cr2Ta?Ni2Ta?Cr2Zr?Cu3Ti and a small amount of Fe5Ta3 compounds.The content of Fe element in the brazing seam decreased and the content of(Fe,Cr)solid solution reduced in the nickel-plated 0Cr18Ni9/Zr45Ti30Cu15Ni10/Ta-2.5W brazing joint.Under the same conditions,with the increase of holding time,the amount of 0Cr18Ni9 base metal dissolved in the brazing seam and the width of brazing seam increased.The solidus and liquidus temperatures of Ni82.5Cr7Fe3Si4.5B3 amorphous filler are 1002?and 1031? respectively,and the molten temperature region is 29?.Under the conditions of welding current 18A,heating time 3 s and holding time 13 s,the shear strength of Ta-2.5W/Ni82.5Cr7Fe3Si4.5B3/0Cr18Ni9 induction brazing joint is higher than 90.1MPa.The brazing seam and base metal are well combined,and the bonding interface is straight.The brazing seam microstructure consists of(Fe,Cr)solid solution,NiTa2,NiTa compounds and NiSi+NiSi2 eutectic.Under the condition of brazing temperature 1100?,holding time 5min and vacuum degree 5×10-2Pa,the brazing filler filled uniform and full in Ta-2.5W2Ni82.5Cr7Fe3Si4.5B3/0Cr18Ni9 furnace brazing joint.The central area of brazing seam is composed of Ni2Ta+NiSi?Ni2Ta+NiTa+NiSi+NiTa2 and NiSi+Ni3Si+NiTa,the transition zone between brazing seam and 0Cr18Ni9 is(Ni)solid solution,the transition zone between brazing seam and Ta-2.5W is NiTa+NiSi.The shear strength of the brazing joint is higher than 116.2MPa,and the fracture also occurs at Ta-2.5W base metal near brazing seam.The content of Fe?Cr elements decrease and diffusion distance become shorter in the brazing seam of nickel-plated 0Cr18Ni9/Ni82.5Cr7Fe3Si4.5B3/Ta-2.5W furnace brazing joint.Calculated by Fick's second law,in the process of Ta-2.5W/Ni82.5Cr7Fe3Si4.5B3/0Cr18Ni9 furnace brazing,the diffusion depth of Si element in 0Cr18Ni9 and Ta-2.5W are 50?m and 30?m respectively,the diffusion distance of B element in 0Cr18Ni9 and Ta-2.5W are 60?m and 4 ?m respectively.