Strengthening mechanism of nickel foam interlayer on vacuum brazing joint of B4C ceramics and TC4
During vacuum brazing B4C ceramics and TC4 titanium alloy,there is a great difference in the thermal expansion performance between them,which is easy to crack due to excessive residual stress.In this paper,vacuum brazing of B4C ceramic and TC4 titanium alloy without cracking defect was successfully achieved by adding nickel foam interlayer.The microstructure of brazing joint was observed,and the residual stress and elastic strain energy of joint were calculated and analyzed.The results show that the shear strength of vacuum brazed joint is 88.6 MPa.The addition of nickel foam interlayer can effectively relieve the excessive dissolution of B4C by active Ti element,reduce the formation of brittle compounds,such as TiC and TiB2,and promote the uniform distribution of brazed filler metal composition.On the other hand,the softened and collapsed nickel foam skeleton structure divides the molten filler metal,resulting in a number of small fusion zones,so that the force of the weld structure is more uniform,and the residual stress is also relieved to a certain extent,which is conducive to the formation of a good connection between B4C ceramics and TC4 titanium alloy.B4C ceramic and TC4 titanium alloy achieves stress relief after the addition of nickel foam interlayer,which further verifies that the ceramic/metal dissimilar material connection can be stress release through porous materials.
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