Microstructure and residual stresses of brazed graphite tubes and stainless steel tubes
In order to fully utilize the potential of graphite materials in space nuclear power heat sinks,the joining of graphite tube and 304 stainless steel tube have been prepared by brazing with BNi-2 filler material in a vacuum at 1 010℃ for 90 min.Microstructure and the effect of different cooling processes on the residual stresses of graphite/BNi-2/stainless steel joints under this process were investigated.The experimental results illustrate that under the condition of 1 010 ℃ and 90 minutes of insulation,the brazed joints exhibit a dense and crack-free structure.Moreover,part of Cr reacted with the graphite matrix to form Cr7C3 reaction layer in the graphite side,while a σ-FeCr diffusion layer was formed on the stainless steel side.The interface microstructure of the brazed joints was graphite/Cr7C3/Ni(s,s)+Ni3Si/σ-FeCr/stainless steel.Additionally,the room temperature shear strength of the joint treated by the temperature-controlled cooling process was 28.38 MPa,which was 22％higher than that of the furnace-cooled joint.The finite element numerical analysis results showed that the residual stresses generated during the cooling of brazed joints were effectively relieved when the temperature-controlled cooling process was used,which is in consistent with the shear test results.
nickel-based brazing alloygraphite tubestainless steel tubemechanical propertiesfinite element numerical analysisbrazing
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