Compatibility Study Of B₄C Neutron Absorber Based On Al-Si Eutectic Alloy

Because of lower neutron absorbing ability,higher heat transmit coefficient, and better anticorrosion,Al-Si eutectic alloy may be an ideal base material for B₄C neutron absorber.The compatibility between Al-Si eutectic alloy and B₄C,or canister materials,such as 1Cr18Ni9Ti stainless steel and Zirconium alloy,directly influence the absorbing ability and operational life,so it is necessary to investigate them.Based on the preparation of high density block of B₄C dispreading on Al-Si eutectic alloy,the compatibility of Al-Si eutectic alloy with B₄C,with 1Cr18Ni9 Ti stainless steel,and with Zirconium alloy have been investigated separately.The diffusion couples of Al-Si & 1Cr18Ni9Ti,Al-Si & Zr,and Al-Si & B₄C were prepared by powder-metallurgy method.Then these couples were heated to different temperature for different time.The compatibility and diffusion layer under different heat treatment conditions were measured by SEM,EDS,XRD.The diffusion mechanism at 350℃,560℃and 650℃were discussed.It was shown that the compatibility between them is greatly determined by diffusion temperature.At 350℃for 240h,Al-Si entectic alloy has a good compatibility with B₄C,stainless steel and Zirconium alloy.There are no significant reaction and diffusiion between components.Isothermally treated 240h at 560℃,there is a solid state reaction between Al-Si & 1Cr18Ni9Ti,Al-Si & Zr, but the diffusion layer is very thiner,which means a good compatibility between them.Because of no reaction isothermally treated for 240h,there is a very good compatibility between Al-Si and B₄C.Heated to 650℃,aluminium become to liquid,the dramatic diffusion layer has formed between Al-Si & 1Cr18Ni9Ti,due to infiltration and diffusion reaction.The Fe₂Al₅ has been found in the diffusion layer,which means a bad compatibility between them.So as to Zirconium alloy, the Zr₃Al has been found in diffusion layer of Al-Si & Zr at 650℃.For Al-Si & B₄C,a very good compatibility has displayed,due to no reaction between them.For solid diffusion,the diffusion layer thickness increases slowly with isothermal time.At 560℃,the 5～8μm diffusion layer of Al-Si & 1Cr18Ni9Ti for 48h has formed.The thickness of diffusion layer for 24oh increases to 15～20μm. The effects of temperature on growth of diffision layer and diffusion velocity are greater than isothermal time.For same 240h,the diffusion couple forms a thicker diffusion layer at 560℃,but no diffusion layer at 350℃.It is shown that under the normal used temperature 300℃,the diffusion couples of Al-Si & 1Cr18Ni9Ti,Al-Si & Zr,and Al-Si & B₄C all have a good compatibility,which means that they can meet the requirements of normal operation.