Microstructure And Properties Of New Gd Riched Ni-based Alloys

Neutron absorbing materials are the key functional materials in the field of spent fuel storage and transportation.In order to remove the constraints of the development of nuclear power in China,it is of great theoretical and practical significance to develop and design neutron absorbing materials with integrated structure and function.Three new Gd-riched Ni-based alloys have been developed according to the requirements of shielding materials in the field of spent fuel storage and transportation.The results show that the mechanical properties,corrosion resistance and welding properties of the new Gd-riched Ni-based alloy can meet the structural use requirements for materials in the field of spent fuel storage and transportation,and the alloy has excellent thermal neutron absorption performance can also meet the requirement of neutron absorption performance of spent fuel materials.The main conclusions are as follows:(1)The addition of Gd can promote the formation of Gd intermetallics are hexagonal crystal structure in the alloy.The precipitated phase in the alloy Ni-30Cr-(10-x)Fe-xGd,Ni-30Cr-5Fe-5Mo-xGd(x=0.5,1.0,1.5,2.0,3.0 wt.%)is(Ni,Cr,Fe)5Gd,and is(Ni,Cr)5Gd in Ni-30Cr-xGd(x=0.5,1.0,1.5,2.0,3.0 wt.%)alloy.Gadolinium intermetallics are precipitated at 1280±15℃.The number of Gd intermetallics which were mainly distributed along the grain boundary of austenite are increased with the increase of Gd content.(2)The addition of Gd can significantly improve the hardness of the alloy and reduce the tensile strength and fracture elongation at room temperature in the new Gd-riched Ni-based alloy.The addition of Mo can improve the hardness and tensile strength of the alloy,and reduce the fracture elongation of the Ni-30Cr-5Fe-5Mo-xGd alloys.By comparing the properties of Ni-30Cr-xGd and Ni-30Cr-(10-x)Fe-xGd alloys,it was found that the addition of Fe reduced the melting point and precipitation temperature of the alloy,and decreased the hardness and tensile strength of Gd-riched Ni-based alloy.When Gd content is low,the alloy is mainly transgranular fracture,while when Gd content is high,the fracture mode of the alloy is transgranular fracture+intergranular fracture.(3)The corrosion behavior of the alloy shows that the precipitated phase Gd intermetallics in the alloy will be the first to be corroded,and the increase of Gd can reduce the corrosion resistance of the Gd-riched Ni-based alloy in the simulated wet storage environment of spent fuel.The experimental results show that the new Gd-riched Ni-based alloy has excellent corrosion resistance and low corrosion rate in boric acid.(4)The new Gd-riched Ni-based alloy has good welding performance and can realize autogenous welding without adding filler metal by vacuum electron beam welding and argon tungsten-arc welding.The new Gd-riched Ni-based alloy has good welds performance and the vauum electron beam welds are better than TIG welds.(5)The absorption performance of the new Gd-riched Ni-based alloy for thermal neutron is mainly determined by the content of Gd and material thickness.The decrease of neutron transmissivity is more influenced by the increase of alloy thickness than by the increase of Gd content.With the same Gd content and thickness,the thermal neutron absorption of Ni-30Cr-xGd alloy is best.The thermal neutron transmissivity of the new Gd-riched Ni-based alloy is lower than 304-0.5B,304-1.2B and lead-boron polyethylene of the same thickness.The new Gd-riched Ni-based alloy has excellent tensile mechanical properties at room temperature,corrosion resistance and weldability,etc.It can meet the requirement of thermal neutron absorption of spent-fuel storage and transport materials.It is a waste fuel storage and transportation material with integrated structure and function.