Study On Preparation,Microstructure And Properties Of (W+B)/Al Composites

With the service of new nuclear reactors and movable reactors,the requirements for the radiation shielding materials'properties have changed from single neutron radiation shielding to neutron and?-ray radiation shielding.At present,the radiation shielding materials,such as boron steel and lead-boron polyethylene,are unable to meet the requirements of application due to the limitation of their single shielding property and low structural strength.In order to solve these problems,tungsten?W?and boron?B?are used as?-ray and neutron shielding components,respectively,and they are added into aluminum alloy matrix to prepare Al-based radiation shielding composites.In this paper,W and B single particles are chosen as shielding absorption component and 6061Al alloy as matrix material.First,the radiation shielding performance of composite materials was simulated by MCNP program.The W content in the material is determined to be 40 to 55 wt.%and the content of B is1 wt.%.Then the composite billets were prepared by spark plasma sintering?SPS?.Finally,?W+B?/Al composites were prepared by hot rolling.Microstructure of?W+B?/Al composites and binding mechanism of the interface between particles and matrix were analyzed.The strengthening mechanism of the reinforced particles on the matrix and the fracture mechanism of the materials were studied.The corrosion resistance and corrosion mechanism of rolled?W+B?/Al composites were studied by electrochemical corrosion tests.The main findings are as follows:The relationship between shielding component content and material thickness and neutron shielding performance of?W+B?/Al composites was first established by Monte Carlo method and MCNP program simulation.The constitutive relation between the thickness and neutron transmittance of composites with different W content is obtained.Secondly,the linear attenuation coefficient and half-value layer thickness of?W+B?/Al composites under ¹³⁷Cs and ⁶⁰Co-?-ray sources were calculated by simulation.The?W+B?/Al composites containing 40⁵5 wt.%W and 1 wt.%B were prepared by high-energy ball milling+SPS method.The distribution uniformity of the particles?W,B?in the composites prepared by SPS decreased gradually with the increase of their content,and the agglomeration of the particles resulted in the decrease of the density of the composites.The main phases of the composites are W and Al,with a small amount of B and WAl₁₂,AlB₁₂,and W₂B.In addition,the formation process of W-Al interface includes two stages:W+Al?WAl_4?5?and WAl_4?5?+Al?WAl₁₂.The densification of?W+B?/Al composites increased obviously after hot rolling and the interfacial bonding between particles and matrix is improved.The existence of reinforced particles promotes the dynamic recrystallization nucleation of the matrix and significantly inhibits the grain growth of the matrix and reduces the texture phenomenon of the aluminum alloy matrix.The tensile strength of composites can reach up to 195.5 MPa,which increased by 55%compared with Al alloy matrix.The fracture mechanism of the material is mainly the debonding of the interface between the reinforced particle and the matrix and the cleavage fracture of the W particle itself.The strengthening mechanisms of the composites include load transfer strengthening,dislocation strengthening caused by thermal mismatch and fine grain strengthening.The electrochemical corrosion test shows that the corrosion resistance of composites decreases with the increase of particle content.The electrochemical corrosion process of composite is mainly galvanic corrosion.The existence of galvanic corrosion will accelerate the corrosion of Al alloy matrix.