Microstructure And Properties Of B₄C_p/Al Composites Prepared By Microwave Low Temperature Sintering

As the global economy continues to increase the demand for nuclear power energy,the development and improvement of spent fuel storage and application of high-performance neutron absorption shielding materials have become an urgent need.In this paper,20 vol.%B₄C_p/Al composites were prepared by microwave low temperature sintering method.Effects of milling and sintering parameters on microstructure and mechanical properties of B₄C_p/Al composites were discussed and optimized.The effects of TiB₂ addition amounts and original Al particle size on the microstructure and mechanical properties of?B₄C+TiB₂?_p/Al composites were investigated under the optimum preparation parameters.SEM,EDS,XRD diffraction analysis,nano-indentation,microhardness were used to characterize and analyze the microstructure and properties of the composites.The main results were as follows:?1?When the ball milling speed was 200 r/min and the time was 12 h,the welding and crushing of the B₄C/Al composite powder will achieve a dynamic balance continuously.The composite powder has high uniformity,uniform particles size and fine,and B₄C particles were uniformly embedded in the Al matrix.At this point,there are no other impurity peaks in the XRD diffraction pattern of the composite powder.The diffraction peaks were dominated by pure Al and a small amount of low and narrow B₄C particles,without the formation of B,C,and Al compounds.The compound powder keeps extremely high cleanliness before forming.?2?When the sintering temperature was 580?and the time was 45 min,the conversion efficiency of microwave in B₄C_p/Al composites was the highest,the resulting conpactness was 93.2%,and the hardness was 112.5 HV₁.The nano-hardness and elastic modulus at the interface were 7.494 GPa and 163.631 GPa,respectively.Under the condition of obvious temperature gradient in the unoptimized material,a certain amount of Al₃BC_?s?phase will be generated at the local interface as the second phase,which will strengthen it.However,when the Al₃BC_?s?phase was generated more,it would reduce the cleanliness and bonding strength of the interface between the reinforcing particles and the matrix.?3?TiB₂ ceramic particles were mostly distributed at the interface between B₄C particles and Al matrix,which reduces the sintering conditions of Al particles,fills some pores and inhibits the formation of Al₃BC_?s?phase,and has high interfacial cleanliness.when the amount of TiB₂ particles added was 2.5 vol.%,the microstructure of?B₄C+TiB₂?_p/Al composites was the best,the pores were few and narrow,and the interfacial bonding strength was high.At this time,the nano-hardness at the B₄C/Al interface was 9.235 GPa and the elastic modulus was 182.922 GPa.Compared with the B₄C_p/Al composites of the unadded TiB₂ particles under the same preparation parameters,the nano-hardness and elastic modulus at the interface were increased by23.2%and 11.8%respectively.The microhardness of the composites was relatively high,the highest compactness was 94.6%.When the addition amount of TiB₂ particles exceeds 2.5vol.%,the pores in the composites increase and the B₄C particles showed uneven distribution.?4?When the size of the original Al matrix particles added was too small,the formation of interfacial pores was large,the matrix particles easily formed large-sized aggregates,and the reinforcement particles were difficult to achieve uniform distribution in the?B₄C+TiB₂?_p/Al composites.When the size of the original Al matrix particles added was 2?m,the reinforcement particles were more evenly distributed in the Al matrix.At this time,the compactness of the composites was relatively high,and the microhardness was up to 188.6 HV₁.When the size of the original Al matrix particles added was larger,the plastic deformation was smaller,the crushing was incomplete,and the particles were difficult to be fully refined,resulting in an uneven distribution of the reinforcement.There is even agglomeration of reinforcement in some areas,stress concentration,micro-cracks and reduced compactness.