Research On The Fabrication Of Al-B₄C-Al₂O₃ Composites By Liquid Process And Solid-state Distribution Technology

With the rapid development of nuclear power in the whole world,the amount of spent fuel produced by nuclear power plants booms.Known as neutron absorber structure-functional materials,Al-B₄C-Al₂O₃ composites possess outstanding mechanical properties,good capacity for neutron absorption and heat conduction,being an ideal choice to accomplish the high-density storage of spent fuel.Liquid-state process,with a relatively simple craft and no limitation to the size and shape of casting billet,has already been applied in the fabrication of Al-B₄C neutron absorber materials.But it is still difficult for the introduction and distribution of nanoparticles in the fabrication of Al-B₄C-Al₂O₃ composites through liquid process.So,aimed to investigate a set of preparation craft to introduce and disperse nanoparticles effectively in the Al-B₄C-Al₂O₃ composites,this thesis bases on liquid state process and hot processing,and systematic researches on nanoparticle introduction technology,ultrasonic assist dispersion technology and two kinds of solid state dispersion technologies of equal channel angular pressing and hot rolling are carried out respectively.Based on liquid state process,a large-sized Al-B₄C-Al₂O₃ composite plate is fabricated successfully by introducing Al₂O₃/Al mixed powder into Al-B₄C composite melt.In the ball milling process of Al₂O₃/Al mixed powder,micro-Al spherical particles are milled to small twisted and crimpled foils and Al₂O₃particles embedded on it,with the mass ratio of Al₂O₃/Al being 5:5.Employing larger balls of 10mm from 6mm,twisted and crimpled Al foils are compressed to shuttles,with the Al₂O₃ particles on it.And Al-B₄C-Al₂O₃ composite performs better than Al-B₄C composite with strengthened mechanical properties at room temperature and high temperature.High intensity ultrasonic is introduced into the Al-B₄C-Al₂O₃ composite melt,and the distribution homogeneity of Al₂O₃ particles and mechanical properties of the materials at room temperature and high temperature are improved.When applying high density ultrasonic to 15 minutes,flocculent TiB₂is observed in matrix,with improved distribution homogeneity of Al₂O₃particles.When the ultrasonic time is to 30 minutes,B₄C particles are eroded by the aluminum melt severely,and the amount of flocculent TiB ₂ decreases.The tensile properties of Al-B₄C-Al₂O₃ composites with 15 minutes processing is better than that with 30 minutes processing,with ultimate tensile strength improving 18%at room temperature and 25%at 350 degrees.And with two kinds of solid state dispersion processing of equal channel angular pressing and hot rolling,the distribution homogeneity of particles in the matrix is improved further,and the defects in the matrix are removed to a large extent.With 4 passes of equal channel angular pressing,B₄C particles rotate an angle relative to the matrix and Al₂O₃ particles around it remove in different directions and make redistribution in the matrix.When it comes to rolling with a reduction of 30%,partial particle agglomeration of B ₄C disappears,with particle orientation turning to the rolling direction,and the density and elongation of Al-B₄C-Al₂O₃ composites reach to the best,being 98.15%and10.6%respectively.