Microstructure and mechanical properties of (B_4C+Al_2O_3)/Al composites designed for neutron absorbing materials with both structural and functional usages

摘要

To meet the demand for the new generation of neutron absorber materials (NAMs) for the dry storage of the spent nuclear fuels, (B_4C + Al_2O_3)/Al composites were fabricated by powder metallurgy technique using ul-trafine Al powders. The composites designed with various fabricating parameters and fabricated at various sintering temperatures were characterized by electron microscopy and mechanically tested. The sample sintered at 450 ℃ shows the best strength-ductility balance at 350 ℃ (106.2 MPa in ultimate tensile strength and 9.6% in elongation). Addition of B_4C particles and increase of the Al_2O_3 film thickness could enhance the strength of the composites at room temperature but showed no obvious effect on the strength at 350 ℃. When sintering temperature of the composites increased from 450 ℃ to 550 ℃, the transformation of amorphous Al_2O_3 lamellae to γ-Al_2O_3 particles led to deterioration of the strength of the composites. Based on the analyses of both high-temperature deformation mechanism and strengthening mechanism, it was considered that the amorphous Al_2O_3 could pin the grain boundaries and prevent them from gliding, which was the main factor to significantly increase the high-temperature strength. Based on the results, a strategy to design the aluminium matrix NAMs with excellent high-temperature strength was proposed.