Properties of mechanically milled and spark plasma sintered Al–AlB 2 and Al–MgB 2 nano-composite materials

Abstract

Air-atomized pure aluminium powder was mechanically alloyed (MA) with AlB 2 or MgB 2 by using a vibrational ball mill, and MA powders were consolidated by spark plasma sintering (SPS). Solid-state reactions of MA powders have been examined by X-ray diffraction (XRD), and mechanical properties of the SPS materials have been evaluated by hardness measurements and compression tests. The solid-state reactions in both Al–AlB 2 and Al–MgB 2 composites occurred between the MA powders and stearic acid used as a process control agent after heating at 573–873 K for 24 h. Formation of Al 3BC ternary compound occurred in both composites. Formation of γ-Al 2O 3 was observed in the Al–AlB 2 whereas formation of MgAl 2O 4 occurred in the Al–MgB 2. As the result of solid-state reactions in both composites, a hardness increase was observed in MA powders after heating at 573–873 K for 24 h. The full density was attained for the SPS materials from 4 h MA or 8 h MA powders in both composites under an applied pressure of 49 MPa at 873 K for 1 h. The compressive proof strength of the SPS material of the Al–MgB 2 was higher than that of the Al–AlB 2. The SPS material of Al 85(MgB 2) 15 from 8 h MA powder exhibited the highest compressive proof strength of 846 MPa at room temperature.