Solid-state reaction in mechanically milled and spark plasma sintered Al–B4C composite materials

Air-atomised pure aluminium powder with additions of 12.5 at%, 37.5 at% and 62.5 at% of B4C was mechanically alloyed (MAed) by using a vibrational ball mill, and MAed powders were consolidated into bulk materials by a spark plasma sintering (SPS) process. Solid-state reactions of the MAed powders during heat treatments were examined by X-ray diffraction (XRD), and mechanical properties of the MAed powder obtained under various heat treatment conditions and those of the SPS materials were evaluated by hardness tests. The solid-state reactions occurred among pure aluminium, B4C and stearic acid, added as a process control agent (PCA), after heating at 673 K to 873 K for 24 h to form AlB10, Al3BC and γ-Al2O3. The products obtained by solid-state reactions have affected the Vickers microhardness of the heat-treated MAed powders. The near full density was obtained for the SPS materials under the conditions of an applied pressure of 49 MPa at 873 K for 1 h. The Al–12.5B4C SPS material from 16 h MAed powder exhibited the highest hardness value of 210 HV in the as-fabricated state.