Synthesis of Al 3BC from mechanically milled and spark plasma sintered Al–MgB 2 composite materials

Abstract

The aluminium-rich ternary aluminium borocarbide, Al 3BC was synthesised for the first time by solid-state reactions occurring during heat treatments after mechanical milling (MM) of pure aluminium with 15 or 50 at% MgB 2 powder mixtures in the presence of the process control agent (PCA). The solid-state reactions in the Al–15 and 50 at% MgB 2 composite materials occurred between the MMed powders and process control agent (PCA) after heating at 773–873 K for 24 h. The products of the solid-state reaction induced Al 3BC, AlB 2, γ-Al 2O 3 and spinel MgAl 2O 4. MM processing time and heating temperatures in the Al–15 and 50 at% MgB 2 composite materials affected the selection of those intermetallic compounds. When MM processing time was increased for a given composition, the formation of the Al 3BC compound started at lower heat treatment temperatures. However, when the amount of MgB 2 was increased in the 4 h MM processing regime, the formation of the Al 3BC compound during heating was suppressed. As a result of the solid-state reactions in MMed powders the hardness was observed to increase after heating at 573–873 K for 24 h. The fully dense bulk nano-composite materials have been successfully obtained through the combination of the MM and spark plasma sintering (SPS) processes for the 4 h or 8 h MMed powders of the Al–15 at% MgB 2 composite materials sintered under an applied pressure of 49 MPa at 873 K for 1 h.