Aluminium magnesium boride

It is a ceramic alloy that is highly resistive to wear and has an extremely low coefficient of sliding friction, reaching a record value of 0.04 in unlubricated[4] and 0.02 in lubricated AlMgB14−TiB2 composites.

BAM powders are commercially produced by heating a nearly stoichiometric mixture of elemental boron (low grade because it contains magnesium) and aluminium for a few hours at a temperature in the range 900 °C to 1500 °C.

[5][6] To ease the reaction and make the product more homogeneous, the starting mixture can be processed in a high-energy ball mill.

[10] BAM usually contains small amounts of impurity elements (e.g., oxygen and iron) that enter the material during preparation.

It is thought that the presence of iron (most often introduced as wear debris from mill vials and media) serves as a sintering aid.

[4] Most superhard materials have simple, high-symmetry crystal structures, e.g., diamond cubic or zinc blende.

The occupancy of metal sites in the lattice is lower than one, and thus, while the material is usually identified with the formula AlMgB14, its chemical composition is closer to Al0.75Mg0.75B14.

This property originates from electron transfer from metal atoms to the boron icosahedra and is favorable for thermoelectric applications.

[7][8] A composite of BAM and TiB2 (70 volume percent of TiB2) has one of the lowest values of friction coefficients, which amounts to 0.04–0.05 in dry scratching by a diamond tip[9] (cf.