Mechanochemical synthesis of chromium borides

Abstract

Chromium and boron compounds have potential for structural applications which require high temperature strength because of their high melting point, chemical stability, hardness and strength. Ball-milling of elemental powder mixtures without external heat application has been processed as a mechanism for the mechanochemical synthesis of high melting point compounds. Chromium and amorphous boron elemental powder mixtures at atomic ratios of 1 : 1 and 1 : 2 were processed for 10-40h in a planetary ball-mill. CrB2 was formed at a low yield after 10-30h of milling the 1 : 2 mixture using tungsten carbide balls. However, a single phase of CrB2 was found by XRD, after the as-milled Cr-B (1: 2) mixture was annealed at 900°C for 2h. A single phase of CrB was formed by annealing the Cr-B (1:1) mixture at 1000°C for 2h. Ball-milling of the elemental powder mixtures before annealing significantly reduced the reaction temperature necessary for chromium boride synthesis. The as-milled Cr-B (1 : 2) mixture contained fewer contaminations (tungsten and cobalt) than the as milled Cr-B (1 : 1) mixture. The lattice parameters of the chromium borides obtained agree with previously reported measurements.