Self-Propagating High-Temperature Synthesis of Boron-Containing MAX-Phase

Abstract

An attempt was made to obtain boron-containing MAX-phase by the process of self-propagating high-temperature synthesis (SHS) of Ti3AlC2, replacing some carbon atoms by boron atoms. This was conducted by burning powder mixtures (charges) of the composition 3Ti+2Al+2((1-x)C+xB), where x is the fraction of boron atoms (0.10, 0.15, 0.25, 0.50, 0.75, 0.90), replacing the carbon atoms. X-ray diffraction analysis of the products of combustion have shown that the replacement of carbon with boron to half of the content of carbon atoms in the charge (x=0.10-0.50), does not change the phase composition of the products, including Ti3AlC2 and TiC, but leads to a shift of the peaks of these phases in the diffraction pattern in the direction of smaller angles. When replacing more than half of the carbon atoms with the boron (x=0.75 and 0.90), the peaks of titanium carbide and MAX-phase are not observed, and the XRD peaks appear of the titanium borides TiB and TiB2, and intermetallic compound Al3Ti. Photomicrographs obtained with an electron microscope show that the SHS products synthesized from the charge with replacing up to half of the carbon atoms with the boron represent plates with a thickness of about 1 μm typical for MAX-phases, but rounded particles of borides and intermetallic compound of titanium appear at a higher boron content. Based on these results, it is concluded that replacement of a part (up to 50%) of the carbon atoms with boron atoms in the SHS charge 3Ti+2Al+2C leads to the synthesis of boron-containing MAX-phase based on the crystal lattice of Ti3AlC2.