Innovative MAB phase-based MoAlB ceramics produced by forced SHS pressing technology

Abstract

Compact ceramic materials based on the following MAB phase: MoAlB, were obtained using the forced SHS pressing technology. The authors looked at the effect of excessive aluminium on the combustion parameters of the mixtures in view, as well as on the phase composition and structure of the synthesized samples. It was found that the high residual porosity of the samples is associated with a decreased filtration capacity of the gases released in the combustion wave due to their locking in the reaction mixture briquette by layers of the “chemical oven” located on both sides of the briquette. As a result of SHS pressing technology optimization, ceramic material with a porosity of 9.6% and a 97% concentration of the target phase (i.e. MoAlB) with an orthorhombic base-centered crystal lattice was obtained. The three-dimensional structure has the following lattice parameters: a = 0.3206 nm, b = 1.3929 nm, and c = 0.3097 nm; the unit cell volume is 0.138301 nm3. At the same time, no significant difference can be observed in the lattice spacing of the MAB phase when excessive Al is introduced. The intermediates include a low-temperature tetragonal boride MoB, an intermetallic Mo3Al8 with a monoclinic syngony, as well as an Al2O3 phase identified by scanning electron microscopy and energy dispersive X-ray spectroscopy. Etching of the structure in an acid solution (HNO3 – HF – HCl) revealed that the MoAlB ceramics has a laminated structure with a layer thickness of 100–300 nm. Through nanoindentation, it was found that the MAB phase has a hardness of 11.6 GPa, an elastic modulus of 249.3 GPa, and an elastic recovery of 46%.This research was funded by the Russian Science Foundation under Project No. 21-79-10103.The authors would like to thank M. I. Petrzhik, Doctor of Technical Sciences, A. V. Novikov, Candidate of Technical Sciences, and N. V. Shvyndina for their support with specimen studies and discussion.