Experimental and Theoretical Study of Ultra-Hard AlMgB 14 -TiB 2 Composites: Structure, Hardness and Self-Lubricity

• Published in: Materials 2022-11, Vol.15 (23)
• Main Authors: Nikitin, Pavel, Zhukov, Ilya, Tkachev, Dmitrii, Abzaev, Yurii, Marchenko, Ekaterina, Vorozhtsov, Alexander
• Format: Article
• Language: English
• ISSN: 1996-1944; 1996-1944

It is known that the presence of oxygen phases in hard materials leads to an undesirable decrease in the mechanical properties. In materials based on AlMgB , the main oxygen impurity is spinel MgAl O ; it significantly reduces the hardness of AlMgB and its formation during sintering is inevitable. In this work, the ultra-hard spark plasma sintered (SPSed) AlMgB -TiB composite material was fabricated from the AlMgB -TiB precursor obtained by self-propagating high-temperature synthesis (SHS). Due to the high synthesis temperatures, the main oxygen phase in the obtained composite was Al B O instead of spinel MgAl O . It was found that the obtained composite has excellent mechanical properties. The maximum hardness of the sample is 44.1 GPa. The presence of oxygen in the form of the Al B O phase led to unexpected results: the friction coefficient of the obtained AlMgB -TiB composite under dry conditions against the Al O counter-specimen is approximately four times lower than the friction coefficient of pure ceramic AlMgB (0.18 against 0.7, respectively). Based on the observed results, it was found that the Al B O particles formed during the SHS are responsible for the low friction coefficient. The quantum chemical calculations showed that the elastic moduli of Al B O are significantly smaller than the elastic moduli of AlMgB and TiB . Thus, during sliding, Al B O particles are squeezed out onto the composite surface, form the lubricating layer and reduce the friction coefficient.