Abstract：
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 AlMgB14, the main oxygen impurity is spinel MgAl2O4; it significantly reduces the hardness of AlMgB14 and its formation during sintering is inevitable. In this work, the ultra-hard spark plasma sintered (SPSed) AlMgB14-TiB2 composite material was fabricated from the AlMgB14-TiB2 precursor obtained by self-propagating high-temperature synthesis (SHS). Due to the high synthesis temperatures, the main oxygen phase in the obtained composite was Al4B2O9 instead of spinel MgAl2O4. 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 Al4B2O9 phase led to unexpected results: the friction coefficient of the obtained AlMgB14-TiB2 composite under dry conditions against the Al2O3 counter-specimen is approximately four times lower than the friction coefficient of pure ceramic AlMgB14 (0.18 against 0.7, respectively). Based on the observed results, it was found that the Al4B2O9 particles formed during the SHS are responsible for the low friction coefficient. The quantum chemical calculations showed that the elastic moduli of Al4B2O9 are significantly smaller than the elastic moduli of AlMgB14 and TiB2. Thus, during sliding, Al4B2O9 particles are squeezed out onto the composite surface, form the lubricating layer and reduce the friction coefficient.
摘要：
已知在硬质材料中氧相的存在导致机械性能的不期望的降低。在基于AlMgB14的材料中，主要的氧杂质是尖晶石MgAl2O4；它显着降低了AlMgB14的硬度，并且在烧结过程中不可避免地形成了AlMgB14。在这项工作中,超硬放电等离子烧结（SPSed）AlMgB14-TiB2复合材料是由自蔓延高温合成（SHS）获得的AlMgB14-TiB2前体制成的。由于合成温度高,所得复合材料中的主要氧相是Al4B2O9，而不是尖晶石MgAl2O4。发现所获得的复合材料具有优异的机械性能。样品的最大硬度为44.1GPa。Al4B2O9相形式的氧的存在导致意想不到的结果:所得AlMgB14-TiB2复合材料在干燥条件下对Al2O3反样品的摩擦系数比纯陶瓷AlMgB14的摩擦系数低约四倍(分别为0.18对0.7)。根据观察到的结果，发现在SHS期间形成的Al4B2O9颗粒是低摩擦系数的原因。量子化学计算表明，Al4B2O9的弹性模量明显小于AlMgB14和TiB2的弹性模量。因此，在滑动过程中，Al4B2O9颗粒被挤出到复合材料表面，形成润滑层，降低摩擦系数。
