Mechanical properties and scratch test studies of new ultra-hard AlMgB14 modified by TiB2

Nanoscale composites of AlMgB14 with AlN, TiC or TiB2 were prepared by mechanical alloying in a vibratory mill, followed by compression molding at 1400 °C. Determination of microhardness and fracture toughness indicated that TiB2 was an effective addition for increasing both quantities. The optimum percent TiB2 addition corresponding to the highest hardness and fracture toughness was 60–70 wt%. The abrasion resistance of AlMgB14 composites with varying amounts of TiB2 has been studied using single-point diamond scratch tests with loads ranging from 20 to 70 N in 10 N increments. The scratch width, as measured by stylus profilometer, increased almost linearly with the applied load and decreased with increasing TiB2 proportion up to 70 wt%. Furthermore, macroscopic abrasion resistance increased with both mean hardness and fracture toughness. Energy dispersive spectroscopy (EDS) revealed the presence of Al2MgO4 (spinel) and FeB4O7 in AlMgB14. Cracks were observed on the surface of AlMgB14−70 wt% TiB2 when scratched under 70 N load, but there was no cracking in the absence of TiB2.