Mechanical properties and scratch test studies of new ultra-hard AlMgB 14 modified by TiB 2

Abstract

Nanoscale composites of AlMgB 14 with AlN, TiC or TiB 2 were prepared by mechanical alloying in a vibratory mill, followed by compression molding at 1400 °C. Determination of microhardness and fracture toughness indicated that TiB 2 was an effective addition for increasing both quantities. The optimum percent TiB 2 addition corresponding to the highest hardness and fracture toughness was 60–70 wt%. The abrasion resistance of AlMgB 14 composites with varying amounts of TiB 2 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 TiB 2 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 Al 2MgO 4 (spinel) and FeB 4O 7 in AlMgB 14. Cracks were observed on the surface of AlMgB 14−70 wt% TiB 2 when scratched under 70 N load, but there was no cracking in the absence of TiB 2.