Characterization investigations of a Al-5 wt.% Si/2 wt% (NbB2, NbC) hybrid composite fabricated via mechanically alloying and sequentially milling (mechanical alloying + cryomilling)

In this study, microstructural and mechanical properties of a Al-5 wt.% Si/2 wt% (NbB₂, NbC) composite synthesized by sequentially milling (mechanical alloying (MA) and/or cryogenic milling(CM)) were investigated. Nb2O5, B2O3 and C powder blends were milled using high energy milling for 5 h and annealed at 1400 °C for 12 h to produce NbB₂-NbC hybrid powders. The NbB₂-NbC hybrid powders were mixed with the matrix Al-5 wt.% Si powders to constitute the Al-5 wt.% Si/2 wt.% (NbB₂-NbC) powders blends which were mechanically alloyed (MA'd) for 4 h using Spex™ Mixer/Mill, cryo-milled for 10 min in a Spex™ 6870 Freezer/Mill and finally MA’d for 1h in Spex™ Mixer/Mill again. As-blended, MA’d and cryomilled powders were compacted in a hydraulic press with a uniaxial pressure of 450 MPa. Compacted samples were sintered at 570°C for 2 h under Ar gas atmosphere. Microstructural characterizations of the as-blended/MA'd powders and the sintered composites were performed using X-ray diffractometry (XRD) and scanning electron microscopy (SEM) techniques. Density and microhardness measurements and sliding wear tests were performed on the sintered composite samples. Sequentially milled and sintered Al-5 wt.% Si-2 wt.% (NbB₂-NbC) samples had the highest mean microhardness value (2.29 ± 24.98 GPa) and the lowest wear volume loss (0.038 mm3).