Effects of reinforcement content and sequential milling on the microstructural and mechanical properties of TiB₂ particulate-reinforced eutectic Al-12.6 wt% Si composites

This study reports the effects of reinforcement content (2, 5 and 10 wt%) and sequential milling on the microstructural, physical and mechanical properties of the TiB₂ particulate-reinforced Al-12.6 wt% Si metal matrix composites (MMCs) prepared starting from Al, Si and TiB₂ elemental powders. Sequential milling process included two different kinds of high-energy ball milling such as mechanical alloying (MA) and cryomilling (CM). MA experiments were carried out at room temperature for 4 h using a Spex™ 8000D Mixer/Mill. Subsequent CM experiments were conducted with externally circulated liquid N ₂ for 10, 20 and 30 min using a Spex™ 6870 Freezer/Mill. Milled powders were compacted by cold uniaxial pressing under a pressure of 450 MPa and then by cold isostatic pressing (CIP) under 400 MPa. The green bodies were sintered at 570 °C for 2 h under Ar atmosphere. Characterization investigations of the samples were performed using X-ray diffractometer (XRD), TOPAS software, scanning electron microscope/energy-dispersive spectrometer (SEM/EDS) and particle size analyzer (PSA). Sintered samples were also characterized in terms of Archimedes density, Vickers microhardness and relative wear resistance. Composites sintered from the mechanically alloyed (MA’d) and 20 min of cryomilled (CM’d) powders exhibited the higher microhardness values than those of other sintered samples. Wear rates of the sintered samples slightly increased with increasing CM time. At a constant CM time of 20 min, wear rates incredibly decreased as TiB₂ content increased.