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The present work investigates microstructural and mechanical properties of B 4 C particulate-reinforced Al-8.5 wt% Si-3.5 wt% Cu matrix composites prepared by a successive process of mechanical alloying (MA), cold pressing, and pressureless sintering. The effects of B 4 C amount, milling duration, and heat treatment were investigated. The MA (for 0, 3, 5, and 7 h) in a high-energy vibratory ball mill was applied to elemental powder blends, in which 0, 5, 7.5, and 10 wt % B 4 C was incorporated as reinforcing particles. Mechanically alloyed (MAed) powders were uniaxially pressed and sintered for 2 h at 550 °C then subjected to an aging heat treatment to improve the mechanical properties. Based on XRD, SEM, and TEM microstructural investigations, compared to the as-blended case, the MAed powders possessed a semi-equiaxed morphology and homogenous structure, with higher lattice strain and smaller crystallite size. In addition, the Al-8.5 wt% Si-3.5 wt% Cu-xB 4 C (x = 0, 5, 7.5, and 10 wt%) composites consolidated from the MAed powders exhibited improved mechanical properties, including microhardness, wear resistance, and compressive strength. The hardness of the 5 h-MAed Al-8.5 wt% Si-3.5 wt% Cu–10B 4 C composite was 167 H V, and yield and compressive strength were 362 MPa and 454 MPa, respectively. This sample also exhibited one of the lowest wear rates, 5.82 × 10−5 mm3/m.N, roughly 17 and 10 times lower than that of the 5 h-MAed Al-8.5 wt% Si-3.5 wt% Cu sample and its as-blended counterpart, respectively. Furthermore, the hardness and compressive strength of 5 h-MAed Al-8.5 wt% Si-3.5 wt% Cu–10B 4 C composite increased to 231 H V and 475 MPa, respectively, after the age-hardening treatment. [ABSTRACT FROM AUTHOR]

In this study, in-situ synthesis of tungsten boride-carbide composite powders using a mechanochemical processing (MCP) method was investigated on the WO 3 –B 2 O 3 –Mg–C quaternary powder system. The raw blends of WO 3 –B 2 O 3 –Mg–C were processed in a high-energy ball mill for between 8 and 24 h. In addition to the MCP duration, excess B 2 O 3 or C reactants and ball-to-powder weight ratio (BPR) were tested as important process parameters which affected the resultant phases. After the mechanochemical reaction, the products were purified using 6 M HCl solution to eliminate the MgO by-product. FactSage 7.1 and HSC Chemistry Ver.4.1 thermochemical software was used to predict the thermodynamically possible reactions and products. Microstructural properties of the fabricated powders were inspected through X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM) and energy dispersive spectroscopy (EDS) techniques. Additionally, changes in particle size with duration of the MCP were determined for the synthesized powders. According to the XRD results, tungsten boride and tungsten carbide phases were obtained as the main reaction products for all reaction durations and reactant stoichiometries. Distribution of the total amounts of tungsten boride and tungsten carbide phases were determined respectively as 79.8 and 20.2 wt% for the 8 h-processed stoichiometric powders. However, the total tungsten boride amount decreased with the increasing MCP duration and its respective percentage was calculated as 57.1 wt% for the 24 h-processed stoichiometric powders. In addition, by increasing the processing duration to over 12 h, W 2 B, W 2 C and B 4 C phases were detected. When 200 wt% B 2 O 3 was added, the B:W ratio and total amount of tungsten boride phases in the synthesized powders increased. Similarly, by utilizing 200 wt% C, a significant increase in the B 4 C peaks together with W 2 C peaks was detected. Therefore, the properties of tungsten boride-carbide composite powders synthesized by the mechanochemical route are highly affected by the process parameters. [ABSTRACT FROM AUTHOR]