Phase and microstructural characterization of Mo–Si–B multiphase intermetallic alloys produced by pressureless sintering

•Active and ultra-fine Mo–Si–B powders were produced by mechanical alloying.•The phases of MoSi2 and MoB were obtained by sintering Mo–57Si–10B at 1400°C for 2h.•Composite based on MoB/MoSi2 was obtained by sintering Mo–47Si–23B at 1300°C for 3h.•High content of MoB in the composite based on MoB/MoSi2 increased density.•High hardness of the composite based on MoB/MoSi2 is related to MoB matrix. In this study Mo–47Si–23B and Mo–57Si–10B powders (at.%) was milled for 20h in attritor ball mill with a rotational speed of 365rpm and the ball/powder mass ratio 20/1. After degassing of As-mechanically alloyed powders at 450°C, the powders were pressed into cylindrical samples with 25mm diameter under 600MPa pressure. The samples were sintered by using of a tube resistance furnace under Ar atmosphere. Phase and microstructure characteristic of mechanically alloyed powders and sintered samples, were investigated by scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. Also hardness test was performed. Homogeneous distribution of active and ultra-fine powders were obtained after milling for 20h. Mo–57Si–10B alloy with MoB and MoSi2 dominant phases was produced by sintering at 1400°C for 2h. Dominant phases similar to Mo–57Si–10B alloy sintered at 1400°C for 2h could be synthesized in Mo–47Si–23B alloy after sintering at 1300°C for 3h, but volume fraction of MoB phase was different. The Mo–47Si–23B alloy contained a higher phase fraction of MoB compound as compared to Mo–57Si–10B alloy. Very high density in Mo–47Si–23B alloys was obtained, due to the presence of high volume fraction of MoB phase. Formation heat of MoB acted as a positive potential to increase driving force of sintering and consequently bulk density. Finally, a uniform and fine distribution of MoSi2 particles in MoB continuous matrix in the microstructure of Mo-47Si-23B alloys led to the high hardness up to 660 Vickers.