The effect of lamellar structure in Mo5Si3-MoSi2 alloy refined by annealing on the Vickers hardness at room temperature

Lamellar structure consisted of Mo5Si3 (D8m) phase and MoSi2 (Cllb) phase was observed in all the alloys. For Mo5Si3-MoSi2 eutectic alloy, a typical eutectic microstructure with primary Mo5Si3 phase and Mo5Si3/MoSi2 lamellar structure was observed, and the primary Mo5Si3 phase was eliminated when annealing at 1200 °C for over 24 h. For Mo5Si3-MoSi2 hypoeutectic alloy, the lamellar structure was found only after annealing. A full lamellar structure throughout the alloy developed well with fine spacing on the order of 100 nm after annealing at 1200 °C for 48 h. For Mo5Si3-MoSi2 hypereutectic alloy, the lamellar structure was found both before and after annealing. Primary MoSi2 was observed in the alloy even after annealing at 1200 °C for 96 h, although the volume fraction of lamellar structure was increased with prolonging annealing time. The effect of the formation, development and destruction of lamellar structure on Vickers hardness and indentation toughness of alloys was investigated. The Vickers hardness and indentation toughness of Mo5Si3-MoSi2 hypoeutectic alloy show a same regularity, that is, they increase with prolonging annealing time and development of lamellar structure. The highest Vickers hardness and indentation toughness are about 1470 HVN and 4.8 MPa m1/2, respectively. The Vickers hardness and indentation of Mo5Si3-MoSi2 eutectic alloy and Mo5Si3-MoSi2 hypereutectic alloy are all roughly constant with prolonging annealing time, that is, about 1400 and 1270 HVN for Vickers hardness and 4 and 3.2 MPa m1/2 for indentation toughness.