Microstructure and mechanical properties of the ZrC-added Mo-Si-B alloys prepared by arc-melting

ZrC-added Mo-Si-B alloys were prepared by arc-melting. After heat-treatment at 1800°C for 24 h, their density and elastic moduli were measured, and their microstructure was evaluated. Moreover, high-temperature compression tests at 1400°C and four-point bending tests with a Chevron notch at room temperature were conducted to investigate their mechanical properties. The primary phase was Mo solid solution (Mo_ss) or ZrC depending on Mo/ZrC compositional ratio. After the primary phase crystallization, Mo₂B, Mo₅SiB₂(T₂), Mo_ss+ ZrC eutectic, Mo_ss+ T₂eutectic and/or Mo_ss+ Mo₃Si + T₂eutectic were crystallized out during solidification. Mo2B and/or Mo3Si dissolved during the heat treatment in some alloys. The ZrC-added Mo-Si-B alloys had higher high-temperature strength compared with the ternary Mo-Si-B alloys even though ZrC-added Mo-Si-B alloys contained less volume fraction of the T₂. Besides, the ZrC-added Mo-Si-B alloys exhibited better fracture toughness than that of ternary Mo-Si-B alloys, reaching 20.2 MPa(m)^1/2. Therefore, this study found that ZrC plays a significant role in improving high-temperature strength and fracture toughness in Mo-Si-B alloys.