MoSi 2 is the most potential high temperature structural materials that can be used in aerospace and aviation industry. But its fracture toughness is low and its low temperature oxidation resistance is poor, which limits its application. To solve these problems, novel MoSi 2 @ZrO 2 core-shell composites were prepared by spark plasma sintering (SPS) at 1300 °C⁓1500 °C. The influences of sintering temperatures on the microstructures, mechanical properties and tribological properties of the composites were studied. It was found that the relative density, Vickers hardness , bending strength and fracture toughness of the composites first ascended and then descended with the sintering temperature rising from 1300 °C to 1500 °C. As the sintering temperature reached 1400 °C, the maximum relative density, the maximum Vickers hardness , the maximum bending strength and the maximum fracture toughness of the composite material achieved 97.5%, 1103 HV, 540 MPa and 7.96 MPa·m 1/2 , respectively. Additionally, the friction coefficient of the composite materials first descended and then ascended with sintering temperature rising. As the sintering temperature reached 1400 °C, the minimum friction coefficient was about 0.355. Moreover, we analyzed the relations between the mechanical properties and microstructure. The toughening mechanisms of the MoSi 2 @ZrO 2 composites were also discussed. In addition, during cyclic isothermal oxidation at below 600 °C, weight gains of the MoSi 2 @ZrO 2 composites evidently decreased, compared with that of pure MoSi 2 , proving better low-temperature oxidation resistance .
Lu Zhu,Xuanru Ren,Xiaohong Wang,Xueqin Kang,Ruixin Zheng,Peizhong Feng
Spent MoSi 2 heating elements, which worked in the industrial electrical furnace at high temperature, were crushed into powders and reused as coating raw materials. ZrO 2 was added into spent MoSi 2 powders to fabricate MoSi 2 -ZrO 2 coatings on niobium by spark plasma sintering, and the microstructure and oxidation behavior of the coatings at 1500 and 1700 °C were explored. The results showed that cracks exist in MoSi 2 coating while ZrO 2 -containing coatings are crack-free with the formation of (Mo,Nb) 5 Si 3 diffusion layer after SPS, indicating good metallurgical bonding. After oxidation at 1500 °C for 20 h, the lowest mass gain is obtained by MoSi 2 -30ZrO 2 coating. SiO 2 and ZrSiO 4 are formed on the composite coatings at elevated temperature, which improves the high-temperature oxidation resistance. After oxidation at 1700 °C for 60 min, the oxide scale of MoSi 2 -30ZrO 2 coating is dense without any voids or cracks, demonstrating better high-temperature oxidation resistance than that of single MoSi 2 coating.
MoSi 2 is a promising candidate for high-temperature, structural materials. However, their oxidation resistance is poor below 600 °C. To prevent MoSi 2 from being oxidized at low temperatures, core-shell structured MoSi 2 @ZrO 2 powder were prepared by hydrothermal-calcination approach. First, MoSi 2 @Zr(OH) 4 core-shell composite powder with nano-sized Zr(OH) 4 shell particles were synthesised using a hydrothermal method . Subsequently, the MoSi 2 @ZrO 2 core-shell structured powder were obtained by calcination of the MoSi 2 @Zr(OH) 4 powders at 900 °C for 2h. Finally, microstructure and oxidation behaviour of the MoSi 2 @ZrO 2 powder at 400 °C–600 °C in air were investigated systematically. Microstructural analysis revealed that all samples had a distinct core-shell structure, and the ZrO 2 shells coated the surface of the MoSi 2 core. Oxidation behaviour studies showed that the dense ZrO 2 shell layer could isolate the MoSi 2 surface from oxygen, improving the low-temperature oxidation resistance and providing better low-temperature antioxidant properties than those of the MoSi 2 and MoSi 2 @Zr(OH) 4 core-shell structures.
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