| Silicon nitride and sialon ceramics are quickly developed in the 1970s. They process many advantages, for examples, high strength, hardness and temperature resistance, and excellent thermal and electrical properties, which make the two materials widely used in industry. However, silicon nitride and sialon have the common faults of ceramic material:low toughness and high sintering temperature, which limit their wider applications. The performances of intermetallic compounds lie between those of metals and ceramics, and they have been employed to improve the mechanical properties of alumina ceramics. However, there are few research reports about improving the mechanical performances of silicon nitride and sialon ceramic by intermetallic compounds.In this article, Fe-Si/sialon, CNTs/Fe-Si/sialon and Fe-Si/Si3N4 composites were in situ synthesized using reaction hot-pressing sintering technique with the intermetallic compound of Fe3Al as raw material. And the mechanical properties of composites and the toughening mechanism of Fe3Al and CNTs in ceramic were studied. In addition, (TiAlSi)N coating with good hardness and wear resistant were prepared on the surface of Fe-Si/Si3N4 composites by magnetron sputtering technology, and its morphology was also studied. The main results are as follows:(1) Fe-Si/sialon composites were successfully fabricated using Fe3Al as raw material by reaction hot-pressing sintering at 1600 ℃ in N2 atmosphere. The appropriate amount of Fe3Al can improve the fracture toughness by increasing density of composites, and forming crack bridging and deflection during crack propagation. The flexure strength, fracture toughness and hardness of Fe-Si/sialon composites were about 146.3%,73.3% and 5.9% higher than those of the monolith, respectively. In addition, Al2O3 acted as one of the reactions to generate sialon, whose additive amount also played a certain effect on the phase composition and performance of the composites. When the additive amount of Al2O3 was 20 wt%, the fracture toughness, hardness and flexure strength were 5.7 MPa-m1/2,16.2 GPa, and 500 MPa, respectively.(2) CNTs/Fe-Si/sialon composites were prepared at the low temperature of 1600 ℃ by reaction hot-pressing sintering with Si3N4, Al2O3, CNTs and Fe3Al as starting materials, and mechanical properties and microstructure of the composites were investigated. The research results showed that the combined Fe3Al and CNTs could improve the mechanical properties of matrix greatly, with fracture toughness increasing from 4 to 6.7 MPa-m1/2, hardness increasing from 13.3 to 13.7 GPa. Crack deflection and bridging resulted from Fe-Si, pullout and bridging of CNTs, and enhanced self-toughening effect were dominantly responsible for the improvement of fracture toughness.(3) Fe-Si/Si3N4 composites were in situ synthesized with optimum fracture toughness at 1750 ℃ with Si3N4 and Fe3Al as starting materials. Research results showed that the addition of Fe3Al particles facilitated the growth of Si3N4 grains, resulting in the increase yield of elongated Si3N4 grains. The composites incorporated with 4 wt% Fe3Al possessed the best fracture toughness of 8 MPa-m1/2, and 123.1% higher than that of the monolith.(4) Experimental results showed that Fe3Al can play important roles in preparing and toughening sialon ceramics and Si3N4 ceramics. The toughening mechanism of Fe-Si mainly included:crack deflection, crack bridging, and enhanced self-toughening effect. The small nanopores distributing on the interface between the reinforcement and the matrix could effectively improve the toughness of the composites. On one hand, they could weaken the interface bonding strength enhanced by interfacial reactions, and increase the crack propagation path to improve the toughness. On the other hand, it could effectively reduce the stress concentration at the crack tip and inhibit the crack propagation.(5) Hard wear-resistant (TiAlSi)N coating which was prepared using the magnetron sputtering technology could be employed to improve the wearability of Fe-Si/Si3N4 composites. When the bias was 100 V, TiAl target current was 0.2 A, Si target current was 0.3 A and deposition time was 2 h, the thickness of the coating was 0.91 μm, the friction coefficient was 0.23, and the hardness reached to 21.3 GPa. By contrast with the friction coefficient (0.62) and hardness (14.1 GPa) of substrate material, (TiAlSi)N coating improved the friction coefficient and hardness greatly. |
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