| 其他摘要 | As one of the layered ternary ceramics Mn+1AXn phase, in which M is a transition metal, A is IIIA or IVA element, X is C or N, Ti3SiC2 possesses a unique combination of the properties of both metal and ceramic, such as low density, high strength and modulus, good thermal and electrical conductivity, damage tolerance to thermal shock and oxidation below 1100℃, and most of all, good machinability.
However, the application of Ti3SiC2 was limited because of its weakness such as low hardness (Vickers hardness of 4 GPa), poor wear resistance and unsatisfied oxidation above 1100℃.
Previous study of Ti3SiC2 investigating on the electric structure indicated that the essential reason of the low hardness and poor wear resistance of Ti3SiC2 was weak bonding between the Ti-C-Ti-C-Ti covalent bond chain and Si atomic layer. Poor oxidation resistance above 1100℃ was caused by lack of continues SiO2 layer on the surface of the oxidation sample.
Titanium silicon, Ti5Si3, is one of candidates added into Ti3SiC2 to enhance the hardness and wear resistance for several reasons. First, Ti5Si3 has low density (ρ = 4.32 g/cm3), high melting point (2403 K), high Vickers hardness, good temperature strength and excellent oxidation resistance. In addition, Ti5Si3 has relatively high thermal and electrical conductivity. It’s more important that Ti5Si3 has approximate thermal expansion coefficient to that of Ti3SiC2. Hence, Ti5Si3 was chosen to prepare Ti3SiC2/Ti5Si3 composites in order to enhance the hardness and wear resistance of Ti3SiC2.
Near-fully dense Ti3Si(Al)C2/Ti5Si3 composites were synthesized by in situ hot pressing/solid-liquid reaction process under a pressure of 30 MPa in a flowing Ar atmosphere at 1580℃ for 60 min. The effect of Ti5Si3 on microstructure, density, Vickers hardness, flexural strength, fracture toughness and compressive strength of Ti3Si(Al)C2/Ti5Si3 composites were investigated. And then the oxidation resistance, friction and wear resistance of Ti3Si(Al)C2/Ti5Si3 composites were also investigated systematically.
Compared to monolithic Ti3Si(Al)C2 ceramics, Ti3Si(Al)C2/Ti5Si3 composites exhibit higher Vickers hardness and improved wear resistance, but a slight loss in flexural strength (about 26% lower than Ti3Si(Al)C2 matrix). Ti3Si(Al)C2/30 vol.%Ti5Si3 composite shows the highest Vickers hardness (68% higher than that of Ti3Si(Al)C2) and best wear resistance (the wear resistance increases by 2 orders of magnitude). And Ti3Si(Al)C2/Ti5Si3 composites maintain a high fracture toughness (The fracture toughness of Ti3Si(Al)C2/Ti5Si3 composites varies from 5.69 MPa•mm1/2 to 6.79 MPa•mm1/2).
The improvement in the properties is mainly ascribed to the contribution of Ti5Si3 particles, the hard Ti5Si3 particles nailed the soft Ti3Si(Al)C2 matrix and reduced the wear losses under the sliding steel ball. And the strength degradation is mainly due to the lower flexural strength of Ti5Si3. |
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