| Ti3SiC2 is known as a remarkable material for a myriad of applications, because of its unique combination of metallic and ceramic properties. At room temperature, it has excellent electrical and thermal conductivities. It displays high melting point, high yield strength, high thermal stability. Those excellent properties make Ti3SiC2 to be expected to use as brush electrode materials, electrical contact materials, low coefficient of friction materials, machinable ceramic materials, heat exchangers, special mechanical seals and high temperature structures. However, Ti3SiC2 material has poor oxidation resistance above 1100 ℃. In addition, its high temperature strength could also be greatly reduced due to its high temperature plastic deformation.In this study, Ti3SiC2, Ti3SiC2/A12O3 composites and Ti3SiC2/MgAl2O4 composites were fabricated by reactive hot pressing method using Ti, TiC, Si as raw materials and A12O3, MgAl2O4 powders as additions. The influence of hot-pressing temperature, addition species and content on the phase composition, volume density, microstructure, mechanical properties of Ti3SiC2 matrix composites was studied. In addition, effect of the oxidation temperature, addition species and content on oxidation resistance of Ti3SiC2 matrix composites was investigated by the study to oxidation weight curve and the phase composition of samples, the surface and fracture morphologies of oxide layer. Conclusions as follows:(1) The phase composition anylysis and microstructure observation showed: ①The main phases of composites were Ti3SiC2 and additions, TiC as minor phase embedded in Ti3SiC2. ② Increasing hot pressing temperature was advantageous to improve the generation of Ti3SiC2. However, the hot pressing temperature was not too high; ③The dense Ti3SiC2 composites could be fabricated at 1450 ℃; ④Introducing the appropriate content of Al2O3 and MgAl2O4 could promote the growth and development of Ti3SiC2.(2) Mechanical property test to materials showed: ①There were several energy absorbing mechanisms during the composites fracture such as intragranular fracture, crack deflection, grain delamination, grain pullout, et al. These energy absorbing mechanisms could increase the flexural strength and fracture toughness. ②The flexural strength and fracture toughness of composites was increased with increasing hot pressing temperature; ③Introducing the appropriate content of Al2O3 and MgAl2O4 could promote the growth and development of Ti3SiC2 and prevent the expansion of the crack, and then improve the mechanical performance of Ti3SiC2 matrix composites. However, when the content of Al2O3 and MgAl2O4 was too high, the mechanical properties of the composites will be reduced.(3)The isothermal oxidation behaviors of Ti3SiC2 matrix composites had been investigated at 1100~1500 ℃ in air. The results showed that: ①The main oxidation products of Ti3SiC2 were rutile and cristobalite. The oxidation layers were composed of two layers, the outer was consisted of TiO2, and the inner was a two-phase mixture of TiO2 and SiO2. A large number of pores existed in oxide layers which leading to a poor oxidation resistance. ②For Ti3SiC2 matrix composites, rutile grains in oxidation layers were refined due to the introduction of the second phase. The volume expansion caused by reactions between Al2O3(or MgAl2O4) and Ti O2 could close pores and improve the densification of oxide layers, which further improve the oxidation resistance of Ti3SiC2/Al2O3 and Ti3SiC2/MgAl2O4. ③As for the oxidation of Ti3SiC2/SiC, the SiO2 content in oxidation layers was increased from the oxidation of SiC. The dense SiO2 layer acted as a protective film which could prevent the inward diffusion of oxygen. Moreover, liquid phase under high temperature could also fill the pores in oxidation layers. Thus, Ti3SiC2/SiC composite had the best oxidation resistance among three Ti3SiC2 matrix composites. |
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