Effect of Carbon Addition and Mixture Method on the Microstructure and Mechanical Properties of Silicon Carbide

Abstract

High dense (>99% density) SiC ceramics were produced with addition of C and B4C by spark plasma sintering method at 1950 °C under 50 MPa applied pressure for 5 min. To remove the oxygen from the SiC, it was essential to add C. Two different mixture method were used, dry mixing (specktromill) and wet mixing (ball milling). The effect of different levels of carbon additive and mixture method on density, microstructure, elastic modulus, polytype of SiC, Vickers hardness, and fracture toughness were examined. Precisely, 1.5 wt.% C addition was sufficient to remove oxide layer from SiC and improve the properties of dense SiC ceramics. The highest hardness and elastic modulus values were 27.96 and 450 GPa, respectively. Results showed that the 4H polytype caused large elongated grains, while the 6H polytype caused small coaxial grains. It has been observed that it was important to remove oxygen to achieve high density and improve properties of SiC. Other key factor was to include sufficient amount of carbon to remove oxide layer. The results showed that excess carbon prevented to achieve high density with high elastic modulus and hardness.

Effect of AlN addition on the electrical resistivity of pressureless sintered SiC ceramics with B4C and C

“…The polished specimens (1 μm) were etched using a modified Murakami's reagent. 17 The etched microstructure was observed by SEM. The aspect ratio of platelet grains was defined as the ratio of the longest to shortest diameter passing through the centroid of a grain.…”

“…Pyrolysis of polycarbosilane polyme by Key et al 43 content due to increased phonon scattering caused by Al-dopants in the SiC lattice of SiC ceramics sintered at 2170°C in Ar with 0.6 wt% B 4 C and 1.5 wt% C. 7 There are few reports on the electrical properties of PSS SiC ceramics with AlN. Ou et al [13] reported an electrical resistivity of 10 4 -10 7 Ω cm for SiC-10-51 wt% AlN ceramics hot-pressed at 2100°C with 0.2 wt% B and 1 wt% C. The reported electrical resistivity of bulk SiC-AlN ceramics varies from 10 4 -10 17 Ω‧cm depending on the AlN content, sintering additives, and processing conditions. 13−16 In a previous work on hot-pressed SiC-AlN ceramics without sintering aids, it was demonstrated that adding AlN increased the electrical resistivity due to the formation of electrically insulating SiC-AlN 2H solid-solution (2H ss ) phase.…”

Pressureless solid-state sintering of SiC ceramics with BN and C additives

“…The sintered density was measured using the weight to volume ratio of the sintered specimens. The polished specimens were etched using a modified Murakami's reagent [14]. For the phase identification, sintered samples were ground and analyzed using X-ray diffraction (XRD; D8 Discover, Bruker AXS Gmbh, Karlsruhe, Germany).…”

Special Issue: Silicon Carbide: From Fundamentals to Applications

“…References [ 4 , 5 ] can be attributed to the second group of works, which describe technologies that improve the properties of both ceramics based on silicon carbide and the properties of nanostructures made of silicon carbide. The authors of Reference [ 4 ] added carbon and B4C to create ceramics with high density. In doing so, they used the method of spark plasma sintering at a temperature of 1950 °C with the simultaneous creation of a pressure of about 50 MPa for 5 min.…”

“…In doing so, they used the method of spark plasma sintering at a temperature of 1950 °C with the simultaneous creation of a pressure of about 50 MPa for 5 min. Carbon was added by the authors of Reference [ 4 ] to remove oxygen from the SiC ceramic. It turned out that the addition of about 1.5 wt.% C leads to almost complete removal of the oxide layer from SiC.…”