SiC-Based Composites Sintered with High Pressure Method

Abstract

Silicon carbide-based materials usually have high hardness (2500 – 2800 HV) and thus have superior wear resistance. Nevertheless, the tribological performance of SiC is determined by many factors, such as the grain size of mated materials or the reactions in the presence of oxygen and humidity in the surrounding atmosphere. For example, in unlubricated sliding, wear resistance of SiC ceramics can be greater in air than in inert atmosphere owing to thin soft oxide films reducing friction and local surface pressure. (Gahr et al., 2001; Guicciardi et al., 2007). The friction and wear properties of SiC materials (both in dry and lubricating conditions) have been studied extensively because they are used in applications like bearings, cylinder liners and mechanical seals (Murthy et al., 2004). Silicon carbide-based ceramics have high melting point (~2500 °C), high thermal conductivity (43 – 145 W/m·K – depending on a temperature and phase composition), low thermal expansion (~4,5×10-6·K-1), and high temperature capability. Silicon carbide is a semiconductor which can be doped n-type by nitrogen or phosphorus and p-type by aluminium, boron, gallium or beryllium. Due to the combination of its thermal and electrical properties, SiC is applied in a resistance heating, flame igniters and electronic components. Relatively pure SiC has also an excellent corrosion resistance in the presence of hot acids and bases (Richerson, 2004). Silicon carbide powder compacts are difficult to densify without additives because of the covalent nature of the Si–C bonds and the associated low self-diffusion coefficient. Therefore, Reaction Sintering (RS) in the presence of liquid silicon as well as Hot Isotactic Pressing (HIP) are frequently used to obtain a high quality, full dense SiC ceramics. Typical room temperature flexural strength of SiC-based materials is about 350-550 MPa. High-strength RS-SiC (over 1000 MPa in a 3-point bending test) was developed by controlling the residual Si size under 100 nm. (Magnani et al., 2000; Suyama et al., 2003). Silicon carbide ceramics have the ability to increase in strength with increase of temperature. It was reported that flexural strength of some kind of commercial SiC ceramic increase is from 413 MPa at the room temperature to around 580 MPa at 1800 °C (Richerson, 2004). For hot-pressed silicon carbide with addition of 0.15-1.0 wt% Al2O3, the high-temperature strength has been improved from 200 MPa to 700 MPa by decreasing the grain boundary concentration of both Al and O at 1500 °C (Kinoshita et al., 1997).