Si3N4@SiO2/PEEK core-shell structure ceramic matrix composite prepared by cold sintering and its tribological properties

The traditional high-temperature sintering method cannot achieve the combination of ceramics and polymers for the huge sintering temperature difference. The insufficient interfacial bonding strength of the ceramic matrix is the difficulty in the low-temperature preparation of ceramic-polymer composites. To improve the interfacial bonding strength of Si3N4 (Silicon nitride) ceramic matrix composite, an easy-bonding SiO2 (Silica) shell was introduced onto the surface of the hard-bonding Si3N4 core by Stober method, to obtain Si3N4@SiO2 composite. Si3N4@SiO2/PEEK (Polyetheretherketone) composites were prepared by the cold sintering process (500 MPa, 240 °C, and transient liquid phase is NaOH solution). The dry tribological properties of Si3N4@SiO2/PEEK composites with different PEEK percentages were studied by a ball-disc contact form. It is shown that an amorphous SiO2 shell with a thickness of 25 nm is chemically bonded onto the surface of the Si3N4 core. The presence of the SiO2 shell improves the interface bonding strength between Si3N4 ceramic particles. The friction coefficients of Si3N4@SiO2/PEEK composites decrease with the increase of PEEK percentage. Compared with Si3N4@SiO2 composite, the friction coefficient and wear rate of Si3N4@SiO2/50 vol% PEEK composite decrease by about 40% and 26%, respectively. The main wear forms of Si3N4@SiO2/PEEK composites are abrasive wear and adhesive wear. A mixed lubrication layer, mainly including PEEK, Si3N4, and SiO2, exists simultaneously on the surfaces of Si3N4@SiO2/PEEK composite and the counterpart ball, respectively, playing the role of reducing friction and wear.