Dr. Pavol Hvizdos, Director, Institute of Materials Research, Slovak Academy of Sciences, Slovakia

Title: Development of new SiC nanocomposites with enhanced electrical conductivity

Abstract: New types of Silicon carbide based nanocomposites were developed with the aim of increasing their electrical conductivity, so that they can be used in wider functional ways and also to explore the possibility to machine them using electrical discharge machining, all of this without lowering their other properties such as hardness, wear resistance, chemical and thermal stability.

The first type was SiC containing conductive carbide phase TiNbC. The other two types contained carbon nanofillers: nanotubes and graphene platelets. The prepared materials were compacted using standard hot pressing (HP), spark plasma sintering (SPS), and rapid hot pressing (RHP). Their microstructure, chemical and phase composition were studied in detail, the results showed successful microstructure design and confirmed desired composition. In all cases a reference material, a single phase SiC, prepared by the same ways, was used for comparison.

As the base, series of three optimized SiC-TiNbC (with 30, 40 and 50 wt. % of TiNbC) composites were developed. Increase in electrical conductivity by four orders was achieved without compromising the mechanical and tribological properties. Technological tests showed possibilities to machine these materials by electric discharge technique as well as other non-conventional methods.

The materials with carbon based nanofillers included SiC-graphene and SiC-CNT (carbon nanotubes). Methods of their preparation were optimized, mainly to achieve a good distribution of the carbon nanophases.

In SiC-graphene (graphene nanoplatelets and reduced graphene oxide - up to 5 wt%) the rapid hot press (RHP) technique was successfully developed and tested, and materials with graphene nanoplatelets and reduced graphene oxide were produced. Both types reached satisfactory parameters with respect to their microstructure and basic mechanical properties. Their electrical conductivity increased by four orders which clearly shows their potential.

In SiC-CNT (with up to 10 wt% CNT) a new technique of in-situ CNT preparation by CCVD was developed. This enabled to solve the problem with distributing of CNTs and in this way to increase the electrical conductivity by about three orders of magnitude.

In materials with carbon additives mechanical properties were slightly reduced, mostly due to increase of porosity, this fact however usually did not lead to lower strength or wear resistance.

Keywords: ceramics, silicon carbide, composites, CNT, graphene, wear, electrical conductivity