Research in the Design and Applications of Nanocomposite Coatings

This research is based upon the design and evaluation of coating technologies such as Physical Vapour Deposition (PVD), Microwave Plasma Chemical Vapour Deposition (MPCVD), and Thermal Spraying (TS). Research in the area of PVD and MPCVD coatings have focused in the developing of tribological coatings and plasma materials. Research in TS coatings includes Numerical modelling and durability evaluations for a number of industrial sectors.

Evaluation of these nanocomposite coatings include state of the art nanofatigue evaluations relating the impact of interactions of nanoparticles. Figure 1 shows an example of the interfacial debonding after nanofatigue in a 100nm diamond like carbon (DLC) coating used in solar cell industry.

Figure 1, Interfacial debonding of a 100nm DLC coating after nanofatigue tests.

Thermal Spray Coatings

Thermal spray is a molten or a semi-molten state process in which impacting particles land on a prepared substrate or an underlying lamella. These coatings can be designed to have nano-structural features to improve coatings performance. Following is a short presentation on thermal spraying and its tribological applications.

What is Thermal Spraying?

Failure modes and wear mapping of thermal spray coatings in rolling sliding contact

The design of surface coatings for tribological applications requires not only a thorough understanding of the tribological conditions e.g. contact stress, lubrication and friction but also the influence of coating processes, material, thickness and the role of substrate material properties. Tribologists often have little choice about the former but can influence the coating performance by appropriate selection of the latter. This research addresses the design of such overlay coatings produced by thermal spraying process and whilst introducing the wear maps based upon the understanding of failure modes and performance, also indicates the current achievements and reliability issues related to the design of such coatings.

Post-treatment of thermal spray coatings

The aim of this EPSRC funded research is to integrate the two process technologies of thermal spraying and Hot Isostatic Pressing (HIPing) of cermets to investigate their conjoint performance and potential for existing and novel tribological applications. These applications include metal and paper rolls and rollers, shafts, drilling and mining tooling, dies, metalworking equipment, bearings and gears. Previous studies on thermal spray coatings have shown that, whilst it is possible to minimise porosity using advanced technologies such as High Velocity Oxy-Fuel (HVOF, JP5000) processes, microstructural defects compromise the reliability of these coatings in high stress applications. Results of this research have shown potential improvements in coating strength due to metallurgical bonding at splat and substrate interface levels, elimination of amorphous phases and macrocracks, and introduction of uniform compressive residual stress for improved fatigue and delamination resistance in tribological applications. For further information use the links below to look through my presentations on HIPing post-treatment of cermet coatings or refer to the list of publications.

Potentials of pos-processing thermal spray coatings – Presentation (Power Point)

Tribological evaluations of HIPed WC-NiCrBSi coatings - Presentation (pdf format)

Tribological evaluations of HIPed WC-Co coatings - Presentation (pdf format)