In this study, the effects of deep cryogenic treatment (DCT) on the mechanical and tribological properties of AISI D3 tool steel were investigated together with a systematic correlation between their hardness and wear resistance. It was found that conventionally heat treated AISI D3 tool steel samples were significantly hardened via an additional DCT, which was attributed to the more retained austenite elimination, more homogenized carbide distribution and more reduction in carbide size in the samples. As a result, the hardened AISI D3 samples exhibited reductions in their friction and wear during rubbing against alumina and 100Cr6 steel balls under different normal loads due to the effectively hindered removal of surface materials. The results clearly showed that the DCT was an effective way to improve the mechanical and tribological properties of the AISI D3 tool steel samples as the tribological performance of the tool steel samples was significantly influenced by their hardness.

The platinum/ruthenium/nitrogen doped diamond-like carbon (PtRuN-DLC) thin films were deposited on Si substrates via DC magnetron sputtering by varying negative substrate bias. The tribological performance of the PtRuN-DLC films was systematically investigated using ball-on-disc microtribological test. The Raman results showed that the increased negative substrate bias significantly increased the number of sp³ bonds in the PtRuN-DLC films as a result of the increased kinetic energies of impinging ions. The adhesion strength of the PtRuN-DLC films apparently decreased with increased negative substrate bias due to the promoted residual stress in the films. The tribological results clearly revealed that the increased negative substrate bias decreased the friction and wear of the PtRuN-DLC films by improving the sp³ bonded cross-linking structures of the films. It can be concluded that the PtRuN-DLC films could effectively prevent their underlying Si substrates from wear as the negative substrate bias had a significant influence on the tribological properties of the PtRuN-DLC films.

Platinum (Pt) and nitrogen (N) were co-incorporated in diamond-like carbon (DLC) thin films using a magnetron sputtering system to form PtN-DLC thin films for tribological applications. The Pt content in the PtN-DLC films prepared on Si substrates was controlled by varying RF power applied to a Pt target at a fixed N₂ flow rate. The tribological properties of the PtN-DLC films were investigated with respect to the Pt content in the films. The uncoated Si substrate surface tested against a steel ball of 6 mm in diameter had significant abrasive and fatigue wear, while no significant wear was found on the N-DLC coated sample surface, indicating that the N-DLC film effectively prevented its underlying Si substrate from wear. However, the incorporation of Pt in the N-DLC films reduced the wear resistance of the films by degrading sp³-bonded cross-linking structures of the films so that significant wear tracks were found on the surfaces of the PtN-DLC films. Therefore, the increased radio frequency (RF) power applied to the Pt target decreased the wear resistance of the PtN-DLC films as a result of the increased Pt content.

The mechanical and tribological properties of epoxy composites modified with microencapsulated wax lubricant and multi-walled carbon nanotubes (MWCNTs) were investigated. The increased soft microcapsules embedded in the epoxy matrices were responsible for the reduced micro-hardness and Young’s modulus of the epoxy composites. It was found that the friction of the epoxy composites greatly decreased with increased microcapsule content due to combined lubricating effects of the both wax lubricant and MWCNTs. As a result, the wear of the epoxy composites apparently decreased with increased microcapsule content.