Performance of a Direct Bonded Sub-Millimeter Peek Coating for Hydrodynamic Plain Bearings

Despite their superior tribological properties, thick-layer bearing coatings based on polyetheretherketone (PEEK) have up to now not been applied in a very high number of plain bearings for industrial applications. This can at least partly be credited to the high costs and low flexibility associated with the coating process for these materials. At the same time, while thick-layer polytetrafluoroethylene (PTFE) coatings have been successfully applied in industrial plain bearings for around 50 years, thin-layer PTFE coatings today constitute the majority of applications of PTFE in plain bearings. It is therefore reasonable to assume a similar approach for thin-layer PEEK coatings. This article reports the performance of a thin-layer PEEK coating directly applied on a mild steel substrate, with results ranging from first sample test through component tests to application in an actual machine and behavior during realistic operating conditions and induced bearing failure.

Some Hard or Soft Coatings to Protect the Pristine Biometallic Substrates under Fretting-Corrosion Solicitations: What Should Be the Best Solution?

Under tribological conditions in aqueous medium, the contact of materials does involve some degradations of materials. Especially friction under small reciprocal displacement, i.e., fretting corrosion, is occurring; this topic has been highlighted since the 80′s regarding hip implants. Hip prosthesis is assembled from three parts: femoral stem, neck and head. Fretting corrosion or friction corrosion between metallic parts first involves some degradation of the oxides layers. This step is governed by mechanics and it is related to some few minutes. Afterwards the corrosion occurrs enhanced by mechanical degradation. As well focused some oxides and some metallic ions are related to biocompatibility issues. Some strategies are available in order to avoid metal against metal friction and/or fretting. Some hard coatings and some smooth coatings were investigated. The first one is diamond-like carbon (DLC), and the second is a polyetheretherketone (PEEK), polymeric one. The investigations were focused on fretting corrosion solicitations of Ti-6Al-4V vs. Ti-6Al-4V + coating. DLC as a coating delays the corrosion degradation. The PEEK coating does not promote any corrosion degradation of the metallic counter part and more generally any wear.

Thermally Sprayed Porous PEEK Coating for Biomedical Implants

The present study reports the novel results of microstructural and mechanical properties of highly porous Polyetheretherketone (PEEK) coating. PEEK is already considered as a material for biomedical implants. A new kind of approach is proposed for manufacturing of highly porous PEEK coating on a dense PEEK coating for orthopedic implants and successfully implemented to create novel biomimetic porous PEEK coating by means of thermal spray process. To imitate the structure of natural bone, as-sprayed top PEEK coating has porosity of more than 60% vol. and pore sizes of 30-80 μm. Mechanical results of dense PEEK coating show that PEEK coating exhibited good strength, hardness (20 HV0.1) and good bonding strength (15 MPa) with the metal substrate. Thermal sprayed porous PEEK coating that can be used for future implants instead of plasma sprayed titanium coating on dense PEEK implants because porous PEEK improves the bone-implant interface joining compared to plasma-sprayed titanium coating on PEEK.

Antimicrobial Property of Cold-Sprayed Transition Metals-Substituted Hydroxyapatite/PEEK Coating

The antibacterial property of several types of transition metals such as silver, nickel, zinc, and copper substituted hydroxyapatite (HA) composite coatings was investigated against staphylococcus aureus (S. aureus). Microstructural characterization and phase analysis of feedstock powders and as-deposited coatings were carried out using scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX). Transition metals-substituted hydroxyapatite/PEEK coatings were successfully deposited using cold spraying parameters of 10-14 bars at preheated air temperature between 150 and 160 °C. The results indicated that copper substituted hydroxyapatite showed the best antimicrobial property against S. aureus.

Influence of Coating Thickness and Substrate Elasticity on the Tribological Performance of PEEK Coatings

When a material is subjected to repeated sliding contact, a surface fatigue and crack nucleation may occur on its surface. This damage weakens the material and can lead to debris formation. In many practical engineering assemblies, a thin PEEK (poly-ether-ether-ketone) coating is applied to reduce the damage, since PEEK exhibits wear resistance, corrosion resistance self-lubricating capacity and is lightweight. However, little is known about the effect of coating thickness on the plastic deformation, residual stresses and energy dissipation of PEEK when placed under sliding load. Moreover, the effect of substrate rigidity on coating stresses and deformation under sliding load are also under-researched. Having such knowledge is of significant importance in order to reduce damage of engineering parts and extend their lifetime. In this study, the effects of PEEK coating thickness and substrate elasticity were analyzed using a 3D ball-on-flat finite element model as well as experimental analysis using a linear reciprocating tribometer. The experimental tests were performed with samples that incorporated PEEK coatings of various thicknesses on alumina and steel substrates. It was found that under a constant normal load, stresses, strain and energy dissipation were sensitive to both substrate material and coating thickness. It is shown from both simulation and experiment, the optimum combination, within the range the experiments were conducted, for minimizing residual stress and possible fatigue damage was an alumina substrate with 35μm PEEK coating thickness.