New advanced polymeric biomaterials such as implantable poly(etheretherketone) (PEEK) are changing the face of the implantable medical device industry. Due to its bioactive behavior in vivo, hydroxyapatite (HA) coatings are used to improve the bone growth and to repair around metallic implant. The objective of this work is to study the feasibility of plasma sprayed hydroxyapatite coating on PEEK material. Different PEEK (unfilled and composite) specimens were successfully coated with a 150 µm thick coating. Chemical and crystallographic compositions, adhesions and microstructures of HA coatings on PEEK and on Ti-6Al-4V were compared. The results showed that the structure of HA coatings were appreciably equivalent. Mechanical tests showed that the plasma spraying process did not severely degrade the initial properties of the PEEK substrate.

Porosity is a key feature of thermally-sprayed coating microstructure. Porosity is made of pores and cracks of various orientations. Both pores and cracks can be intralamellar or interlamellar due to coating build-up which leads to lamellae from impinging of droplets. Pores are interconnected with cracks, which results in a 3-dimensional porosity network. Direct observation of this network is intricate and remains somewhat limited. A 3-dimensional simulation of this network was therefore developed in this work based on the building-up of objects which simulated the lamellae in the sprayed microstructure. These objects were constructed from morphological measurements using confocal microscopy of actual lamellae, i.e. “splats”, obtained from “linescan”-typed plasma-sprayed experiments. This simulation, in the lamella building-up, involves randomly cracks and pores the characteristics of which (i.e. content, orientation, size, …) were determined from thorough quantitative image analysis of cross-section plasma-sprayed alumina microstructures. Using 3-dimensional images resulting from the simulation, finite element calculations were performed to study dielectric properties of plasma-sprayed alumina as a function of porosity. The influence of anisotropy is discussed in particular and calculated values compared to experimental values.

Pure alumina coating obtained by thermal spraying can find applications as electrical insulating layer. Thermally-sprayed ceramic coatings exhibit a complex lamellar structure with a network of interconnected pores, inter-lamellar and intra-lamellar cracks. In this work, the influence of the microstructure on electric properties for plasma-sprayed alumina coatings was investigated. Coatings have been sprayed with different pressures and gases using a CAPS (‘Controlled Atmosphere Plasma Spraying’) as well as different alumina feedstock powders. Detailed quantitative image analysis of cross-section views allowed to select six microstructures with different porosity levels and cracks orientation distributions. In order to assess the behaviour of the electrical insulation and the influence of local defects on electric properties, the so-called Scanning Electron Microscope Mirror Effect (SEMME) method has been applied on outer surfaces and on cross-sections of the different selected alumina coatings. This method, originally developed to study the ability of a bulk insulating material in trapping of charges from an electron beam irradiation in a SEM, revealed to be successfully feasible for porous materials such as thermally-sprayed ceramic coatings. It has been shown that cracks orientation modified both propagation and trapping of charges and therefore the electric properties of plasma-sprayed alumina coatings.

Crevice corrosion of metal/metal contacts in piping assemblies is a key issue for the design and the manufacturing of marine components. In this work, ceramic coatings onto alloy 625 were obtained using multi-processing CAPS facilities (Controlled Atmosphere Plasma Spraying). These coatings were sprayed in the CAPS chamber using air plasma spraying (APS, air at 100 kPa) or using high-pressure plasma spraying (HPPS, argon at 250 kPa) to achieve different coating microstructures and porosity levels. This allowed to investigate the corrosion behaviour in natural sea water of metal/ceramic contacts with different coating systems. Pure alumina or alumina-titania coatings with or without thermally-sprayed alloy 625 bond-coat were tested. Post-treatments like sealing of pores using epoxy resin were also achieved to study the resulting corrosion protection enhancement. Immersion and potentiostatic tests at +300 mV vs. SCE (Standard Calomel Electrode) tests were carried out in natural sea water at different temperature up to 60°C to expose specimens to the most severe working parameters. A beneficial protective effect of ceramic-coated alloy 625 has been clearly evidenced. Further investigations were performed using light microscopy and scanning electron microscopy to assess the corrosion behaviour and mechanical soundness of ceramic coated specimens which resulted in the determining of relevant technological solutions to prevent the risk of corrosion.

Thermal plasma spray processes with their various operating parameters can be considered as flexible technique to carry out appropriate ceramics coatings. This work deals with plasma spraying of several ceramics powders (hydroxyapatite (HA), Al 2 O 3 -TiO 2 , Al 2 O 3 , ZrO 2 -Y 2 O 3 (YSZ) and Cr 2 O 3 ) with suitable parameters using a CAPS system ("Controlled Atmosphere Plasma Spraying"). The HPPS (High Pressure Plasma Spraying), APS (Air Plasma Spraying) and IPS (Inert Plasma Spraying) modes were applied in order to obtain the suitable microstructure. The microstructures and phase compositions allowed to establish that surrounding high-pressure in the CAPS chamber is leading to a good heating of the powder and a good quality for the coatings.