This study assesses the influence of atmospheric plasma spraying parameters on splat stacking and porosity formation in bioglass coatings prepared from commercial powders. Coating samples were deposited on stainless steel substrates using spraying parameters established through numerical simulations. Different Ar-H 2 mixtures were used as the forming gas, and plasma current and spraying distance were varied. Coating microstructure and phase composition were determined by SEM and XRD analysis. Although numerical simulations for each parameter set predicted a suitable Sommerfeld number for proper splat stacking, Na 2 O and P 2 O 5 volatilization occurred during spraying, promoting the formation of porosity in the coatings. Denser coatings were obtained, however, by adjusting the gas mixture ratio, plasma current, and spraying distance such that enthalpy of the plasma jet is sufficient to overcome the glass transition temperature of the powder and at the same time avoid the evaporation of volatile oxides.

In this study, bioactive glass powders were synthesized from four different types of oxides (SiO 2 , P 2 O 5 , CaO and MgO). These oxides were mixed, melted, milled and sieved to produce powders with two chemical compositions of the 31SiO 2 -11P 2 O 5 -(58-x)CaO-xMgO system. The powders were plasma sprayed onto AISI 316L stainless steel and Ti6Al4V titanium alloy substrates using a F4MB Sulzer Metco gun. The physical and mechanical properties of coatings, as well as their bioactivity were evaluated. The bioactivity tests were carried out exposing the surface of coatings to simulated body fluid (SBF) during 1, 9 and 15 days. The thickness and hardness of apatite layer produced on the surface of each coating during bioactivity tests were evaluated. The results indicate that the thickness of apatite layer formed during 15 days in SBF is between 31 and 51 µm and its hardness is between 1.5 and 1.9 GPa according to the chemical composition of feed stock powder used to manufacture the coatings. Additionally, the harness of bioglass coatings decreased around 26% after to expose them to SBF.

Atmospheric plasma and oxy-acetylene flame were used to spray alumina-titania micrometer sized particles with respectively 13 wt.% and 45 wt.% of TiO 2 (AT-13 and AT-45). Plasma spraying was also used to spray nanometer-sized- agglomerated particles (AT-13). The enthalpy of spray guns was varied to achieve coatings with different phases and structural characteristics. The influence of the different structural characteristics and the phases of coatings on their hardness and tribological behavior was then studied. The wear resistance was determined by dry elastic contact between an alumina ball, 6 mm in diameter, and the polished coated discs. The ball was moved at a linear speed of 0.1 m/s under a load of 5 N during 20,000 cycles. Drilling tests between a steel drill bit, 12.5 mm in diameter, and the coating surface were also carried out in order to determine the wear resistance under plastic contact. The wear test results showed that AT-13 coatings were more resistant than the AT-45 ones, which was due to the presence of α and γ alumina, phases presenting a high mechanical resistance. On the contrary the resistance of AT-45 coatings, consisting of Al 2 TiO 5 and Al 6 Ti 2 O 13 brittle phases of low hardness, was poorer. Under elastic contact the reduction of the wear resistance of coatings elaborated by flame spraying was not obvious, but under plastic contact the plasma sprayed coatings were more resistant than those deposited by oxy-acetylene flame.

Al 2 O 3 -13 % wt TiO 2 thermal sprayed coatings exhibit good wear resistance under tribological conditions, thanks to their high toughness. Alumina/titania coatings with two different structures, and similar titania content, have been elaborated by atmospheric plasma spraying (APS). The aim was to compare the effect of the structure on hardness and wear resistance. As feedstocks were used Al 2 O 3 -13 wt % TiO 2 powders with two different structures: micrometer sized ones, with two size distributions (5 – 30 μm and 15 – 45 μm), and agglomerated nano-meter sized particles (grain diameters between 200 to 500 nm) with a size distribution between 10 and 45 μm. Coatings were sprayed onto low carbon steel (XC38) substrates with several spray parameters, the plasma forming gas used being mixtures of Ar and H 2 (45/15 and 53/17 SLM, respectively). Results show that, with the tribological conditions used in this study, the wear resistance of coatings principally depends of their hardness and not very much on the starting powder morphologies.

In this work, the influence of microstructure, hardness, elastic modulus, and fracture toughness on the tribological behavior of flame-sprayed Al 2 O 3 -TiO 2 and WC-NiFeCr coatings is investigated. Fracture toughness was found to be the most influential property, with higher toughness corresponding to greater wear resistance. This relationship, however, is verified only up to the point where the applied stresses cause detachment of particles from the surface. Hardness emerged as a less dominant factor than fracture toughness, elastic modulus, and porosity due to the fact that ceramic coatings, despite their high hardness, have low relative wear resistance.

In the present work, the effect of coating toughness on the wear resistance of alumina-titania coatings was studied. Two parameters were modified: Al 2 O 3 -TiO 2 ratio and particle size distribution. Coatings were obtained by atmospheric plasma spraying on a carbon steel disc. Coating toughness was measured by indentation tests, while wear resistance was determined by ball-on-disc measurements. The results show that coatings with higher toughness exhibit better wear resistance.