Abstract Hydroxyapatite (HA) was plasma sprayed onto titanium alloy substrates. One set of samples had a crystalline content of 25%, the other set, 30%. The coatings were then subjected to CO2 laser treatments at different power levels and scanning rates while surface temperatures ware monitored with a pyrometer. XRD analysis verified the crystallinity of HA and the content of amorphous calcium phosphate as well as foreign phases. Optical microscopy revealed the microstructure and depth of the laser modified zone.

Abstract As part of a characterization and mechanical research about hydroxyapatite (HA) plasma deposits for hip prosthesis, we addressed the problem of determining their crystallinity. A traditional normalization method employed by several laboratories is based on X-ray diffraction by a powder mixture of the investigated HA sample with a standard of crystalline powder, namely Al 2 O 3 . This method is quite unsatisfactory, as very often delivers unreasonable results. In order to overcome these difficulties we investigated some new methods for determining the crystallinity of HA sample, which are based on X-ray diffraction. All these methods provide reasonable results.

Abstract The attractive bioactive properties of HA are significantly reduced upon plasma spraying because of the phase transformation that accompanied the deposition process. One major factor that influence the extent to which the transformation occur appears to be the morphology and physical states of the HA raw powders. This paper reports the study on the influence of powder morphology and property on the fracture behaviour and tensile adhesive strength of plasma sprayed HA coatings. Three types of powders were used in the study; calcined HA (CHA), spray dried HA (SDHA) and flame spheroidised HA (SHA). The particle size range of 53 - 75 μm was employed for all 3 types of powders to effect an accurate comparison of the powders. Results show that the cohesive bond strength of the SHA coating was the highest because of the denser microstructure created by well-formed lamella splats. A correspondingly lower bond strength was recorded with less coherent coatings generated by agglomerated CHA and SDHA powders.

Abstract One cause of aseptic loosening of total hip replacement (THR) results from the hard polymetylmethacrylate (PMMA) bone cement debris embedded within some of acetabular cups [1]. To prevent this failure, PMMA can be replaced by a titanium coating with a specific roughness to promote the bone bonding. In this work, inert and atmospheric plasma spraying was used to coat Ti.6A1.4V implants with titanium.] In order to evaluate the effect of the deposition process on the coating corrosion resistance, different electrochemical techniques were implemented in physiological (i. e., Ringer) and in acidic solutions. Results show that the spraying parameters and the coating morphology affect the corrosion behaviour. Thus, if the reactivity is not affected by the pH evolution, the pitting sensitivity depends on the process. It was found that coatings deposited under inert gas are free of oxides and dense, even when the atmosphere contains some hydrogen. In that case a significant improvement of the intrinsic localized corrosion resistance is observed versus deposits obtained using atmospheric plasma spraying.

Abstract Thermal plasma spraying is a suitable technique for hydroxyapatite [HA, Ca 10 (P0 4 ) 6 (OH) 2 ] coating preparation. Suspension Plasma Spraying (SPS) is a newly developed process based on a suspension of fine (<10 μm) or even ultrafine (<100 μm) powders, axially fed into the RF plasma through an atomization probe. The atomization of the suspension results in microdroplets (20 μm in size). They are flash dried, melted and finally impacted onto the substrate to solidify and build the coating. The aqueous suspension of HA is chemically synthesized. Our experiments included variations of the plasma gas composition (Ar/O 2 , Ar/H 2 ), the plasma deposition reactor pressure. Characterizations techniques (e.g. X-ray diffraction, scanning electron microscope and transmission electron microscope) were applied to resultant SPS HA coatings which possessed good crystallinity and about 3% weight α-TCP and lime. The texture examination has shown that preferential crystal orientation followed the (001) Miller's plane family. SPS by RF induction plasma has proved to be a reliable process for the production of thick (200 μm) HA coatings with high deposition rate (>150 μm/min).