Cold spray deposition of polycarbonate on the various substrates has been investigated. The polycarbonate particles are sieved and accelerated at elevated temperature in air through a DeLaval type nozzle, and are deposited on the metallic and ceramic substrates. The influences of the particle size, the gas temperature, the thermal conductivity and surface roughness of substrate on the deposition process are studied. As a result, the continuous deposits are formed on the metallic substrate. The powder sieved below 300 μm shows better deposition efficiency. Thin film of melted polycarbonate has been formed on the surface of substrate to act as a bonding layer, and its crystalline structure is changed to be amorphous, which is the more stable state for the polycarbonate. The coating seems to be better when the thermal conductivity of metallic substrate is low. For the ceramic substrates, there is no deposition whatever was the thermal conductivity.

Hydroxyapatite (HA) is preferred for its ability to interact with living bone, resulting in improvements of implant fixation and faster bone healing. In this study, a small amount of silicon dioxide (~ 2wt%) was introduced into HA slurry which was subsequently spray-dried into powder. A silicon modified HA coating was then deposited onto Ti-6Al-4V alloy substrates by atmospheric plasma spraying technology. Scanning electron microscopy (SEM), X-ray diffraction and X-ray photoelectron spectrometry, and Raman spectrometry were employed to investigate the surface chemistry that would directly influence bone forming cell proliferation. Additionally, the adhesive bonding strength of the as-sprayed coatings were specified measured using a universal testing system. The fracture surfaces after tensile test were also investigated by SEM.

HVOF has the potential to produce Hydroxyapatite HA (Bio-ceramic) coatings based on its experience with other sprayed ceramic materials. This technique should offer mechanical and biological results comparable to other thermal spraying processes such as plasma spray currently FDA approved for HA deposition. Deposition of HA via HVOF is a new venture especially using the Sulzer Metco Diamond Jet (DJ) process, hence the aim of this paper. In this research, a Design of Experiment (DOE) model as developed to optimize the HVOF process for the deposition of HA. Five parameters (factors) were researched over two levels namely: oxygen flow rate, propylene flow rate, air flow rate, spray distance and powder flow rate. Coating crystallinity and purity were measured as the responses to the factors used. The research showed that: propylene, air flow rate, spray distance and powder feed rate had the largest effect on the responses and the study aimed to find the desired optimised settings. This research found crystallinity and purity values of 93.8% and 99.8% respectively for a set of HVOF parameters which were improved findings compared to the crystallinity and purity of 87.6 % and 99.4 % respectively found using the FDA approved Plasma thermal spray process. Hence a new technique for HA deposition now exists using the DJ HVOF facility. Future research aims to evaluate the biological response to these coatings through in vitro tests.