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Hydroxyapatite(HA)biological ceramic material has excellent biological activity and biocompatibility, but HA is too weakness for sintering intensity and large brittle to meet clinical use requirement. In recent years, people have been developing material surface treatment technology to coat HA biological ceramic material into substrate surface of titanium alloy of metal to form HA biological ceramic coating material. HA biological ceramic coating material can play advantages combined the biological ceramic material and titanium alloy material and overcome the shortcomings of their respective. It can better meet the need of clinical application.

1. The artificial joint surface vacuum plasma arc spraying Ti, HA coating. Ti or its alloy in the substrate of sedimentary plasma spraying titanium (Ti), hydroxyapatite (HA) coating have been used in the clinical application. Plasma arc spraying is a high temperature process. There will be some complicated physical and chemical change while spraying powder . Comparing its spraying powder, Plasma arc spraying HA coating will change structure and composition, and lead to decrease the crystallinity of coating . In the higher than 500degree environment, Ti is easily react with O2, H2, and N2 and CO2 . Because of the very high temperature of plasma arc jet (as high as 10000 degree), Ti will react with the surrounding atmosphere when plasma arc spraying, the Reaction products produced from spraying created will often reduce the ductility of coating, and lead to material produces to crack.

2. Comparing atmospheric plasma arc spraying, Vacuum plasma arc spraying has the features of jet speed and lower temperature and controllable atmosphere of spraying room and so on. The coating is rather dense with low level oxygen ,its composition approaches powder . Figure 1 for vacuum plasma spraying equipment. Applying vacuum Plasma spraying technology can get a coating good performance of Ti and HA.

Vacuum plasma arc spraying not ready

3. Comparing the Ti, HA coating in the Ti-6 Al-4V substrate by vacuum and atmospheric plasma arc spraying, we found Ti coating sprayed in atmosphere is more serious for oxidation. There are a lot of TiO2 and TiO among the coating, but in the vacuum coating, the oxidation can avoid. The oxidation affects the union of coating and alloy substrate.The bond strength of atmospheric spraying (APS) Ti coating and the base is 37 MPa, but the strength combination of vacuum coating (VPS) and Ti coating is 60 MPa. Compared with the original powder, plasma spraying HA coating contain some amorphous and new phase, such as CaO and Ca3 (PO4). Amorphous phase formation is mainly due to high temperature melting in the particles in the basal spraying on caused by reports; And CaO and Ca3 (PO4) 2 and other new phase is from spraying process HA decomposition. Vacuum spray coating of amorphous and HA new phase significantly reduced as this mainly thanks to VPS spraying low flame flow temperature. Results show that APS HA, the crystallinity of coating is only 42%, but the crystallinity of VPS HA coating is more than 60%. It can meet requirements of clinical implanted on the coating of crystallinity. Vacuum plasma spraying Ti-HA coating artificial hip actual parts ( as the below picture). Already spraying artificial hip implant about 7000 pieces.

Artificial hip coated with Ti-HA by vacuum plasma spray machine 

4. HA matrix composite coating Using the plasma arc spraying technology in the Ti-6 Al-4 V alloy substrate to produce Ti, HA HA/TiO2, HA/ZrO2 and so on composite coating can effectively improve the union between coating and the substrate. Bonding strength analysis shows that the combination of coating can be improved blended with metal or ceramic composition etc in HA coating .For example, if HA/ZrO2 composite coating, mix with ZrO2 = 60% of the composite coatings ,the strength will be a times higher than pure HA coating. With the improvement of strength, mainly because of doping thing to ease the coating substrate and the hot coefficient of expansion between the mismatch, reducing the thermal expansion coefficient mismatch lead to the remnants of the thermal stress in the coating and matrix interface in concentration. In addition, the combination of doping thing small body high strength is also composite coating to improve the bonding strength. 

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