| As the main bone mineral ingredient, HA(hydroxyapatite) is used as human implants duo to its superior bio-compatibility and bio-activity. In the body, HA exists in the form of c-axis orientation nano-crystalline, but the poor strength and the brittleness limited as the medical implants. The coating is a good choice. Coating the HA film on the Ti-6A1-4V, the composite will have the substrate’ strength and the film’ bio-activity. Given to superior properties of the lower deposited temperature, film’ uniformity, the consistency of the stoichiometric ratio, PLD(the pulsed laser deposition) synthesize widely bio-active films. In fact, HA film have two drawbacks: one is the difference in the HA film and Ti-6Al-4V; another is that HA exist in the form of c-axis orientation in the body. Meanwhile, there is few reports on the oriented HA synthesized by PLD.In this paper, the target is sintered flake mixed powders of HA and CaSiO3, CaSiO3 can reduce HA’CTE(coefficient of thermal expansion), doping Si also affect the orientation of HA. what’more, adding the Y2O3 to target will refine the micro-structure. All of the laser energy, the pressure of oxygen, the substrate’ temperature affect the HA’orientation. The film was characterized by XRD, SEM, EDS, FTIR. The interface bonding strength was tested by nanotest. The bio-activity was studied in SBF and the properties after thermal treatment.The results indicated that the film has the c-axis orientation trend at the 500mJ, the microstructure is more dense at 500mJ than at 300mJ, Moreover, the CO32- doped in the HA ctructure; the orientation of HA changes from random to c-axis orientation with the increasing of oxygen atmosphere; HA film crystallize at 400℃,it crystallizes highly at 600℃ and has the c-axis orientation. Random and c-axis orientation HA film are synthesized at optimum process parameters:300mJ, vacuum,600℃; 300mJ,5Pa, 600℃.The mechanism of process parameters inducing HA orientation is that in the deposition, it causes the OH- concentration gradient, which make the OH- transfer in the HA structure, OH- have a bigger channel along the c-axis in the HA, this induce the film grow along the c-axis; what’ more, the stress generated by the differcece of CTE between substrate and film and the difference in the doped ionic radius has some effect on the HA orientation.The studies on bio-activity and bonding strength with different orientation indicates that the strength of c-axis orientation is higher than the random’, which prove the former bio-activity is better than the latter; EDS show that the content of Ca, p on the spherical particle are higher than on the film, which suggest the ability inducing CaP of CaSiO3 stronger than HA. The bonding strength is connected with the film surface; The film with random fracture in the form of ductile fracture, while the c-axis orientation ductile and brittleness fracture.The properties of HA film after thermal treatment were studied. The crystallization strengthen highly, and appear seriously doping CO32-; After 7d in the SBF, the ingredient have no change after thermal treatment.; After thermal treatment properties of the sample is more stable, its functional group have no change after 7d immersed in SBF; The bonding strength increase from 85mN to 145mN. |
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