Microstructure And Properties Of Pulsed Current Electrodeposited Calcium Phosphate Coatings On The Surface Of AZ91 Alloy Modified By HCPEB

In this paper,calcium phosphate coatings were prepared on AZ91 alloy substrate by pulsed current electrodeposition method at different duty cycle and cycle period.Their corrosion properties in simulated body fluid?SBF?were investigated.The AZ91 alloy were modified by HCPEB?high current pulsed electron beam?with energy density of 6 J/cm².The effect of irradiation time on the morphology,phase and corrosion resistance were investigated.At last,the HCPEB treated surface at different times were coated with calcium phosphate coating by pulsed current electrodeposition method.Their morphology,phase and corrosion resistance were investigated.The experiment results show that as the duty cycle increased,plate-like calcium hydrogen phosphate dihydrate?DCPD?appeared in neddle-like Hydroxyapatite?HAP?under the condition of the cycle period for 1 s.As the cycle period increased,plate-like DCPD appeared in neddle-like HAP under the condition of the duty cycle for 0.10.The calcium phosphate coating which prepared with the optimum condition of 0.10 duty cycle and 1 s cycle period was pure HA,most homogeneous,most ordered,finest to 0.3⁰.4 ?m in diameter and significantly reduced the corrosion current density of AZ91 alloy by two orders of magnitude in the simulated body fluid?SBF?solution according to the electrochemical test.After modified by HCPEB with energy density 6 J/cm²,the surface morphology of AZ91 alloy changed to spherical structure and long cellular structure.The surface hardness of AZ91 alloy increased from 65.6 HV to 75.0 HV.As the irradiation time increased,the content of Al element in ?-Mg increased first and then decrease.After irradiated at 3 times,5 times,10 times,the corrosion potential of AZ91 alloy shifted more to the noble side,the corrosion current density of AZ91 alloy reduced by one order of magnitude.When the irradiation time was more than 10 times,the corrosion resistance of AZ91 alloy decreased due to the decreae of Al element in ?-Mg and Mg₁₇Al₁₂ precipitation.The HCPEB treated surface at different time were coated with calcium phosphate coating by pulsed current electrodeposition method under optimum condition.As the irradiation time increased,plate-like DCPD disappeared in neddle-like HAP.After electrodeposition on untreated AZ91 alloy from 1min to 30 min,the morphology of coatings changed from Strip-like to needle-like.After electrodeposition on HCPEB treated AZ91 alloy at 5 times from 1 min to 30 min,the morphology of coatings changed from granular to reticulate,then to flake-like and finally to needle-like.The electrochemical test and immersion test proved that compared to the calcium phosphate coating on untreated AZ91 alloy,the calcium phosphate coating on HCPEB treated AZ91 alloy showed better corrosion resistance.After immersed in SBF solution for 14 days,the calcium phosphate coating on HCPEB treated AZ91 alloy at 5 times remained intact.Compared to AZ91 alloy,its hydrogen evolution amount was reduced 87.90%.The pH value during the corrosion process was stable at about 7.57.To conclude,the calcium phosphate coating developed on the HCPEB treated AZ91 alloy at 5 times showed the best corrosion resistance.