Plasma-Sprayed Hydroxyapatite Coating for Improved Corrosion Resistance and Bioactivity of Magnesium Alloy
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Plasma-Sprayed Hydroxyapatite Coating for Improved Corrosion Resistance and Bioactivity of Magnesium Alloy Ya Li Gao1 • Yu Liu1 • Xue Ying Song1
Submitted: 5 June 2018 / in revised form: 1 August 2018 Ó ASM International 2018
Abstract In the present study, the corrosion resistance and bioactivity of AZ91HP magnesium alloy were improved by plasma spraying hydroxyapatite (HA) coating. X-ray diffraction measurements indicated that the coating formed amorphous and little b-Ca3 (PO4)2 besides of HA. The corrosion resistance and bioactivity of the coating and magnesium alloy in simulated body fluid were investigated using immersion test. The coating showed lower corrosion rate and better bioactivity than magnesium alloy. The coating significantly improved the hydrophilicity of Mg alloy. The prothrombin time of the coating was 18 s, and the prothrombin time of Mg alloy was 11 s, so the coating had better anticoagulant activity. Keywords bioactivity corrosion resistance hydroxyapatite coating magnesium alloy plasma spraying
Introduction Mg alloys arouse interest of the biomedical fields because of low density, high specific strength and good electromagnetic shielding (Ref 1, 2). It is also an essential element for human metabolism, and owing to its formability, biocompatibility, biodegradability and non-toxicity, magnesium-based alloys are promising candidates as nextgeneration implant materials (Ref 3, 4). Moreover, Mg2? ions trigger bone cell formation and accelerate the healing & Ya Li Gao [email protected] 1
process (Ref 5-7). Despite the attractive range of excellent bulk properties, the poor corrosion resistance is a serious impediment against wider application of Mg alloy as orthopedic implants. Mg alloy is susceptible to corrosion in body fluid, degrading more rapidly compared to the bone formation rate. Therefore, the corrosion resistance of magnesium alloy should be increased for use in the body as a biodegradable implant material (Ref 8-10). HA is a typical bioactivity ceramic material, and its chemical constituents, crystal structure and physicochemical characteristics are similar to those of calcium phosphate of the bone and tooth (Ref 11-13). However, tensile strength and fracture toughness of HA are lower than those of the dense bone, and HA exhibits poor fatigue properties in the physiological environment. As a surface-deposited technology, compared with RFmagnetron sputter-deposited technology, plasma spraying has shown great potential because of having high bond strength, low porosity and inclusion, and improving the surface property of the materials (Ref 14, 15). Plasma spraying HA coating has been carried out largely on titanium alloy, stainless steel and carbon–carbon composites (Ref 16-21). However, there is a few investigation on Mg alloy. The reason is that there have large physical and chemical differences between Mg alloy and HA. With these in mind, in the investigation described here, a study has been made to improve the corrosion resistance and bioactivity of Mg alloy b
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