| High corrosion rate in physiological environment of body is the major drawback of magnesium alloys for their application as biodegradable orthopedic implants. Bulk metallic glasses are relative newcomers in the field of biomaterials but they exhibit excellent properties desired for versatile implant application, such as Zr60Ti6Cu19Fe5Al10 BMGs. The aim of this presentation is to deposit Zr60Ti6Cu19Fe5Al10 amorphous layer on AZ31B magnesium alloy by laser cladding. The microstructure, thermal stability, hardness, wear resistance of coating were studied in this dissertation by using scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimeter (DSC) and micro-sclerometer. The corrosion behavior and biological activity of coating were also studied by electrochemical corrosion polarization test and immersion test. The results can be summarized as fllowing:(1) A pore and crack-free coating with metallurgical bonding to the substrate was obtained. The clad layer was mainly composed of amorphous phase and intermetallic compounds.(2) The hardness values measured for the amorphous were fairly uniform ranging between 450HV and 680HV, which is obviously higher than those of the composite phases (about 100HV) and the substrate (about 60HV). The wear resistance of magnesium were significantly improved by cladding it with the amorphous coating.(3) Electrochemical anodic polarization test in Hank's solution showed that the corrosion potential Ecorr of the coated specimens were -1.18V which was shifted to less negative values than that of as-received alloy (-1.42V), the cathodic current icorr of the laser cladded specimens was only about 1/3 of the substance, indicating the coated specimen exhibited higher corrosion resistance than the uncoated specimen.(4) The in vitro evaluation of the specimen were immered Hank's solution, the repreciatied phases were formed on the coatings and nearly cover the whole amorphous surface after immersed 4 days. The density, volume and crystallnnity of reprecipiated phase on the amorphous coating are all higher than those of reprecipiated phase on the Magnesium alloy substance.The laser cladding Zr60Ti6Cu19Fe5Al10 amorphous layer show much better biocompatibility in vitro than AZ31B magnesium alloy. |
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