The present work addresses the performance of polycaprolactone (PCL) coating on fluoride treated (MgF2) biodegradable ZK60 magnesium alloy (Mg) for biomedical application. MgF2 conversion layer was first produced by immersing Mg alloy substrate in hydrofluoric acid solution. The outer PCL coating was then prepared using dip coating technique. Morphology, elements profile, phase structure, roughness, mechanical properties, invitro corrosion, and biocompatibility of duplex MgF2/PCL coating were then characterized and compared to those of fluoride coated and uncoated Mg samples. The invivo degradation behavior and biocompatibility of duplex MgF2/PCL coating with respect to ZK60 Mg alloy were also studied using rabbit model for 2 weeks. SEM and TEM analysis showed that the duplex coating was uniform and comprised of porous PCL film (~3.3 μm) as upper layer with compact MgF2 (~2.2 μm) as inner layer. No significant change in microhardness was found on duplex coating compared with uncoated ZK60 Mg alloy. The duplex coating showed improved invitro corrosion resistance than single layered MgF2 or uncoated alloy samples. The duplex coating also resulted in better cell viability, cell adhesion, and cell proliferation compared to fluoride coated or uncoated alloy. Preliminary invivo studies indicated that duplex MgF2/PCL coating reduced the degradation rate of ZK60 Mg alloy and exhibited good biocompatibility. These results suggested that duplex MgF2/PCL coating on magnesium alloy might have great potential for orthopedic applications.

Tungsten carbide (WC) in Ni-based powders is a promising candidate for laser-based additive manufacturing because WC is an extremely hard material, whereas Ni is tough and weldable. However, WC particles that are directly exposed to a laser beam can be degraded or disintegrated into tungsten and carbon as a result of excess energy. In contrast, particles in the melt pool are relatively stable. In this study, the direct energy deposition method was used with irregular and spherical WC particles in metal powder. Irregular WC particles were found to be more directly affected by laser irradiation. To explain the effects of WC particle shapes on direct laser damage, a finitepoint calculation was performed to estimate the sinking time in the melt pool. The rectangular shape particles a longer sinking time depending on the rotation angle, whereas the spherical particles sank uniformly based on the difference in the effective area of resistance.

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