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High entropy alloys (HEAs), consisting of five or more elements with nearly equal atomic composition with one another (5–35%), are new-generation alloys that have attracted signifi)cant interest since their advent in 2004 because of their unique structural and mechanical properties and thermodynamic and chemical stability. Some characteristics, including high mechanical strength at elevated temperatures, high ductility and fracture toughness at cryo)genic temperatures and high corrosion, erosion and wear resistance, have been demonstrated for HEAs that outperform traditional alloys and superalloys. Laser-cladding (LC) is an additive manufacturing technique that has good feasibility in designing and processing HEAs for advanced structural components and protective coatings. This overview provides a glimpse of recent advances in LC of HEAs in terms of design fundamentals, metallurgical phase and microstructure, specific properties for advanced coating applications and the effect of ceramic particles reinforcement in LC deposition of HEA coatings. [ABSTRACT FROM AUTHOR]

Anodisation with electrochemical cathodic deposition method was employed to modify the surface of Ti implants with a bilayer coating made of Sr- doped titania (Sr-TiO2) and hydroxyapatite doped with magnesium (Mg-HAp). The Mg-HAp/Sr-TiO2 bilayer coating was compared with pure TiO2 and Sr-TiO2 single-layer coating. The Sr incorporation into TiO2 and Mg substitution into HAp strengthened their bioactive properties. The tensile test indicated increase in the mechanical strength of the bilayer coated substrate compared to pure TiO2 substrate. Moreover, the study indicated that the Sr and Mg ions were uniformly incorporated into the Mg-HAp/Sr-TiO2 bilayer coating with significantly higher roughness and hydrophilicity compared to the control. In vitro studies with osteoblasts cells had a superior response to the Mg-HAp/Sr-TiO2 bilayer surface. It was found that a bilayer Mg-HAp/Sr-TiO2 coating on Ti implants promotes bioactivity and has superior adhesion strength necessary for osseointegration and bone healing. [ABSTRACT FROM AUTHOR]

The wide application of magnesium alloys as biodegradable implant materials is limited because of their fast degradation rate. Hydroxyapatite (HA) coating can reduce the degradation rate of Mg alloys and improve the biological activity of Mg alloys, and has the ability of bone induction and bone conduction. The preparation of HA coating on the surface of degradable Mg alloys can improve the existing problems, to a certain extent. This paper reviewed different preparation methods of HA coatings on biodegradable Mg alloys, and their effects on magnesium alloys' degradation, biocompatibility, and osteogenic properties. However, no coating prepared can meet the above requirements. There was a lack of systematic research on the degradation of coating samples in vivo, and the osteogenic performance. Therefore, future research can focus on combining existing coating preparation technology and complementary advantages to develop new coating preparation techniques, to obtain more balanced coatings. Second, further study on the metabolic mechanism of HA-coated Mg alloys in vivo can help to predict its degradation behavior, and finally achieve controllable degradation, and further promote the study of the osteogenic effect of HA-coated Mg alloys in vivo. [ABSTRACT FROM AUTHOR]