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A strategy of suppressing the fast degradation behaviour of Mg-based biomaterials by the introduction of one of Mg degradation products Mg(OH) 2 was proposed according to the following degradation mechanism, Mg + 2H 2 O ⇋ Mg(OH) 2  + H 2 ↑. Specifically, Mg(OH) 2 submicron particles were mixed into poly (L-lactic acid) (PLLA) to synthesize a composite coating onto hydrofluoric acid-pretreated Mg-Nd-Zn-Zr alloy. The in vitro degradation investigations showed that the addition of Mg(OH) 2 particles not only slowed down the corrosion of Mg matrix, but also retarded the formation of gas pockets underneath the polymer coating. Correspondingly, cytocompatibility results exhibited significant improvement of proliferation of endothelial cells, and further insights was gained into the mechanisms how the introduction of Mg(OH) 2 particles into PLLA coating affected the magnesium alloy degradation and cytocompatibility. The present study provided a promising surface modification strategy to tailor the degradation behaviour of Mg-based biomaterials., Competing Interests: The authors declare no competing financial interests.

• CoCrFeMoNi alloys were prepared by vacuum arc-melting from pure elements. • The validity of new PHACOMP method for high-entropy alloys are verified. • New PHACOMP method can be used to evaluate thermal stability of high-entropy alloy. • The designed CoCrFeMoNi high-entropy alloys show competitive corrosion resistance with commercial alloy. [Display omitted] Various methods can be used to predict the phase composition of conventional alloys. However, it is relatively difficult to predict high-entropy alloys (HEAs) owing to their complexity. There remain many challenges in designing HEAs with desirable properties. In this study, two strategies were applied to design corrosion-resistant non-equal-molar CoCrFeMoNi HEAs with a single phase. The two strategies were prediction for valence electron concentration dependent structural behavior to evaluate the matrix of HEAs, and average d -orbital energy level ( M ̅ d) that was initially used to predict precipitation in superalloys under different temperatures. The validity of these two approaches was determined by thermal stability. The corrosion behaviors of the designed HEAs were investigated by polarization tests. In conclusion, the phase compositions of CoCrFeMoNi HEAs were predicted using a combination of the two approaches. The corrosion resistance was also competitive compared to that of Hastelloy C276. This research can provide a reference for the future development of corrosion-resistant HEAs with a single phase. [ABSTRACT FROM AUTHOR]

Abstract The Hf 0.5 Nb 0.5 Ta 0.5 Ti 1.5 Zr refractory high-entropy alloy with excellent corrosion resistance in the 3.5 wt% NaCl solution is identified in this work. This refractory high-entropy alloy exhibits much better general corrosion resistance than that of the 316L stainless steel, due to its corrosion current density being about one fifth of that in the latter. Meanwhile, the pitting potential of Hf 0.5 Nb 0.5 Ta 0.5 Ti 1.5 Zr reaches an unusually high value of +8.36 V, much higher than that of reported high-entropy alloys. The superior passivity of Hf 0.5 Nb 0.5 Ta 0.5 Ti 1.5 Zr is accredited to the formation of a single-phase solid solution containing high amount of homogenously distributed passivity-promoting elements, and also the existence of metallic Ta and OH− species in the passive film, which contribute to the high immunity to passive film breakdown. Highlights • Hf 0.5 Nb 0.5 Ta 0.5 Ti 1.5 Zr contains finely distributed passivity-promoting elements. • Hf 0.5 Nb 0.5 Ta 0.5 Ti 1.5 Zr exhibits better general corrosion resistance than 316L SS. • E pit of Hf 0.5 Nb 0.5 Ta 0.5 Ti 1.5 Zr reaches +8.36 V, beating all other reported RHEAs. [ABSTRACT FROM AUTHOR]

The state-of-the-art metallic biomaterials are 316L, CoCrMo and Ti6Al4V but they all suffer from known issues relating to biocompatibility, wear resistance and corrosion resistance. Therefore, there is always the motivation to identify novel superior metallic biomaterials to 316L, CoCrMo and Ti6Al4V. The concept of refractory high-entropy alloys (RHEAs) provides an interesting research direction towards developing novel metallic biomaterials, initially because RHEAs consist of purely biocompatible elements, but a systematic study of the performance of RHEAs targeting biomedical applications, while comparing to that of the state-of-the-art 316L, CoCrMo and Ti6Al4V, was not existing before and constitutes the theme of the current work. Two exemplary RHEAs that are studied in detail in this work, TiZrTaHfNb and Ti 1.5 ZrTa 0.5 Hf 0.5 Nb 0.5 , show highly promising characteristics as novel superior metallic biomaterials in that they possess a desirable combination of wear resistance, wettability and pitting and general corrosion resistance, outperforming 316L, CoCrMo and Ti6Al4V almost in all these important aspects. In addition, it is also shown in this work that how appropriate alloying in RHEAs can be utilized to fine-tune their performance as better metallic biomaterials, such as the correlation between lattice strain and corrosion resistance. Image 1 • As-cast TiZrTaHfNb and Ti 1.5 ZrTa 0.5 Hf 0.5 Nb 0.5 were composed of a single BBC phase. • Ti 1.5 ZrTa 0.5 Hf 0.5 Nb 0.5 showed lower lattice strain than TiZrTaHfNb. • RHEAs exhibited higher H and E ratios compared to 316L, CoCrMo and Ti6Al4V. • TiZrTaHfNb and Ti 1.5 ZrTa 0.5 Hf 0.5 Nb 0.5 revealed no pitting effect. • Ti 1.5 ZrTa 0.5 Hf 0.5 Nb 0.5 has more resistance of barrier oxide than TiZrTaHfNb. [ABSTRACT FROM AUTHOR]