The microstructure and bio-corrosion behavior of binary Mg-xZn (x ¼ 1.25, 2.5, 4) and ternary Mg-Ca-xZn (x ¼ 1.25, 2.5, 4) alloys have been studied using scanning electron microscopy (SEM), electrochemical, and immersion tests. Microstructure analysis indicated that the binary Mg-Zn alloys are composed of primary a-Mg matrix and Mg 12 Zn 13 phases, while, ternary Mg-Ca-Zn alloys are composed of a-Mg, Mg 2 Ca, and IM1 (Ca 3 Mg x Zn 15Àx ) (4.6 x 12) phases or a-Mg, IM1 and IM3 (Ca 2 Mg 5 Zn 13 ) phases. Electrochemical results showed that Mg-4Zn alloy has lowest corrosion rate among binary alloys. At constant Ca content of 0.8 wt.%, the addition of Zn up to 1.25 wt.% decreased the corrosion rate, while further addition of Zn increased the corrosion rate of ternary alloys. Immersion tests results demonstrated that the formation of Zn oxide layer in binary Mg-Zn alloy and evolution of eutectic phase (a-Mg þ IM1 þ Mg 2 Ca) significantly retard the bio-degradation rate of the ternary alloys.

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Oxidation has been considered as one of the principal disruptive factors in thermal barrier coating systems during service. So, oxidation behavior of thermal barrier coating (TBC) systems with nanostructured and microstructured YSZ coatings was investigated at1000∘Cfor 24 h, 48 h, and 120 h. Air plasma sprayed nano-YSZ coating exhibited a trimodal structure. Microstructural characterization also demonstrated an improved thermally grown oxide scale containing lower spinels in nano-TBC system after 120 h of oxidation. This phenomenon is mainly related to the unique structure of the nano-YSZ coating, which acted as a strong barrier for oxygen diffusion into the TBC system at elevated temperatures. Nearly continues but thinner Al2O3layer formation at the NiCrAlY/nano-YSZ interface was seen, due to lower oxygen infiltration into the system. Under this condition, spinels formation and growth on the Al2O3oxide scale were diminished in nano-TBC system compared to normal TBC system.

Microstructure and corrosion behaviour in simulated body fluid of as‐cast and heat treated Mg–xZn (x = 3 and 6) alloys for different heat treatment times were studied. The results revealed that as‐cast Mg–3Zn alloys consist of Mg12Zn13 phase and α‐Mg matrix, while Mg–6Zn is composed of Mg51Zn20, Mg12Zn13 compounds and α‐Mg matrix. After heat treatment of Mg–6Zn alloy at 340 °C, the Mg51Zn20 phase decomposed to the matrix and Mg12Zn13 while, the microstructure of Mg–3Zn remained unchanged. The results also indicated that heat treatment at 340 °C has little influence on the corrosion behaviour of Mg–3Zn. In contrast, heat treatment improved the corrosion resistance of the Mg–6Zn alloy as the decomposition of the Mg51Zn20 phase decreased micro‐galvanic corrosion. The corrosion resistance of both as‐cast Mg–3Zn and Mg–6Zn alloys marginally improved with increasing heat treatment times.