[Show abstract][Hide abstract] ABSTRACT: A Cr2AlC coating was deposited on a β–γ TiAl alloy. Isothermal oxidation tests at 700°C and 800°C, and thermocyclic oxidation at 800°C were performed in air. The results indicated that serious oxidation occurred on the bare alloy. Thick non-protective oxide scales consisting of mixed TiO2+α-Al2O3 layers formed on the alloy surface. The coated specimens exhibited much better oxidation behaviour by forming an Al-rich oxide scale on the coating surface during the initial stages of oxidation. This scale acts as diffusion barrier by effectively blocking the ingress of oxygen, and effectively protects the coated alloys from further oxidation.
[Show abstract][Hide abstract] ABSTRACT: An ∼ 5 µm Cr2AlC coating was synthesized on near-α titanium alloy Ti6242 using an industrially sized magnetron sputtering coater. Isothermal oxidation at 700 °C and 800 °C, and cyclic oxidation at 700 °C of the bare alloys and coated specimens were investigated in air. The results indicated that the Ti6242 alloy faced serious oxidation problems at 700 °C and 800 °C. Repeated formation and spallation of the multilayered oxide scale on the Ti6242 alloy occurred during oxidation testing. The coated specimens exhibited much better oxidation behaviour as compared to the bare alloy. A continuous Al-rich oxide scale formed on the coating surface during the initial oxidation stages. The oxide scale and coating itself acted as diffusion barriers blocking the further ingress of oxygen and protected the substrate alloy from oxidation. The oxidation mechanisms of the bare alloy and the coated specimens were investigated based on the experimental results.
[Show abstract][Hide abstract] ABSTRACT: The influence of Si and N in Ge2Sb2Te5 (space group ) on structure and phase stability thereof was studied experimentally by thin film growth and characterization as well as theoretically by ab initio calculations. It was found that Si and N most probably accumulate in the amorphous matrix embedding Ge2Sb2Te5 grains. The incorporation of Si and N in these samples causes an increase of the crystallization temperature and the formation of finer grains. N is more efficient in increasing the crystallization temperature and in reducing the grain size than Si which can be understood based on the bonding analysis. The incorporation of both Si and N in Ge2Sb2Te5 is energetically unfavourable, leading to finer grains and larger crystallization temperatures. While in the case of Si additions no significant changes in bonding are observed, N additions appear to enable the formation of strong Te–N bonds in the amorphous matrix, which are shown to be almost twice as strong as the strongest bonds in unalloyed Ge2Sb2Te5.