Papers by Author: Dong Ya Huang

Abstract: The isothermal initial oxidation kinetics of Zr55Cu30Al10Ni5 bulk metallic glass in glassy state (lower than Tg = 685K) and in surpercooled liquid state (Tg = 685 K < T < Tx=774 K) is investigated under dry air by thermogravimetric method in short-term stage (for 1.5 hours). A protective parabolic law is followed in glassy state, except at 573 K where a linear law is followed. The self-limiting oxidation kinetics evolves from a short linear stage to a steady mild growth stage in supercooled liquid state at 723 K, which is induced mainly by crystallization and by the fast growth of dense scale. The growth of the scale is dominated by the formation of tetragonal-ZrO2 (t- ZrO2) in the range of 623 K - 673 K in glassy state for 1.5 hours. The activation energy of oxidation is mainly piloted by the diffusion of oxygen ions.

Abstract: Oxidation kinetic of a Zr55Cu30Al10Ni5 bulk metallic glass (BMG) and its crystalline counterpart were studied under dry artificial air (20% of O2 and 80% of N2) at 673 K by thermogravimetry analysis (TGA) method. According to TGA profiles, the oxidation kinetic in both amorphous and crystalline states followed a protective parabolic law. However, the oxidation rates for the amorphous alloy were obviously higher than those for the crystalline alloy. Pseudo-grazing incident X-Ray diffraction (GIXRD) has been carried out to identify the oxides nature and their crystalline structure. Tetragonal-ZrO2 dominated the oxide scale formed on both alloys (BMG and crystalline) at T = 673 K; meanwhile, a slight amount of Cu was detected on the oxide surface of studied BMG alloy. The atomic diffusion mechanism was investigated using a two-stage oxidation treatment to study oxide scale growth kinetics. The studied specimens were oxidized firstly under dry artificial air and then under 18O2 isotopic tracer gas for 1.5 hours respectively at 673 K. The evident solute penetration zone and ion diffusion characteristic through the oxide scale were determined by Cs+ secondary ion mass spectrometry (SIMS) depth profile. The results showed the mechanism of the oxide layer formation of both alloys was not only due to Oxygen ions diffusion from oxide surface to interior scale, but also to an outward diffusion of Zirconium ions from substrate to oxide layer and the ZrO2 oxide growth seemed to occur at the oxide/gas interface in our studied case.

Abstract: The isothermal oxidation behavior of Zr58Nb3Cu16Ni13Al10 bulk metallic glass (BMG) under dry air in the glassy state and the supercooled liquid state (SLS) was studied by the thermogravimetric method. The oxidation rate and thickness growth speed in the SLS were both hugely higher than in the glassy state. The oxidation kinetics of BMG in both states for 1.5 hours was different, the parabolic law was followed in the glassy state at 300°C and 350°C, contrarily the linear law was followed in SLS at 400 °C. After the oxidation for 126 hours in SLS, the oxidation kinetics possessed two stages, the linear stage and the parabolic stage. The diffusion of the Cu2+ ion and CuZr intermetallic alloys were detected by GIXRD.