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To reveal the effects of water vapor on the oxidation mechanism of Al–Zr-based materials, the Al2Zr alloy was oxidized in a wet atmosphere. Water vapor achieves the synchronous oxidation of Al and Zr to form amorphous (Al0.67Zr0.33)O1.66 oxide on the Al2Zr surface. The oxidation kinetics of the Al2Zr alloy is significantly retarded by the presence of water vapor. Compared with the oxygen molecules, water molecules are preferentially adsorbed on the surface, thereby providing fewer oxidizing species for wet oxidation than those for oxygen-involved oxidation. This work provides fundamental insights for surficial protection of structural alloys in humid environments. [ABSTRACT FROM AUTHOR]

The high-temperature oxidation of ZrAl2 upon exposure to pure O2 at 800–950 °C was studied in terms of the oxidation kinetics and the formation mechanism of the oxide layer. The alloy followed parabolic oxidation kinetics, and the activation energy of oxidation was 239 ± 14 kJ/mol. During the early stages of oxidation below 850 °C, a single-layer oxide formed due to the crystallization of the initially formed amorphous oxide layer. A multilayer oxide structure developed at higher temperatures, due to the slightly higher affinity of oxygen for Zr than for Al and the oxidation-induced compositional changes. [ABSTRACT FROM AUTHOR]

The high-temperature oxidation of ZrAl2 upon exposure to pure O2 at 800–950 °C was studied in terms of the oxidation kinetics and the formation mechanism of the oxide layer. The alloy followed parabolic oxidation kinetics, and the activation energy of oxidation was 239 ± 14 kJ/mol. During the early stages of oxidation below 850 °C, a single-layer oxide formed due to the crystallization of the initially formed amorphous oxide layer. A multilayer oxide structure developed at higher temperatures, due to the slightly higher affinity of oxygen for Zr than for Al and the oxidation-induced compositional changes. [ABSTRACT FROM AUTHOR]

Structural disordering leads to outstanding mechanical properties of amorphous alloys. Many properties are strongly related to formation of surface oxide layers. An in-depth understanding of effect of structural disordering of amorphous alloys on oxide evolution is essential for applications. This paper presents a review of recent comparative oxidation studies of Zr-based amorphous and single-phase crystalline counterpart alloys. Three representative model alloy systems are selected: Zr–Cu and Zr–Al representing alloys with components of different and similar oxygen affinities, respectively, and Zr–Cu–Al representing multi-component alloys. In combination with molecular dynamic simulations, the fundamental role of the structural disordering of parent alloys in the oxidation processes is revealed. The oxidation of Zr–Cu–Al–Ni amorphous alloys at the supercooled liquid temperature region is further reviewed to clarify the relationship between oxidation and substrate crystallization. • A focused review of role of structural disordering of amorphous alloys on thermal oxidation. • Three representative alloys with simple compositions were selected as model alloy systems. • Structural disorder of parent alloys influences strikingly oxide evolution and oxidation kinetics. • The disputes on the oxidation kinetics of amorphous and crystalline states were clarified. [ABSTRACT FROM AUTHOR]

• The commonly disregarded role of noble constituents on the oxidation of metallic glasses is revealed. • Amorphous Cu-Zr-Al alloys are designed as a model system which contains one noble and two similarly ignoble constituents. • The oxidation for Cu-poor Cu-Zr-Al alloy involves synchronous oxidation of Zr and Al. • Chemical interaction of Cu with Al in the Cu-rich Cu-Zr-Al alloys induces preferential oxidation of Zr over Al. • The study offers a new perspective for rational design of surficial oxide structures. The competition between synchronous oxidation and preferential oxidation of Zr and Al in amorphous Cu-Zr-Al alloys has been investigated. Oxide-layer growth on Cu-poor Cu-Zr-Al alloys occurs by synchronous oxidation of Zr and Al. However, for relatively high Cu alloying contents, synchronous oxidation of Zr and Al becomes disturbed by the increased chemical interaction of Cu with Al, which immobilizes Cu and Al atoms from oxidation. Consequently, only Zr is preferentially oxidized. The findings provide fundamental insights on the role of nobler alloy constituents on the oxidation mechanism of multi-component alloys, which opens new avenues for rational design of surficial oxide structures. [ABSTRACT FROM AUTHOR]

• The fundamental role of atomic structure on thermal oxidation of alloys is revealed. • Al-Zr was selected as the model alloy system to circumvent preferential oxidation effect. • Structural order of parent alloys influences strikingly oxide compositions and oxidation kinetics. • Underlying mechanisms were disclosed by molecular dynamics simulations. • The study offers a new perspective in the field of surface engineering. To reveal the fundamental role of structural order of the parent alloy on the oxidation mechanism, thermal oxidation of amorphous and crystalline Al–Zr alloys with identical compositions were investigated in detail. An (Al 0.68 Zr 0.32)O 1.66 amorphous oxide emerged on crystalline Al 2 Zr, whereas an (Al 0.33 Zr 0.67)O 1.83 amorphous oxide formed on amorphous Al 68at.% Zr 32at.% under the same conditions. Oxidation kinetics was fast and linear for crystalline Al 2 Zr but slow and parabolic for amorphous Al 68at.% Zr 32at.%. The underlying mechanisms of such striking differences were disclosed by molecular dynamics simulations. The findings thus offer new prospects in the field of surface engineering. [ABSTRACT FROM AUTHOR]

• Thermal oxidation of amorphous Cu-Zr alloys with different Cu/Zr ratios has been studied. • High-resolution AES depth profiling and cross-sectional analytic HRTEM analyses were performed. • Cu-enriched nanoparticles emerge due to localized Cu-accumulation by selective oxidation of Zr. • Microstructures of Cu-enriched nanoparticles depend on stabilities of parent alloys. • The composition-dependent microstructure of oxidized Cu x Zr 1− x influences oxidation kinetics. The thermal oxidation of amorphous Cu–Zr alloys with different Cu:Zr ratios was studied by X-ray diffraction, Auger electron spectroscopy, and cross-sectional transmission electron microscopy. It was revealed that amorphous ZrO 2 /Cu-enriched bilayers are formed on the amorphous Cu–Zr alloys at 200–250 °C by the selective oxidation of Zr atoms in the alloys. Amorphous Cu-enriched particles (diameter: ~10 nm) are distributed randomly in the amorphous Cu-enriched sublayer of the am-Cu 33at.% Zr 67at.% alloy, due to the sluggish atomic diffusion in the amorphous Cu-enriched layer. In contrast, crystalline Cu-enriched particles (diameter: ~20 nm) are distributed densely in the amorphous Cu-enriched sublayer of the Cu 50at.% Zr 50at.% alloy. The different states of the Cu-enriched particles in the amorphous Cu-enriched sublayer of the am-Cu 33at.% Zr 67at.% and Cu 50at.% Zr 50at.% alloys are ascribed to thermodynamic reasons. The oxidation rate of amorphous Cu 50at.% Zr 50at.% alloy is faster than that of amorphous Cu 33at.% Zr 67at.% alloy, since the crystalline nanoparticles in the Cu-enriched sublayer provide fast migration pathways for ions, whereas the thick amorphous Cu-enriched sublayer presents as a diffusion barrier in the case of amorphous Cu 33at.% Zr 67at.% alloy. [ABSTRACT FROM AUTHOR]