Effect of structural order on oxidation kinetics and oxide phase evolution of Al–Zr alloys

On the competition between synchronous oxidation and preferential oxidation in Cu-Zr-Al metallic glasses

“…This indicates that oxide-layer growth at these relatively low temperatures occurs by synchronous oxidation of Zr and Al from the parent alloy, which complies with the much higher O affinities of Zr and Al as compared to Cu, as well as the deep minimum for the Gibbs energy of formation of the amorphous am-(AlO1.5)y(ZrO2)1-y phase of fixed composition y = 0.33 (corresponding to (Zr0.67Al0.33)O1.83), as predicted in the previous study of oxidation of amorphous Al-Zr alloys [25]. As shown in our previous work on the oxidation of crystalline and amorphous binary Al-Zr alloys [22], the formation of an amorphous (Zr,Al)-oxide layer (with the same Al/Zr-ratio J o u r n a l P r e -p r o o f as compared to the alloy) results from the continuous dissolution of O into the amorphous alloy matrix at the oxide growth front. Oxide nucleation is triggered if the solubility product zone for the formation of the am-(AlO1.5)y(ZrO2)1-y phase in the O-dissolution zone is exceeded.…”

“…The pre-deposited ultra-thin (thickness: 2-3 nm) inert Au markers remained on top of the oxide surface, instead of being buried within or below the thickening oxide overlayer. This suggests that oxide-layer growth occurred mainly at the interface between the developing oxide layer and the parent alloy (further designated as the oxide growth front) through inward diffusion of oxygen anions (with concurrent outward diffusion of anion vacancies, as generated at the oxide/alloy interface by continuous dissolution of oxygen into the parent alloy), in accordance with the oxidation mechanism for pure Zr metal [54,55] and Zr-Al alloys [22].…”

“…Several studies on the oxidation of amorphous Zr-Al [22][23][24][25][26][27], Cu-Zr [28][29][30][31][32][33] and even Cu-Al [34][35][36] binary alloys have been reported in the literature. Cu-Zr binary alloys have the greatest glass-forming ability [37] among these three alloy systems.…”

“…[43][44][45][46][47][48][49]. Based on the previous oxidation studies of Al2Zr binary alloys [22,25,50], it may be presumed that thermal oxidation of amorphous Cu-Zr-Al ternary alloys with a similar Al/Zr atomic ratio of ½ should also result in the formation of a stable amorphous (Zr0.67Al0.33)O1.83 passive layer by synchronous oxidation of Zr and Al (since Cu has a much lower oxygen affinity). To experimentally verify this hypothesis, the thermal oxidation of amorphous Cu-Zr-Al ternary alloys were investigated as function of the nominal composition, while superimposing the following two criteria: (i) the Al:Zr atomic ratio of the alloys is fixed at 0.5 J o u r n a l P r e -p r o o f with varying Cu content, and (ii) the alloys should possess a good GFA.…”

Oxidation of a Zr46Cu46Al7Gd1 bulk metallic glass detected via optical characterizations

“…Although the oxygen affinity of Gd is the highest among the constituent elements [10,17,18], the formation of Gd oxide may require long-range diffusion that prevents its formation at lower temperature. Therefore, Zr is easier to react with oxygen to form ZrO 2 layer over the surface by inward diffusion of oxygen [19][20][21].…”