Oxidation resistance of the supercooled liquid in Cu ₅₀Zr ₅₀ and Cu ₄₆Zr ₄₆Al ₈ metallic glasses

The oxidation behavior of Cu ₅₀Zr ₅₀ and Cu ₄₆Zr ₄₆Al ₈ glasses during continuous heating up to 1073 K has been investigated, with special emphasis on the oxidation resistance in the supercooled liquid (SCL) state. For Cu ₅₀Zr ₅₀, the oxide layer mostly consists of monoclinic ZrO ₂ (m-ZrO ₂), while for Cu ₄₆Zr ₄₆Al ₈, the oxide layer consists of two different layers: an outer layer consisting of tetragonal ZrO ₂ (t-ZrO ₂) + Al ₂O ₃ + metallic Cu (oxidation product from the SCL state of the glass matrix) and inner layer comprised of m-ZrO ₂ + metallic Cu islands (oxidation product from the crystallized matrix). Cu-enriched regions consisting of Cu ₅₁Zr ₁₄ (in Cu ₅₀Zr ₅₀) or AlCu ₂Zr + Cu ₇₀Zr ₁₅Al ₁₅ + Cu ₅₁Zr ₁₄ (in Cu ₄₆Zr ₄₆Al ₈) are present below the oxide layer. The present study shows that the addition of Al (8 at.%) in Cu ₅₀Zr ₅₀ results in a significant deterioration of the oxidation resistance in the SCL state since the solutionizing of Al in t-ZrO2 leads to a higher oxygen ion vacancy concentration, thus providing a higher activity of oxygen ions.