Effect of Zr-content on the oxidation and phase transformation of Zr-base amorphous alloys in air

The oxidation and phase transformation of three Zr-base amorphous alloys, Zr–20Cu–12Ni–10Al–5Ti (Zr53), Zr–30Cu–10Al–5Ni (Zr55), and Zr–15Cu–10Al–10Ni (Zr65), were studied over the temperature range of 300–500 °C in dry air. Oxidation kinetics of these alloys generally followed a parabolic rate law at T>350 °C, but linear kinetics was obeyed at 300–350 °C. It was found that Zr65 was the most oxidation-resistant alloy among the three alloys studied. Scales formed on the alloys during oxidation consisted of mainly tetragonal- and monoclinic-ZrO2 (t- and m-ZrO2), and minor CuO and NiO (only detected in Zr53). The amount of m-ZrO2 formed strongly depends upon the alloy composition, exposure time, and temperature. TEM results showed that a significant amount of nano-grained Zr2Cu polycrystals formed beneath the amorphous oxide-scale in Zr53, indicating phase transformation has taken place. By contrast, Zr55 and Zr65 amorphous substrates transformed into Zr2Cu and ZrAl after oxidation.