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-10A1-5Ti (Zr53), Zr-30Cu-10Al-5Ni (Zr55), and Zr-15Cu-10Al-10Ni (Zr65), were studied over the temperature range of 300-500degreesC in dry air. Oxidation kinetics of these alloys generally followed a parabolic rate law at T > 350 degreesC, but linear kinetics was obeyed at 300-350 degreesC. 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 tetragonaland monoclinic-ZrO(2) (t- and m-ZrO(2)), and minor CuO and NiO (only detected in Zr53). The amount of m-ZrO(2) formed strongly depends upon the alloy composition, exposure time, and temperature. TEM results showed that a significant amount of nano-grained Zr(2)Cu polycrystals formed beneath the amorphous oxide-scale in Zr53, indicating phase transformation has taken place. By contrast, Zr55 and Zr65 amorphous substrates transformed into Zr(2)Cu and ZrAl after oxidation. (C) 2004 Elsevier Ltd. All rights reserved.