Isothermal Oxidation Behaviour of a Two-Phase γ/γ′ Precipitation-Hardened Quaternary Pt-Based Alloys in Air at 1,350 °C

Abstract

High temperature oxidation behaviour of water-quenched and air-cooled Pt84:Al11:Cr3:Ru2 (at.%) alloy specimens in air at 1,350 °C, for up to 100 h exposure, was studied, and found to have properties similar to a Pt–10Al–4Cr alloy, but with no zone of discontinuous oxides. The mass gain of the alloy specimens as a function of time was monitored during isothermal exposure. The oxidized specimens were examined using a focused ion beam workstation with scanning electron microscopy, scanning electron microscopy with energy dispersive spectroscopy, optical microscopy, X-ray diffraction and Raman spectroscopy. The SEM images of specimen cross sections were used to determine the thicknesses of the Al2O3 scales for the various oxidation times. Well-adhering, continuous and protective α-Al2O3 scales with no spallation formed during oxidation, irrespective of the exposure time. There was neither a zone of discontinuous oxides, nor any other internal oxidation observed. The depth of the Al depletion zone was not detected. The oxide grain sizes increased with increased exposure time, and the scale growth kinetics obeyed the parabolic rate law. After 100 h exposure, scale of about 11.79 ± 1.39 μm thick had grown on the water-quenched specimen, while the scale thickness of the air-cooled specimen was about 13.84 ± 2.15 μm. The results suggest that the investigated alloy has a promising potential for high-temperature applications.