Isothermal Oxidation of Ti3Al0.6Ga0.4C2 MAX Phase Solid Solution in Air at 1000 °C to 1300 °C

The atomically laminated Ti2AlC, Ti3AlC2 and Cr2AlC MAX phases, with A = Al, form adherent, passivating alpha-alumina, Al2O3, oxide scales when heated in air. The effect of solid solutions on the A layers in affecting the oxidation kinetics remains a subject of open research. Herein we synthesize a dense bulk polycrystalline Ti3Al1-xGaxC2 (x approximate to 0.4) solid-solution and investigate its isothermal oxidation in ambient air, in the 1000 degrees C-1300 degrees C temperature range, for times varying between 15 and 300 h. At 1000 degrees C, a passivating dense Al2O3 layer ( approximate to 1-2.6 mu m thick) with near cubic kinetics and an overall weight gain that is slightly less than either Ti3AlC2 or Ti2AlC is formed. At 1200 degrees C, the Al2O3 layer thickens (3.5-12 mu m thick) with some scale delamination on the corners initiating at 15 h. At 1300 degrees C, the Al2O3 layer (7.6-20.7 mu m thick) wrinkles and Al2TiO5 forms. Though the Al2O3 grains coarsen at 1200 degrees C and 1300 degrees C, the weight gain is higher than that for Ti3AlC2 or Ti2AlC. At around 7 at. %, this is one of the lowest, if not lowest, Al mole fraction in a Ti-based alloy/compound that forms an Al2O3 passivating layer. We further provide compelling microstructural evidence, in the form of a duplex oxide, that at 1000 degrees C, the outward Al flux, J(Al), and the inward O flux, J(O), are related such that 2 J(Al) = 3 J(O). A fraction of these fluxes combine, at the duplex oxide interface, to nucleate small grains

Automated summary

By investigating the isothermal oxidation of Ti3Al1-xGaxC2 solid solution, the oxidation process at different temperatures was studied, and a low aluminum molar fraction alloy that can form a protective Al2O3 layer was discovered.