Oxidation Limited Lifetime of Ni‐Base Metal Foams in the Temperature Range 700–900 °C

Abstract INCONEL 625 metal foams produced from alloy powder by the slip‐reaction‐foam‐sinter‐process are tested in respect to cyclic oxidation behavior in air in the temperature range 700–900 °C. The structure of the oxide scales formed on the foam particles is characterized using optical microscopy and SEM/EDX analysis. Main emphasis is put on studying the oxidation limited lifetimes of the foams as function of temperature and foam microstructure. It is shown that mechanical disintegration during long term oxidation at the highest test temperatures is caused by a critical depletion of the Cr content in the alloy as a result of the growth of the initially formed surface chromia layer. This results in chemical breakaway due to accelerated oxide growth of voluminous Ni‐rich oxide on chromium exhausted alloy particles. Lifetime modeling based on calculation of Cr‐depletion in the alloy at the oxide/metal interface of each individual foam particle using the DICTRA software is in good agreement with the experimentally determined values of the time to breakaway.