Influence of W Content on the Oxidation Behaviour of Ternary $$\gamma ^{\prime }$$-Strengthened Co-Based Model Alloys Between 800 and $$900\,^{\circ }{\hbox {C}}$$

Abstract

The oxidation behaviour of ternary Co–Al–W alloys with W contents between 7 and 10 at. $$\%$$ was investigated in detail. Continuous thermogravimetry was conducted between 800 and $$900\,^{\circ }{\hbox {C}}$$ to compare the impact of $$\gamma ^{\prime }$$ volume fraction on the overall mass gain during the comparably long transient stages of oxide-scale growth. Resulting cross-sections were assessed using electron microscope-based analysis methods. To understand prevailing oxidation mechanisms, the development and composition of multilayered oxide scales were the main focus of the present study. Elemental distribution of three individual scale sections was investigated with electron probe microanalysis. No striking impact of the W level in the alloy was found. However, the development of diffusion-limiting barrier layers was demonstrated to change with varying W contents. Continuous alumina layers were only observed after 100-h exposure at $$800\,^{\circ }{\hbox {C}}$$ . For samples with 9 at. $$\%$$ W, the grain structure within the outer Co-oxide layer was characterized with electron backscattered diffraction after the maximum duration of exposure. Individual growth kinetics for three distinguished layers within the oxide scales were used to compare elemental transport depending on the W content in the alloy and the exposure temperature.