Oxidation behavior of pack-cemented Si–B oxidation protection coatings for Mo–Si–B alloys at 1300°C

• Published in: Surface & coatings technology Vol. 266; pp. 57 - 63
• Main Authors: Lange, Annika, Heilmaier, Martin, Sossamann, Travis A., Perepezko, John H.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25.03.2015
• Subjects: Mo–9Si–8B; Oxidation protection coatings; Pack cementation; Oxidation protection coatings; Pack cementation; Mo–9Si–8B
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2015.02.015

To enhance the resistance to oxidation and prolong the lifetime, oxidation protection coatings were applied on Mo–9Si–8B (in at.%) alloy substrates by Si–B co-pack cementation. Subsequently, the samples were conditioned at 1450°C for 8h in air to develop an outer 10μm thick aluminoborosilicate scale. A multilayered microstructure of MoSi2, Mo5Si3, and Mo5SiB2/MoB of about 80μm thick was observed underneath the scale. During cyclic testing between room temperature and 1300°C the samples exhibited a very low mass change of only up to +/−0.2mg/cm2 within 500h at high temperature. During oxidation the MoSi2 phase layer was partially consumed by silica and Mo5Si3 formation. No high material regression due to MoO3-evaporation took place during testing. However, a low mass loss during the first 100h of testing was observed, presumably due to stress cracking caused by thermal mismatch of coating and substrate accompanied by subsequent healing. The stresses were reduced by the growth texture in the [001] direction of the Mo5Si3-phase. In comparison to the uncoated substrate material, the mass change was decreased by 99.8%. This points to a significantly prolonged lifetime and shows the huge potential of coated Mo–9Si–8B alloys for application at very high temperatures and under thermal cycling loads. •The improvement in mass change comparing coated and uncoated samples is remarkable.•The mass change was decreased by 99.8% comparing coated and uncoated materials.•This shows the potential of coated Mo–9Si–8B for application at high temperatures.•The interdiffusion growth of the multilayer structure shows a preferential behavior.