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

摘要

To enhance the resistance to oxidation and prolong the lifetime, oxidation protection coatings were applied onudMo–9Si–8B (in at.%) alloy substrates by Si–B co-pack cementation. Subsequently, the samples were conditionedudat 1450 °C for 8 h in air to develop an outer 10 μmthick aluminoborosilicate scale. A multilayered microstructureudofMoSi2,Mo5Si3, andMo5SiB2/MoB of about 80 μmthick was observed underneath the scale. During cyclic testingudbetween room temperature and 1300 °C the samples exhibited a very low mass change of only up toud+/−0.2 mg/cm2 within 500 h at high temperature. During oxidation the MoSi2 phase layer was partiallyudconsumed by silica and Mo5Si3 formation. No high material regression due to MoO3-evaporation took placeudduring testing. However, a lowmass loss during the first 100 h of testingwas observed, presumably due to stressudcracking caused by thermalmismatch of coating and substrate accompanied by subsequent healing. The stressesudwere reduced by the growth texture in the [001] direction of the Mo5Si3-phase. In comparison to the uncoatedudsubstrate material, the mass change was decreased by 99.8%. This points to a significantly prolonged lifetimeudand shows the huge potential of coated Mo–9Si–8B alloys for application at very high temperatures and underudthermal cycling loads.