| MoSi2 coating is the most widely used on the surface of molybdenum alloy as high-temperature antioxidant coating,however,it is difficult for a single MoSi2 coating to meet the service conditions of ultra-high temperature environment and high-speed airflow scouring environment with the development of aerospace field.In this paper,MoSi2-Al2O3 coating and MoSi2-Al2O3-xHfC（x=2.5,5,7.5 and 10）coatings were prepared on the surface of molybdenum alloys by slurry sintering method with Mo,Si,Hf C and Al2O3 powders as the main raw materials.The static oxidation behavior of MoSi2-Al2O3 and MoSi2-Al2O3-xHfC（x=2.5,5,7.5and 10）coatings at 1500°C and 1600°C were studied respectively,and the phase transformation and antioxidant mechanism of the two coatings during oxidation were revealed.And the effect of Hf C particles on the oxidation performance of MoSi2-Al2O3 coatings was analyzed in a comparative study.The conclusions obtained during the study are as follows:（1）The MoSi2-Al2O3 coating prepared using the slurry sintering method has a distinct layered structure,and the coatings are MoSi2-Al2O3composite layer,MoSi2 layer and Mo5Si3 layer from outside to inside;similarly,the MoSi2-Al2O3-xHfC（x=2.5,5,7.5 and 10）coatings have a similar layered structure,and the coatings are MoSi2-Al2O3 composite layer,MoSi2-Hf C composite layer,MoSi2 layer and Mo5Si3 layer from outside to inside,respectively.（2）The MoSi2-Al2O3 coatings showed good high temperature oxidation resistance at 1500℃and 1600℃,and oxidation weight gain at both temperature conditions for 0～0.5 h,which reached the maximum values of 1.67 mg/cm2 and 3.67 mg/cm2 at 0.5 h,respectively,the coating oxidation for oxidation weight loss from 0.5 to 7 h,which reached the maximum values of 11.67 mg/cm2 and 22.85 mg/cm2 at 7 h,respectively,in the first stage of oxidation,MoSi2reacted with O2 to form Si O2 oxide layer on the surface,so it showed oxidation weight gain in the first stage,while in the second stage of oxidation,MoSi2 and Mo5Si3reacted with O2to form Mo O3,which is volatile above 750℃,the oxidation weight loss of the coating was more than the oxidation weight gain,so it showed oxidation weight loss in the second stage.During the oxidation process,there was a Si O2-mullite composite oxide layer with low oxygen transmission rate was formed on the surface of MoSi2-Al2O3 coating,which effectively improved the high temperature oxidation resistance of the coating.（3）MoSi2-Al2O3-xHfC（x=2.5,5,7.5 and 10）exhibited different antioxidant properties in high temperature environments,where the antioxidant properties of the coatings firstly increased and then decreased with the increase of Hf C content,and the MoSi2-Al2O3-5Hf C coatings showed the best antioxidant properties when the addition of Hf C was 5%.MoSi2-Al2O3-xHfC（x=2.5,5,7.5 and 10）coatings exhibited different high temperature oxidation resistance at 1500°C and 1600°C.The maximum oxidation weight loss of the coatings after oxidation at 1500°C for 7 h was 5.56 mg/cm2,2.78 mg/cm2,8.45 mg/cm2 and 9.67 mg/cm2,respectively,while the maximum oxidation weight loss of the coatings after oxidation at 1600°C for 7 h was 12.43 mg/cm2,6.78 mg/cm2,17.67mg/cm2 and 19.45 mg/cm2,respectively,so it can be seen from the maximum oxidation weight loss after oxidation for 7 h that the high temperature oxidation resistance performance of the coating at 1500℃is better than that at 1600℃.（4）MoSi2-Al2O3-xHfC showed superior high temperature oxidation resistance compared to MoSi2-Al2O3 coating.has When the MoSi2-Al2O3coating oxidation for 1 h,bubbles formed on the Si O2-mullite composite oxide layer,which provided a channel for oxygen diffusion to the substrate,and accelerated the oxidation failure of the coating,however,composite oxide layer（contains Si O2,Hf O2,Hf Si O4 and mullite）formed on the surface of MoSi2-Al2O3-xHfC,and the distribution of Hf O2 and Hf Si O4particles in the Si O2 oxide layer strengthened the Si O2 layer like a"skeleton",consequently,the surface of MoSi2-Al2O3-xHfC was basically free of bubbles.The composite oxide layer（contains Si O2,Hf O2,Hf Si O4and mullite）formed on the surface of MoSi2-Al2O3-xHfC effectively inhibited the diffusion of oxygen into the substrate and improved the high-temperature oxidation resistance of the coating.There are 56 figures,10 tables and 113 references... |
PDF Full Text Request