Design of 7 wt. percent Y_2O_3-ZrO_2/mullite plasma-sprayed composite coatings for increased creep resistance

摘要

Plasma-sprayed stand-alone coatings of 7 wt. percent Y_2O_3-ZrO_2 (YSZ), nominally 74 wt. percent Al_2O_3-26 wt. percent SiO_2 mullite, and a 46:54 volume ratio composite of YSZ to mullite were examined using X-ray diffraction, dilatometry, and compression creep. X-ray diffraction and dilatometer results showed that the as-sprayed predominantly amorphous mullite crystallized at 970 deg C. Creep tests were conducted on all three coating types in the as-sprayed condition at stresses from 40 to 80MPa and temperatures of 1000-1200 deg C. The primary deformation mechanism in coatings made from all three materials was stress-assisted densification of the porous coating. While the creep behavior of YSZ/mullite composite specimens was between that of pure YSZ and pure mullite specimens for all combinations of temperature and stress tested, the creep response of the composite was more similar to that of pure mullite for all cases tested, consistent with mullite being the continuous phase in the composite.