The article addresses effects of silicate deposit composition on reactions with yttrium monosilicate (YMS), a candidate environmental barrier coating for aero-engine components. Computed phase equilibria are used to predict the nature and relative proportions of reaction products and the extent of YMS consumption upon reaction with twelve deposits of varying composition at 1300°C. These predictions are compared with results of a corresponding experimental study on three exemplary deposits. Although the nature and sequence of reaction products formed (typically apatite and yttrium disilicate) depend on the Ca:Si ratio of the deposit, the degree of consumption of YMS at equilibrium is relatively insensitive to deposit composition and is predicted to proceed to a greater extent than that in yttrium disilicate. However, sluggish reaction kinetics associated with the formation of a thin apatite layer above the YMS prevents reactions from reaching their terminal equilibrium states within the experimental times investigated (250 hours). For deposit loadings of 18 mg/cm2 (corresponding to a thickness of about 100 µm), the degree of consumption following 250 hours exposures is only about 10%-40% of the predicted terminal values, depending on deposit composition.
Bibliographical noteFunding Information:
Research supported by Pratt & Whitney Center of Excellence in Composites at the University of California Santa Barbara. DLP gratefully acknowledges support through ONR grants N00014‐16‐1‐2702 and N00014‐17‐C‐2034, monitored by Dr D. Shifler. YMS pellets were kindly provided by GE Aviation. The research made use of the MRL Shared Experimental Facilities, a member of the NSF‐funded Materials Research Facilities Network ( www.mrfn.org ) supported by the MRSEC Program of the NSF under Award No. DMR 1121053. The authors thank Gareth Seward for assistance with EPMA and Weiwei Zhang for assistance with Thermo‐Calc.
- Environmental barrier coating
- chemical reactions
- yttrium silicate