New approaches to modelling thermo-chemo-mechanical couplings in hot corrosion
Abstract
Alloys and coatings used in high temperature applications are subject to surface degradation by oxidation. However, in most practica,l applications the surface degradation is also influenced by the presence of deposits on the component surfaces. Including coatings,is commonly thought of as a method to prevent the ingression of deposits onto the alloy surfaces. However, observations indicates th,at metallic components can be exposed to sulphate deposits, even if they are covered by a thermal barrier coating (TBC). Concomitant, reactions between the coating and melt alter the coating microstructure and properties. Environmental barrier coatings (EBCs) desig,ned to protect SiC-based ceramic matrix composites (CMCs) are nominally dense and ideally thermally matched to the substrate but are, chemically attacked by the melt yielding a reaction layer with less favourable thermal expansion characteristics. Hence, coating du,rability involves the interplay of complex thermochemical and thermomechanical interactions. These problems can be broken into three, classes which are the failure of coatings such as (i) dense EBCs and (ii) columnar TBCs that let deposits like Na2SO4 ingress to th,e alloy substrate but there is also a class of problem where there is (iii) failure of protective oxide coatings that form from reac,tant products. Many of the detailed chemical kinetics while known qualitatively are not quantified and thus what is required are gen,eral modelling frameworks that are flexible enough to allow new quantitative information to be added as data from measurements becom,e available. Here we will develop a series of thermodynamically motivated models that couple mechanics and chemistry to flexibly mod,els these three classes of problems. These include: (i) a damage mechanics framework for formation of distributed cracks; (ii) a the,rmo-chemo model for melt penetration in the oxides, TBCs and EBCs and (iii) a poro-plastic model for chemo-mechanical hot melt penet,ration in dense coatings. This class of models will be mainly for the oxide films and the EBCs.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 05, 2022
- Source ID
- N000142212434
Entities
People
- Vikram S Deshpande
Organizations
- Office of Naval Research
- United States Navy
- University of Cambridge