COSIM is a computer program that numerically simulates oxidation and diffusion in a metallic coating layer on substrates made of nickel-base alloys. COSIM is primarily useful for analyzing the gradual deterioration and predicting the lifetimes of the protective coating on turbine blades and vanes. At typical high operating temperatures, such deterioration involves oxidation and interdiffusion characterized by times of the order of tens to thousands of hours.
COSIM implements a finite-difference mathematical model to simulate (1) the diffusion of chemical species within the coating including the solute needed to support the growth of a protective oxide scale, (2) diffusion between the coating and the substrate, and (3) oxidation. The program predicts concentration profiles for up to three elements in the coating and substrate after various oxidation exposures. Ternary cross terms and concentration-dependent diffusion coefficients are taken into account. Recession of the surface because of loss of solute is also predicted.
The program incorporates a previously developed mathematical model of growth and spalling of oxide, for use in simulation of either isothermal or cyclic oxidation exposures. The oxide-spalling submodel accounts for consumption of solute at higher rates in cases of cyclic oxidation accompanied by total or partial loss of the oxide scale. The program can predict the life of the coating layer(s) on the basis of a concentration-dependent or other failure criterion (e.g., the concentration of the solute at the surface falls to 2 percent). Hence, the program facilitates parametric studies for evaluation of tradeoffs among coating and substrate parameters (e.g., coating thickness, solute concentration) to obtain the same coating life or for identifying parameters that exert the greatest effect on coating life.
Written in an extension of FORTRAN 77, COSIM contains numerous subroutines that render it easily modifiable for application to different coating-oxidation problems.
This program was written by James A. Nesbitt of Glenn Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Software category.
Inquiries concerning rights for the commercial use of this invention should be addressed to
NASA Glenn Research Center
Commercial Technology Office
Attn: Steve Fedor
Mail Stop 4—8
21000 Brookpark Road
Refer to LEW-16754.