A combined approach for analysis of single crystal nickel base superalloys.

摘要

The purpose of this research is to develop a new tool for mechanical design and analysis of single crystal (SC) nickel base superalloys used in gas turbine engine components. The principle of this tool is based on the extension of the predictive models for isotropic material behavior to anisotropic materials such as SC nickel, base superalloys. This objective is achieved by combining the two main approaches used in the literature for SC materials development: the macroscopic approach and the microscopic approach. For that reason, this theory is designated as the "combined approach " (CA).;The structure of the CA theory requires two main elements: a viscoplastic model (that admits a yield function) and a slip factor. The viscoplastic model describes the behavior of the material in the macroscopic level. Conversely, the slip factor based on the crystallographic theory, accounts for the micro-slip state that dominates SC materials during deformation.;In order to determine the slip factor, a preliminary slip trace study of the crystal is established. Also to determine material constants from experimental data, a procedure has been developed to reduce the 3D basic equations into a one-dimensional form. The model has been evaluated for its predictive capability on SC material behavior including orientation dependence of the initial yielding, tension/compression asymmetry, stress-strain response, fully reversed cyclic response, creep response and relaxation response. In almost all the cases, good correlation has been observed between the predicted responses and experimental data, when available. Furthermore, it is believable that the CA can be successfully used for many other SC materials such as the body-centered-cubic (b.c.c) or the hexagonal-closed-packet (h.c.p). In view of all these results, the CA theory seems to offer the greatest promise in this regard. Limitations and future development needs are discussed.