FIRST-PRINCIPLES CALCULATIONS AND THERMODYNAMIC MODELING OF THE HF-RE BINARY SYSTEM WITH EXTENSION TO THE HF-NI-RE TERNARY SYSTEM

Open Access
Author:
Ling, Yan
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 08, 2011
Committee Members:
  • Paul Raymond Howell, Thesis Advisor
  • Zi Kui Liu, Thesis Advisor
Keywords:
  • thermodynamics
  • Ni-Hf-Re
  • hafnium
  • rhenium
  • Hf-Re
  • CALPHAD
  • first-principles
  • Ni-based superalloys
  • modeling
Abstract:
This thesis describes the thermodynamic modeling of the Hf-Re binary system and prediction of the Ni-Hf-Re ternary system. Hafnium and rhenium are both alloying elements in the nickel-based superalloys which are extensively used in the aerospace industry due to high creep and oxidation resistance. Nickel-based superalloys typically contain many alloying materials in addition to Hf and Re; therefore, a comprehensive understanding of the complex phase equilibria of this multi-component system becomes necessary. However, an empirical approach is both time consuming and costly. A more efficient approach is the CALPHAD (CALculation of PHAse Diagrams) method where a complete thermodynamic database is predicted through the summation of the thermodynamic properties of individual phases. In the absence of experimental data, first-principles calculations can be used to predict thermochemical data. The Hf-Re binary system has three intermetallic compounds, two of which show solubility ranges. SQS (Special Quasirandom Structure) calculations are performed on the bcc and hcp solid solution phases to predict the enthalpies of mixing. SQS calculations are also performed on the Hf-Zr and Re-Zr binary systems, the latter of which strongly resembles the Hf-Re system. RDF (Radial Distribution Function) analysis is used to investigate symmetry preservation of the parent structures. The Ni-Hf-Re ternary system is predicted by combining the thermodynamic descriptions of the three constituent binary systems: Hf-Re, Hf-Ni, and Re-Ni. The latter two systems have been previously modeled. An experimental isothermal section at 1173 K is included.