Materials Science and Engineering Location: Zoom
Add to Calendar 2021-06-16T13:00:00 2021-06-16T15:30:00 America/New_York Ph.D. Dissertation Defense: Rachel Guarriello Title:    Effects of Boria on Environmental Barrier Coating Systems Zoom

Title:    Effects of Boria on Environmental Barrier Coating Systems

Abstract:  SiC/BN/SiC ceramic matrix composites (CMCs) with rare earth silicate (Yb2Si2O7) environmental barrier coating (EBC) systems entered use in civilian turbine engines in 2016.  The BN fiber/coating interphase has been found to oxidize to form boria on the surface of the CMC.  Exposures of CMC/ EBC systems in combustion environments have shown possible spinodal decompositions and dendritic structure formation attributed to boria formation and reaction with the Yb2Si2O7. However, no thermodynamic data and few experimental studies exist on the B2O3-SiO2-Yb2O3 system to confirm these interactions.  Due to the lack of data on this system, this dissertation seeks to determine the effect of boria on the EBC system through the following objectives:

 

  1. Understand the reactions and equilibrium phases that occur when B2O3 reacts with the phases found in the rare earth silicate EBC; Yb2Si2O7, Yb2SiO5, and Yb2O3.

 

  1. Develop a phase diagram for the Yb2O3 – SiO2 – B2O3 ternary system.

 

  1. Determine the properties of any reaction products and equilibrium phases that are found to form in the Yb2O3 – SiO2 – B2O3 ternary system.

 

  1. Determine the impact of the formation of these reaction products on the oxidation of SiC/BN/SiC CMC -Si bond coat, and thermochemical stability of theYb2Si2O7 EBC systems

 

Committee:

Dr. Jon Ihlefeld (Chairperson) – UVA MSE

Dr. Chris Benmore (Argonne National Lab, Lemont. IL)

Dr. Andres Clarens, UVA ESE

Dr. Bi-Cheng Zhou – UVA MSE

Dr. Elizabeth Opila, Adviser, MSE

 

Zoom:  https://virginia.zoom.us/j/97992705073

Email Peggy Gibson for the Passcode

 

All interested persons are invited to attend