Session: 02-03 Mechanical Behavior of Ceramic Matrix Composites and Protective Coatings

Paper Number: 154264

Elevated Temperature Fracture Properties of Yb2Si2O7-Based Environmental Barrier Coatings 

TThe room and elevated temperature fracture properties of NASAs second generation Yb₂Si₂O₇ environmental barrier coating (EBC) were measured as manufactured by air plasma spray (APS) and field assisted sintering technology (FAST).  Noteworthy are the low fracture toughness and the physical and chemical instability of the APS material even after several hours of heat treatment.  Heat treatments were determined to increase hardness, elastic modulus, strength, and fracture toughness.  Although slow crack growth tests were attempted, the material instability and increasing strength during test limited the results.  For APS material in the as-sprayed condition, the room temperature Young’s modulus and fracture toughness are 45 GPa and 0.92 MPam^3/2 .  With brief heat treatments (~4 hours) Young’s modulus and the fracture toughness increase to 82 GPa and 1.36 MPaÖm.  In contrast to APS material, FAST material exhibits similar properties both as-processed and after brief heat treatment, with Young’s modulus and fracture toughness of  150 GPa and 1.36 MPam^3/2.  The fracture toughnesses of the EBCs are nearly constant up to 1316^oC.  Strength of APS material increased with test time at elevated temperatures due to improving bonds between particles.  Hardness measurements indicate that heat treatment changes the APS EBC from the surface inward with time, implying a diffusion driven reaction.

Presenting Author: Jonathan Salem NASA GRC

Presenting Author Biography: Jonathan Salem is a Materials Research Engineer at NASA Glenn Research Center. He received M.S. and Ph.D. degrees in Materials Science and Mechanical Engineering from the University of Washington, Seattle. He is a fellow of ASTM International and The American Ceramic Society. His work experiences include fracture studies of titanium and steel alloys, project leader for the Toughened Ceramics Life Prediction Program, International Space Station window reliability and development of mechanical testing standards for ceramics. Prior to working at NASA, he worked in Quality Assurance at Powell Valve and Forest City Foundries.

Authors:

Jonathan Salem NASA GRC
Michael Presby NASA GRC
Jamesa Stokes NASA GRC
Leland Hoffman HX5
Craig Smith NASA GRC
Rebekah Webster NASA GRC