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Project submitted for MASTER OF MECHANICAL ENGINEERING RPI East Hartford, CT Presented by

Dependence of Fracture Toughness of Ceramic Thermal Barrier Coatings on Microstructure: Electron Beam Physical Vapor Deposition vs. Air Plasma Spray. Project submitted for MASTER OF MECHANICAL ENGINEERING RPI East Hartford, CT Presented by Danh Tran 8/10/2014. Outlines. Objectives

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Project submitted for MASTER OF MECHANICAL ENGINEERING RPI East Hartford, CT Presented by

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  1. Dependence of Fracture Toughness of Ceramic Thermal Barrier Coatings on Microstructure:Electron Beam Physical Vapor Deposition vs. Air Plasma Spray Project submitted for MASTER OF MECHANICAL ENGINEERING RPI East Hartford, CT Presented by Danh Tran 8/10/2014

  2. Outlines • Objectives • Thermal Barrier Coatings Processes - Air Plasma Spray (APS) - Electron Beam Physical Vapor Deposition (EB-PVD) • Fracture Toughness Measurement using Vickers Nano-indentation method • Microstructure of samples - APS - EB-PVD • Results - Compare Fracture Toughness (KIC) of APS vs. EB-PVD

  3. Objectives • To Compare Fracture Toughness of ceramic layer deposited by different Thermal Barrier Coatings processes: • Air Plasma Spray (APS) vs. Electron Beam – Physical Vapor Deposition • To Observe crack characteristics of ceramic layer by both processes

  4. x Ceramic Bond Coat Substrate Active Introduction TBCs reduces metal temperature of gas turbine blades

  5. TBCs processes - Air Plasma Spray (APS) APS provides multi-layer ceramic with splat structure

  6. TBCs processes – Electron Beam Physical Vapor Deposition (EB-PVD) EB-PVD provides ceramic with columnar structure ± 30° • A simple EB-PVD process: • Under vacuum (10-4 to 10-5 torr) • Bending of the electron beam is obtained by a magnetic field perpendicular to the drawing.

  7. Vickers Test Diagram c Fracture Toughness (KIC) The fracture toughness KIC, is a measure of the material’s resistance to the propagation of a crack. where: KIC : Fracture Toughness (MPa-m1/2) K : empirical constant (no unit) E : Young’s Modulus (GPa) HV : Vickers Hardness (GPa) P : Load (N) c : crack length (m) K = 0.036 (Ref.)

  8. TBCs Microstructures • APS process provides multi-layer ceramic with splat structure • EB-PVD provides columnar structure EB-PVD Columnar microstructure APS microstructure

  9. Crack length & Fracture Toughness Experiment • Prepare two Thermal Barrier Coatings samples • One from APS process • One from EB-PVD process • Apply loads on samples at multiple locations (using Vickers Hardness Tester): – 25gf , 50gf, 100gf and 200gf (*) (*) NOTE: Applied load based on tester’s minimum load as starting point • Record Hardness data from applied loads • Measure & compare crack lengths under microscope between two processes

  10. c Vickers Test Diagram Crack length & Fracture Toughness Experiment (cont’) Ceramic from APS, cracks widely spread to surrounding area Measured crack’s length on APS samples: Load = 25gf Mag = 500X

  11. c Vickers Test Diagram Crack length & Fracture Toughness Experiment (cont’) Ceramic from EB-PVD, cracks propagate within grain boundary Measured crack’s length on APS samples: Load = 25gf Mag = 500X

  12. Results Average crack from APS is longer than EB-PVD at each applied load Reason: APS has lower fracture toughness

  13. Results (cont’) Average Vickers Hardness from APS is lower than EB-PVD’s

  14. Slope 314 Slope 111 Results (cont’) • Smaller slope requires bigger load to increase crack length • Ceramic from EB-PVD process is harder than APS’s

  15. Conclusions • For each applied load: - Vickers hardness of ceramic from APS is lower than EB-PVD - Average crack from APS is longer than EB-PVD’s • Ceramic from APS has lower KIC than EB-PVD’s • Empirical constant, K, which was determined from literature, is applicable for this experiment • Ceramic from APS process is more brittle compare to EB-PVD’s under constant loading condition

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