The purpose of this research work was to develop a nozzle capable of depositing dense CoNiCrAlY coatings via cold gas dynamic spray (CGDS) as well as compare the oxidation performance of bond coats manufactured by CGDS, high-velocity... more
The purpose of this research work was to develop a nozzle capable of depositing dense CoNiCrAlY coatings via cold gas dynamic spray (CGDS) as well as compare the oxidation performance of bond coats manufactured by CGDS, high-velocity oxy-fuel (HVOF) and air plasma spray (APS) at temperatures of 1000°C and 1100°C. The work was divided in two sections, the design and manufacturing of a CGDS nozzle with an optimal profile for the deposition of CoNiCrAlY powders and the comparison of the oxidation performance of CoNiCrAlY bond coats. Throughout this work, it was shown that the quality of coatings deposited via CGDS can be increased by the use of a nozzle of optimal profile and that early formation of protective α-Al2O3 due to an oxidation temperature of 1100°C as opposed to 1000°C is beneficial to the overall oxidation performance of CoNiCrAlY coatings.
A set of Ni-based single crystal superalloy aero-blade sections with electron beam physical vapour deposited thermal barrier coating (EBPVD-TBC) were used to investigate the role of substrate curvature on the microstructure and the... more
A set of Ni-based single crystal superalloy aero-blade sections with electron beam physical vapour deposited thermal barrier coating (EBPVD-TBC) were used to investigate the role of substrate curvature on the microstructure and the residual stresses in the coating system. The residual stresses generated in the thermal barrier coating (TBC) and the thermally grown oxide (TGO) have been evaluated non-destructively by Raman spectroscopy (RS) and photo-stimulated luminescence piezo-spectroscopy (PLPS), respectively. In addition, residual stresses were measured in free-standing individual columns extracted from the TBCs for further understanding of the large Raman shift towards the tension side in the ceramic layer. For the TGO, three areas with varied substrate curvature were mapped by PLPS. These residual stresses are analysed as a function of the thermal exposure and the substrate curvature. Discussion focuses on the implications on how to correctly evaluate the residual stresses in EBPVD-TBCs based on Raman shifts and subsequently the role of substrate curvature on the degradation of the microstructure and evolution of residual stresses in this type of TBCs.
ABSTRACT A multi-scale Finite Element Microstructure MEshfree (FEMME) fracture model for quasi-brittle materials with complex microstructures is applied to simulate thermo-mechanical damage in a plasma-sprayed thermal barrier coating... more
ABSTRACT A multi-scale Finite Element Microstructure MEshfree (FEMME) fracture model for quasi-brittle materials with complex microstructures is applied to simulate thermo-mechanical damage in a plasma-sprayed thermal barrier coating system. This novel multi-scale technique for damage simulation allows the influence of the microstruc-ture of the yttria-stabilized zirconia top coat and the geometry of the bond coat and the thermally grown oxide layer to be considered with computational efficiency. Mechanical damage, due to the thermal strain of an applied temperature difference, is predicted to decrease the top coat Young's modulus. The interaction between the evolution of damage and temperatures within the top coat is also simulated, demonstrating the capability of this methodology to address coupled multi-scale problems.
A multi-scale Finite Element Microstructure MEshfree fracture model (FEMME) for quasi-brittle materials with complex microstructures is applied to simulate thermo-mechanical damage in a plasma-sprayed thermal barrier coating system. This... more
A multi-scale Finite Element Microstructure MEshfree fracture model (FEMME) for quasi-brittle materials with complex microstructures is applied to simulate thermo-mechanical damage in a plasma-sprayed thermal barrier coating system. This novel multi-scale technique for damage simulation allows the influence of the microstructure of the yttria-stabilized zirconia top coat and the geometry of the bond coat and the thermally grown oxide layer to be considered with computational efficiency. Mechanical damage, due to the thermal strain of an applied temperature difference, is predicted to decrease the top coat Young’s modulus. The interaction between the evolution of damage and temperatures within the top coat is also simulated, demonstrating the capability of this methodology to address coupled multi-scale problems.
