Effect of composition and microstructure on the oxidation and corrosion performance of Ni-based superalloys

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dc.contributor.authorHeggadadevanapura Thammaiah, Mallikarjuna
dc.contributor.examiningcommitteeOjo, Olanrewaju (Mechanical Engineering) Oliver, Derek (Electrical and Computer Engineering) Chen, Daolun (Mechanical and Industrial Engineering, Ryerson University)en_US
dc.contributor.supervisorCaley, William F. (Mechanical Engineering) Richards, Norman L. (Mechanical Engineering)en_US
dc.date.accessioned2019-09-04T16:01:14Z
dc.date.available2019-09-04T16:01:14Z
dc.date.issued2019-02en_US
dc.date.submitted2019-09-03T17:04:25Zen
dc.degree.disciplineMechanical Engineeringen_US
dc.degree.levelDoctor of Philosophy (Ph.D.)en_US
dc.description.abstractThe cyclic oxidation behaviour of three Ni-based superalloys IN738LC, Rene 80 and N5 was performed at 900°C for 1000 cycles including 1 h holding at oxidation temperature and cooling to room temperature by ambient air. Oxidation kinetics were determined by mass change measurement in each cycle. The cyclic oxidation resistance of N5 was found to be better than that of IN738LC and Rene 80; also, scale spallation for N5 was minimal compared to the other two alloys. Although both IN738LC and Rene 80 showed scale spallation, the rate was more severe in Rene 80 due to the combined effects of high Ti and formation of volatile Mo-rich oxides. The spallation in N5 was due to the formation of Ta-Hf-oxy carbides, which generate a high shear strain at the matrix-oxide and oxy-carbide interface. To assess the effect of γ' intermetallic size on the oxidation resistance of IN738LC, coupons (four sizes γ'; monomodal distribution) were subjected to isothermal and cyclic oxidation between 750-950ºC for 150 h/cycles respectively. Parabolic oxidation was found in all cases; based on rate constants, samples with the largest starting γ' were the most oxidation-resistant. Activation energies calculated from precipitate free zone (PFZ) thickness measurements were higher for samples with larger γ' (324 kJ/mole vs 279 kJ/mole). Decreasing the γ' precipitate size increases the oxidation rate of IN738LC. Sub-surface γ' precipitate dissolution was found to be γ' precipitate-size dependent. The interdiffusion coefficient for Al across the PFZ was found to decrease with increasing γ' size. The influence of γ' size and composition on the corrosion behaviour of IN738LC was also investigated while maintaining a monomodal microstructure. Experimental results showed a negative influence on the corrosion resistance of IN738LC with an increasing rate of cooling, which is attributable to an increase in the volume fraction of γ', i.e., reduction in chromium-containing matrix phase expose to the environment. Corrosion current density was found to be higher for a specimen with smaller γ' precipitates compared to specimens with larger precipitates. These results serve to further support the concept that oxidation resistance is indeed dependant on γ' intermetallic size whereby smaller precipitates exhibit a higher oxidation rate.en_US
dc.description.noteOctober 2019en_US
dc.identifier.urihttp://hdl.handle.net/1993/34147
dc.language.isoengen_US
dc.rightsopen accessen_US
dc.subjectCyclic oxidation, Ni-based superalloys, Oxidation behaviour, Scale spallation, Modelling, Cooling rate, Inter-diffusion, Dissolution, Microstructure, Precipitatesen_US
dc.titleEffect of composition and microstructure on the oxidation and corrosion performance of Ni-based superalloysen_US
dc.typedoctoral thesisen_US
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