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Title: The corrosion behaviour of high velocity oxy-fuel NiAl intermetallic coatings
Author: Hearley, J. A.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1999
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This thesis is a contribution to research into the corrosion behaviour of high velocity oxy-fuel (HVOF) thermally sprayed NiAl coatings. Investigations initially concentrated on the spraying of intermetallic compounds (IMCs), in particular NiAl. Results showed that NiAl could be successfully deposited as an IMC onto a 2.25Cr-1Mo substrate to produce a high quality coating of low porosity and excellent adhesion. The feasibility of using lower cost, less corrosion resistant substrates with a high performance protective coating offers the possibility of enhanced cost effectiveness allied with increased serviceability and ongoing environmental benefits. HVOF gun spray parameters were also optimised for the coating and it was found that they have a strong influence on coating properties. The most important parameter is the oxygen-fuel ratio as it influences the temperature, stoichometry and power of the flame. Coatings were sprayed under different ratios of fuel and oxygen flow rates and evaluated in terms of porosity, oxide content, Young's modulus and hardness. It was discovered that an increase in the oxygen-fuel ratio gave a coating of lower porosity with a higher oxide content, Young's modulus and improved hardness. The coatings showed excellent resistance to isothermal and cyclic oxidation due to the formation of an adherent and continuous alumina (A12O3) scale. The corrosion behaviour in air-chlorine mixtures has also been evaluated at high temperatures along with resistance to thermal cycling. Initial results showed that the coating provided improved properties compared with some conventional materials. Preliminary hot corrosion testing with one real and three synthetic ashes revealed satisfactory coating performance. It was found that the coating microstructure was influential. In addition, results in erosion testing showed that good corrosion resistance is combined with excellent protection against this form of wear.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available