Reaction systems and phase development for investment casting ceramics

Taylor, Benjamin Luke (2015). Reaction systems and phase development for investment casting ceramics. University of Birmingham. Ph.D.

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Abstract

Aero engine turbine blades are commonly produced via investment casting methods utilising sacrificial ceramic cores during casting to provide internal features such as cooling channels. During the firing process the conversion of the main ingredient (amorphous silica) to β-cristobalite plays a significant role, as it directly affects the dimensional stability, shrinkage, and leachability of the core after casting. Dilatometry, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilised to evaluate common additives such as zirconium silicate and aluminosilicate. Zircon was found to act as a nucleation site with high temperature stability while aluminosilicate acts as a flux enhancing cristobalite formation rates. This understanding was utilised to mimic the performance of the formulation using both a novel engineered material and alternative naturally sourced silica.

An innovative method was also developed utilising confocal Raman spectroscopy (CRM) and polarised light microscopy (PLM) for analysis of ceramic systems studied with a hot stage up to 1500 °C. Polarised light microscopy was shown to be favourable for analysis of crystal growth mechanisms and low temperature (≈250 °C) α-β cristobalite phase transitions. Developments in Raman spectroscopic technique enabled the location and crystallinity of devitrified amorphous silica (cristobalite) to be observed via a quasi-real time method, providing insight to the source, direction and corresponding crystal growth rates.

The combination of analytical techniques has provided sufficient understanding to explain the role of key components in ceramic core formulations, which can be used to improve control and the predictability of the system during development and manufacture.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):