• Green, Nicholas
• Cross, M.
• Shevchenko, Dmytro
• Croft, T. N.
• Mcbride, D.

Abstract

Components which best utilise the properties of high temperature titanium alloys are characterised by thin sections of a few millimetres thickness and hundreds of millimetres length. These alloys however are difficult to work with, being highly reactive in a molten state, necessitating a low superheat during processing. Centrifugal casting is therefore utilised as a production method, as under the centrifugal force, metal can fill thicknesses substantially less than a millimetre. However, due to the high liquid metal velocity developed there is a high risk of turbulent flow and of the trapping of any gas present within the liquid metal.<br/>This challenging application involves a combination of complex rotating geometries, significant centrifugal forces and high velocity transient free surface flows, coupled with heat transfer and solidification. Capturing these interacting physical phenomena, free surface flows, trapped air and associated defects is a complex modelling task. The authors have previously described the efforts needed to capture the bulk flow and liquid/solid coupling. This contribution will describe development and enhancements required to enable conventional free surface algorithms to capture the details of the flow: by maintaining a sharp metal-gas interface and reducing numerical diffusion whilst maintaining solution stability, on what are inevitably complex three dimensional geometries. Validation of the model has been done using a series of water experiments to capture the flow dynamics. Key observations arising from the work, such as capturing the dynamics of the pour conditions, were incorporated within the computational model.<br/>Modelling the casting, flow-thermal-solidification, of a TiAl alloy adds another layer of complexity. A bench-mark test case is employed to validate the effect of solidification on the fluidity of an aluminium alloy.<br/>

Topics

• impedance spectroscopy
• surface
• experiment
• aluminium
• reactive
• laser emission spectroscopy
• aluminium alloy
• defect
• titanium
• titanium alloy
• solidification
• centrifugal casting