Abstract
The solidification of gamma TiAl alloys is of interest to the aerospace and automotive industries. A gamma TiAl multicomponent alloy: Ti-45.5Al-4.7Nb-0.2C-0.2B (at. %) has been the focus of a study to investigate the solidification conditions that led to a Columnar to Equiaxed Transition (CET) in a directional solidification experiment where traditional Bridgman solidification was combined in series with the power down method. In this paper, a numerical modelling result (a locus plot of columnar growth rate and temperature gradient) from this experiment is superimposed onto CET maps generated using an established analytical model for CET from the literature. A parametric study is carried out over suitable ranges of nucleation undercooling and nuclei density values. The predicted CET positions are compared with the experimentally measured CET position. Reasonable agreement is found at low levels of nuclei density. The paper concludes with estimates for the solidification conditions (nuclei density and nucleation undercooling) that led to the CET.
Highlights
Gamma titanium aluminide (γ–TiAl or TiAl) alloys are of interest to the aerospace and automotive industries on account of their low density and good mechanical properties at high temperature [1][2]
A gamma TiAl multicomponent alloy: Ti–45.5Al–4.7Nb–0.2C–0.2B has been the focus of a study to investigate the solidification conditions that led to a Columnar to Equiaxed Transition (CET) in a directional solidification experiment where traditional Bridgman solidification was combined in series with the power down method
The alloy: Ti–45.5Al–4.7Nb–0.2C–0.2B—referred to hereafter as alloy 455—is part of this study to investigate Columnar to Equiaxed Transition (CET) in transient directional solidification experiments carried out in a Bridgman furnace where traditional Bridgman solidification was combined with the power down method [6]
Summary
Gamma titanium aluminide (γ–TiAl or TiAl) alloys are of interest to the aerospace and automotive industries on account of their low density and good mechanical properties at high temperature [1][2]. Applications for TiAl alloys include (in aircraft engines): low pressure turbine (LPT) blades, stator vanes, and radial diffusers; and (in motorcar engines): turbocharger rotors and valve trains [3]. A 2nd generation TiAl alloy is in service in the LPT of General Electric’s ‘GEnx’ aeroengine which is used to power Boeing’s 787 Dreamliner aircraft [4]. %)—referred to hereafter as alloy 455—is part of this study to investigate Columnar to Equiaxed Transition (CET) in transient directional solidification experiments carried out in a Bridgman furnace where traditional Bridgman solidification was combined with the power down method [6]. CET is an unwanted phenomenon in cast components since two distinct microstructures may lead to discontinuous mechanical properties
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