The time behaviour of surface applied fluorine inducing the formation of an alumina scale on gamma-TiAl during oxidation at 900 °C in air
Recently the target temperature of components manufactured from gamma-TiAl alloys like turbine blades, turbocharger rotors or automotive valves has been increased to 900 °C. However, there is an insufficient oxidation resistance above 750 °C. One method used to improve the gamma-TiAl oxidation behav...
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Published in | Intermetallics Vol. 14; no. 10; pp. 1136 - 1142 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Elsevier Ltd
01.10.2006
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Subjects | |
Online Access | Get full text |
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Summary: | Recently the target temperature of components manufactured from gamma-TiAl alloys like turbine blades, turbocharger rotors or automotive valves has been increased to 900
°C. However, there is an insufficient oxidation resistance above 750
°C. One method used to improve the gamma-TiAl oxidation behaviour is the so-called fluorine microalloying effect. After application of fluorine to the TiAl surface by ion implantation or treatment with diluted HF and oxidation at 900
°C in air a dense alumina layer is formed. The aim of this work was firstly to study the short time development of the fluorine concentration during heating up to 400–1000
°C (1
h/air) in steps of 100
°C. Using ion beam analysis the depth profiles of F, Al, Ti and O were obtained simultaneously and non-destructive. A distinct loss of fluorine was found between 400
°C and 500
°C. At temperatures above 800
°C an alumina layer was formed with fluorine maximum located at the metal/oxide interface. Secondly the long time behaviour during oxidation of up to 500
h/900
°C/air was investigated showing a slow fluorine decrease. The alumina layer acts as a diffusion barrier for fluorine, whereas fluorine diffuses into the metal. The diffusion coefficient was calculated. The results fit into the theoretical model assuming a selective transport of gaseous aluminium fluorides at the metal/oxide interface. |
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ISSN: | 0966-9795 1879-0216 |
DOI: | 10.1016/j.intermet.2006.01.063 |