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Fatigue crack threshold and growth behaviour in a near fully-lamellar gamma based titanium aluminides

Wang, Shiyuan (2015)
Ph.D. thesis, University of Birmingham.

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Abstract

Fatigue crack threshold (\(D\)K\(_{th}\)) and fatigue crack growth of a near fully-lamellar \(y\)-TiAl alloy (Ti-4522XD alloy) have been investigated in air at room temperature, 400, 650, 700 and 750 oC and at three R ratios (0.1, 0.5 and 0.8). Studies were carried out on both corner-cracked specimens and smooth specimens. A combination of a \(D\)K- increasing loading method and growing a crack from notch were applied throughout the tests. As a consequence of consistent material microstructure, use of standardized testing procedure and a sufficient number of tests, some trends in fatigue threshold and crack growth have been established, including: trends include: lack of dependence of (\(D\)K\(_{th}\)) values on test temperature; average (\(D\)K\(_{th}\)) values decrease with increasing R ratio; a strong dependence of crack growth rate on K\(_{max}\) values at RT; a reduced dependence of crack growth rate on K\(_{max}\) values and increased plasticity at elevated temperatures; crack blunting causes a reduction of fatigue crack growth rate at R=0.8 and at elevated temperatures; and little effect of test temperature on ‘fracture toughness’ values. Above all, the origins of naturally initiated cracks under cyclic loading are often found to be centered on up to four colonies which have failed by interlamellar fracture.

Type of Work:Ph.D. thesis.
Supervisor(s):Bowen, Paul and Li, Hang Yue
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Metallurgy and Materials
Subjects:TN Mining engineering. Metallurgy
Institution:University of Birmingham
ID Code:6347
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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