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Title: Fatigue crack threshold and growth behaviour in a near fully-lamellar gamma based titanium aluminides
Author: Wang, Shiyuan
ISNI:       0000 0004 5371 8649
Awarding Body: University of Birmingham
Current Institution: University of Birmingham
Date of Award: 2015
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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.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council (EPSRC) ; Rolls-Royce plc
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TN Mining engineering. Metallurgy