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Title: Deformation and fracture of an ultra-large grain near alpha titanium alloy
Author: Wilson, R. J.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1998
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The premature failure of gas turbine disc components constructed from near alpha titanium alloys under low temperature dwell loading have been attributed to areas of aligned alpha platelets in the specified basketweave microstructure. Attempts at modelling crack initiation within these aligned microstructures has either overlooked the anisotropic nature of alpha titanium or has been restricted by the lack of information on the stress/strain response of individual grains in these engineering alloys. To rectify this situation, fatigue crack initiation and propagation response in a large grained aligned alpha microstructure was studied and supported by an evaluation of the crystallographic orientation adjacent to the crack path. Fatigue crack initiation is shown to be highly dependent on the crystallographic orientation of the colony in which it occurs. Extended fatigue lives occur where basal planes of the initiating colony lie parallel to the applied load. Conversely, basal inclinations of 45° produce short fatigue lives. Stage II fatigue cracks propagate preferentially through colonies with common basal planes. Colony/grain boundaries and alpha lath direction affect crack propagation kinetics. Life to failure is inversely dependent upon applied stress range in all geometries studied. This relationship applies irrespective of whether the alloy cyclically softens or hardens.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available