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Title: Creep and creep fracture of the near-alpha titanium alloy IMI834
Author: Hull, R. J.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1994
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High precision uniaxial constant stress tests were carried out for the near-alpha titanium alloy IMI834. Testing was completed at 823, 848, 873, 898 and 923 K, and at stresses chosen to give rupture lives in the range of about one day to six months at each temperature. Over the entire range of testing conditions, predominantly tertiary normal creep curves were recorded. During creep an alpha-case developed at air exposed surfaces, whose depth varied according to a parabolic rate law with an activation energy of 208 kJmol-1. For tests failing after about 1000 hours at 848, 873 and 898 K, and 100 hours at 923 K, failure occurred due to the propagation of circumferential surface cracks which developed in the alpha-case. In contrast, for all tests at 823 K, and for rupture lives of less than 100 hours at 923 K, and for tests lasting less than about 1000 hours at the remaining temperatures, failure occurred due to the link up of creep cavities formed predominantly at the alpha/transformed beta interfaces. A conventional power law analysis of the creep data proved capable of describing the stress and temperature variation of the minimum creep rates and rupture lives. However, this approach gave no information concerning the evolution of creep strain with time. Consequently, the theta-projection concept and the continuum damage mechanics (CDM) constitutive equations were also fitted to the experimental data. Isothermal and anisothermal forms of each model were developed. These proved capable of representing the stress and temperature variation of the experimental failure times, minimum creep rates and failure strains. However, whilst the theta-projection method described entire creep curves, the creep curves constructed using CDM contained almost no primary stage.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available