Ductility in high chromium super-ferritic alloys
| dc.contributor.advisor | Ball, Anthony | en_ZA |
| dc.contributor.author | Wolff, Ira M | en_ZA |
| dc.date.accessioned | 2016-10-19T13:35:56Z | |
| dc.date.available | 2016-10-19T13:35:56Z | |
| dc.date.issued | 1989 | en_ZA |
| dc.description | Includes reprints of author's related articles. | en_ZA |
| dc.description | Bibliography: pages 187-201. | en_ZA |
| dc.description.abstract | The competition between microfracture and plastic flow has been studied in relation to the thermomechanical processing parameters and minor element chemistry of wrought super-ferritic alloys based on a composition of Fe-40wt% Cr. These alloys have been developed for corrosion-resistant applications, specifically by micro-alloying with platinum group metals to induce cathodic modification, but their use has been hampered by inadequate toughness at ambient temperatures. Brittle cleavage of the alloys is a consequence of the high resistance to plastic flow required to accommodate local stresses, such as those found ahead of a loaded crack. Once initiated, a crack propagates in a brittle manner with minimal ductility. The impact toughness therefore relies on the ability of the alloys to withstand crack initiation. The frequency of the crack initiation events is related to the distribution of secondary phases within the matrix and at the grain boundaries. A direct means of improving the toughness and the ductility is accordingly via annealing cycles and minor alloying additions to control the precipitation of second phases. The ductility is enhanced by raising the mobile dislocation density, and this may be achieved by pre-straining recrystallised material, or increasing the number of dislocation sources in the otherwise source-poor material. The generation of mobile dislocations by prismatic punching at second phase particles in response to local or tessellated stresses was found to increase the ductility and the impact toughness of the alloy. The addition of nickel also increases the brittle fracture resistance by promoting stress accommodation at the crack tip, a result which can, in principle, be explained on the basis of enhanced dislocation dynamics. The tendency of the alloys to form a stable recovered substructure was identified as a critical parameter for both the mechanical and corrosion properties. The low-angle dislocation sub-arrays contribute to overall strain-hardening, but destabilise the passivity of the alloys in acid media. In practice, rationalisation of the microstructural parameters has enabled the practicable fabrication of tough, corrosion-resistant alloys, suitable for commercial development. | en_ZA |
| dc.identifier.apacitation | Wolff, I. M. (1989). <i>Ductility in high chromium super-ferritic alloys</i>. (Thesis). University of Cape Town ,Faculty of Engineering & the Built Environment ,Centre for Materials Engineering. Retrieved from http://hdl.handle.net/11427/22200 | en_ZA |
| dc.identifier.chicagocitation | Wolff, Ira M. <i>"Ductility in high chromium super-ferritic alloys."</i> Thesis., University of Cape Town ,Faculty of Engineering & the Built Environment ,Centre for Materials Engineering, 1989. http://hdl.handle.net/11427/22200 | en_ZA |
| dc.identifier.citation | Wolff, I. 1989. Ductility in high chromium super-ferritic alloys. University of Cape Town. | en_ZA |
| dc.identifier.ris | TY - Thesis / Dissertation AU - Wolff, Ira M AB - The competition between microfracture and plastic flow has been studied in relation to the thermomechanical processing parameters and minor element chemistry of wrought super-ferritic alloys based on a composition of Fe-40wt% Cr. These alloys have been developed for corrosion-resistant applications, specifically by micro-alloying with platinum group metals to induce cathodic modification, but their use has been hampered by inadequate toughness at ambient temperatures. Brittle cleavage of the alloys is a consequence of the high resistance to plastic flow required to accommodate local stresses, such as those found ahead of a loaded crack. Once initiated, a crack propagates in a brittle manner with minimal ductility. The impact toughness therefore relies on the ability of the alloys to withstand crack initiation. The frequency of the crack initiation events is related to the distribution of secondary phases within the matrix and at the grain boundaries. A direct means of improving the toughness and the ductility is accordingly via annealing cycles and minor alloying additions to control the precipitation of second phases. The ductility is enhanced by raising the mobile dislocation density, and this may be achieved by pre-straining recrystallised material, or increasing the number of dislocation sources in the otherwise source-poor material. The generation of mobile dislocations by prismatic punching at second phase particles in response to local or tessellated stresses was found to increase the ductility and the impact toughness of the alloy. The addition of nickel also increases the brittle fracture resistance by promoting stress accommodation at the crack tip, a result which can, in principle, be explained on the basis of enhanced dislocation dynamics. The tendency of the alloys to form a stable recovered substructure was identified as a critical parameter for both the mechanical and corrosion properties. The low-angle dislocation sub-arrays contribute to overall strain-hardening, but destabilise the passivity of the alloys in acid media. In practice, rationalisation of the microstructural parameters has enabled the practicable fabrication of tough, corrosion-resistant alloys, suitable for commercial development. DA - 1989 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 1989 T1 - Ductility in high chromium super-ferritic alloys TI - Ductility in high chromium super-ferritic alloys UR - http://hdl.handle.net/11427/22200 ER - | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11427/22200 | |
| dc.identifier.vancouvercitation | Wolff IM. Ductility in high chromium super-ferritic alloys. [Thesis]. University of Cape Town ,Faculty of Engineering & the Built Environment ,Centre for Materials Engineering, 1989 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/22200 | en_ZA |
| dc.language.iso | eng | en_ZA |
| dc.publisher.department | Centre for Materials Engineering | en_ZA |
| dc.publisher.faculty | Faculty of Engineering and the Built Environment | |
| dc.publisher.institution | University of Cape Town | |
| dc.subject.other | Ferritic steel - Ductility | en_ZA |
| dc.subject.other | Iron alloys - Ductility | en_ZA |
| dc.subject.other | Materials Engineering | en_ZA |
| dc.title | Ductility in high chromium super-ferritic alloys | en_ZA |
| dc.type | Doctoral Thesis | |
| dc.type.qualificationlevel | Doctoral | |
| dc.type.qualificationname | PhD | en_ZA |
| uct.type.filetype | Text | |
| uct.type.filetype | Image | |
| uct.type.publication | Research | en_ZA |
| uct.type.resource | Thesis | en_ZA |
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