Surface modification of titanium-based alloys

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dc.contributor.advisorKnutsen, Robert Den_ZA
dc.contributor.authorCamagu, Sigqibo Templetonen_ZA
dc.date.accessioned2014-07-31T10:21:54Z
dc.date.available2014-07-31T10:21:54Z
dc.date.issued2007en_ZA
dc.descriptionIncludes bibliographical references (leaves 97-101)
dc.description.abstractTwo routes of Oxygen Diffusion Hardening (ODH) have been investigated on two alloys of titanium, Ti-6AI-4V and Ti-6AI-7Nb (by weight). The first route involves a controlled atmosphere where argon saturated with water was used to transport water into the test pieces at elevated temperatures. The controlled atmosphere would encourage the generation of mono-atomic oxygen through the dissociation of water vapour, and therefore change the kinetics of physical absorption and diffusion of oxygen into titanium. The second route of ODH investigated was the Oxygen Boost Diffusion Hardening (OBDH). The oxygen boost diffusion hardening process was carried out in two steps. The first step was oxidation of the samples in air at elevated temperatures and the second step was to further diffusion treat the pre-oxidised test pieces III a vacuum or argon. Various temperature and time combinations were used on both steps of OBDH.The results revealed that the ODH heat-treatment in a controlled saturated argon environment was unsuccessful in developing a significant oxygen diffusion hardened layer. The OBDH process can be carried out to modify the surface properties of titanium and alloys. Both steps of this process play a vital role in achieving a thick modified layer for improved tribological properties of titanium and alloys. Performing the oxidation step of OBDH heat-treatment at higher temperatures results in higher surface hardness and deeper diffusion zone than carrying the oxidation step at lower temperatures for longer times provided there is no peeling of the oxide scale during the high temperature oxidation. The Ti-6AI-4V achieves higher surface hardness than the Ti-6AI-7Nb upon the same OBDH heat-treatment. The second step of the OBDH can also be carried out in an argon environment instead of vacuum. Carrying out the second step in an argon atmosphere allowed for higher surface hardness and thicker hardened zone than carrying the same step in vacuum. The effect of the OBDH on the underlying microstructures of two alloys under investigation is the depletion of the ɑ phase on the modified surface as a result of the diffused oxygen which stabilises the ɑ phase. Although higher surface hardness was achieved for the Ti-6AI-4V alloy than the Ti-6AI-7Nb alloy after the same heat treatment, the Ti-6AI-7Nb alloy achieved higher wear resistance due to more adherence of the oxide scale after the oxidation step. Despite achieving higher surface hardness and thicker hardened zone upon carrying out the second step of OBDH in an argon atmosphere than in vacuum, samples which underwent the second step of OBDH heat-treatment in vacuum exhibited higher wear resistance. Performing a twin cycle OBDH heat-treatment results in even higher surface hardness and higher wear resistance despite the severe scaling of the alloys upon the heat treatments.en_ZA
dc.identifier.apacitationCamagu, S. T. (2007). <i>Surface modification of titanium-based alloys</i>. (Thesis). University of Cape Town ,Faculty of Engineering & the Built Environment ,Centre for Materials Engineering. Retrieved from http://hdl.handle.net/11427/4967en_ZA
dc.identifier.chicagocitationCamagu, Sigqibo Templeton. <i>"Surface modification of titanium-based alloys."</i> Thesis., University of Cape Town ,Faculty of Engineering & the Built Environment ,Centre for Materials Engineering, 2007. http://hdl.handle.net/11427/4967en_ZA
dc.identifier.citationCamagu, S. 2007. Surface modification of titanium-based alloys. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Camagu, Sigqibo Templeton AB - Two routes of Oxygen Diffusion Hardening (ODH) have been investigated on two alloys of titanium, Ti-6AI-4V and Ti-6AI-7Nb (by weight). The first route involves a controlled atmosphere where argon saturated with water was used to transport water into the test pieces at elevated temperatures. The controlled atmosphere would encourage the generation of mono-atomic oxygen through the dissociation of water vapour, and therefore change the kinetics of physical absorption and diffusion of oxygen into titanium. The second route of ODH investigated was the Oxygen Boost Diffusion Hardening (OBDH). The oxygen boost diffusion hardening process was carried out in two steps. The first step was oxidation of the samples in air at elevated temperatures and the second step was to further diffusion treat the pre-oxidised test pieces III a vacuum or argon. Various temperature and time combinations were used on both steps of OBDH.The results revealed that the ODH heat-treatment in a controlled saturated argon environment was unsuccessful in developing a significant oxygen diffusion hardened layer. The OBDH process can be carried out to modify the surface properties of titanium and alloys. Both steps of this process play a vital role in achieving a thick modified layer for improved tribological properties of titanium and alloys. Performing the oxidation step of OBDH heat-treatment at higher temperatures results in higher surface hardness and deeper diffusion zone than carrying the oxidation step at lower temperatures for longer times provided there is no peeling of the oxide scale during the high temperature oxidation. The Ti-6AI-4V achieves higher surface hardness than the Ti-6AI-7Nb upon the same OBDH heat-treatment. The second step of the OBDH can also be carried out in an argon environment instead of vacuum. Carrying out the second step in an argon atmosphere allowed for higher surface hardness and thicker hardened zone than carrying the same step in vacuum. The effect of the OBDH on the underlying microstructures of two alloys under investigation is the depletion of the ɑ phase on the modified surface as a result of the diffused oxygen which stabilises the ɑ phase. Although higher surface hardness was achieved for the Ti-6AI-4V alloy than the Ti-6AI-7Nb alloy after the same heat treatment, the Ti-6AI-7Nb alloy achieved higher wear resistance due to more adherence of the oxide scale after the oxidation step. Despite achieving higher surface hardness and thicker hardened zone upon carrying out the second step of OBDH in an argon atmosphere than in vacuum, samples which underwent the second step of OBDH heat-treatment in vacuum exhibited higher wear resistance. Performing a twin cycle OBDH heat-treatment results in even higher surface hardness and higher wear resistance despite the severe scaling of the alloys upon the heat treatments. DA - 2007 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2007 T1 - Surface modification of titanium-based alloys TI - Surface modification of titanium-based alloys UR - http://hdl.handle.net/11427/4967 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/4967
dc.identifier.vancouvercitationCamagu ST. Surface modification of titanium-based alloys. [Thesis]. University of Cape Town ,Faculty of Engineering & the Built Environment ,Centre for Materials Engineering, 2007 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/4967en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentCentre for Materials Engineeringen_ZA
dc.publisher.facultyFaculty of Engineering and the Built Environment
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherMaterials Engineeringen_ZA
dc.titleSurface modification of titanium-based alloysen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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