Novel joining for Ti and TiAl aeroengine components

Wu, Zhiwei (2010). Novel joining for Ti and TiAl aeroengine components. University of Birmingham. Ph.D.

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Experiments have been carried out to develop process-routes for bonding Ti6Al4V couples and Ti45Al2Mn2Nb1B couples using a combination of solid state diffusion bonding, powder sintering and brazing. The aim was to firstly produce air-sealed semi-bonds at moderate diffusion bonding conditions (i.e. low bonding temperature or low pressure) that did not downgrade the properties of the bonded components, and then complete the bonding by Hot-Isostatic-Pressing (HIPping) without the use of encapsulation.

In the first method, Ti6Al4V powder was used as interlayer when two Ti6Al4V blocks were diffusion bonded; and two TiAl powders, Ti48Al2Mn2Nb and Ti45Al2Mn2Nb1B, were used as bonding interlayer respectively when the Ti45Al2Mn2Nb1B couples were diffusion bonded. It was found that air-sealed bonds could be achieved only with the Ti45Al2Mn2Nb1B couples after the first-step bonding. HIPping and post-bond heat treatments were carried out to fulfill the bonding. Microstructural assessment and measurements of tensile strength and fatigue properties of the bonded samples were carried out and it was found that the bonded samples had properties comparable to those of the parent material.

In the second method, the brazing alloy TiCuNi-60 was used to seal the periphery of specially designed Ti6Al4V samples. Brazing was carried out in vacuum and the brazing time was optimised so that an air tight seal was produced, but the microstructural changes associated with liquid phase diffusion between the braze alloy and the Ti6Al4V were minimised. After brazing, the vacuum-sealed bonds were HIPped to produce fully bonded samples. The tensile properties of the bonds were shown to be comparable with those of the bulk material. A slight decrease in fatigue properties was found in the bonded samples, which was associated with inclusions on the interface caused by contamination before bonding.

Analysis of the factors controlling the bonding of nominally flat surfaces and of surfaces with powder interlayer has been carried out in order to explain the observations and the conditions required for successful low temperature, low pressure bonding defined.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
College/Faculty: Colleges (2008 onwards) > College of Engineering & Physical Sciences
School or Department: School of Metallurgy and Materials
Funders: None/not applicable
Subjects: T Technology > TL Motor vehicles. Aeronautics. Astronautics
T Technology > TN Mining engineering. Metallurgy


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