Effect of oxygen diffusion hardening on fatigue resistance in Ti-6Al-4V alloys

Master Thesis


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University of Cape Town

The increased usage of titanium and its alloys in the aerospace industry and for biomedical applications has been attributed to its good strength to weight ratio, exceptional corrosion resistance and high melting point. In this research the titanium alloy that was focused on is the Ti-6Al-4V (by weight) alloy. With these good properties the alloys are also susceptible to poor tribological property behaviour. Surface engineering processes help improve these poor properties and one such process is known as Oxygen Boost Diffusion Hardening (OBDH). The OBDH process is a two-step process. The first step involves oxidation of the samples in air at elevated temperatures and the second step is carried out in order to diffusion treat the pre-oxidised specimens in a vacuum or argon environment. This was done using different oxygen and diffusion step temperatures and times. A comparison of the different fatigue lives after the treatments was made using the untreated specimen as the yardstick. The specimens were heat treated, in an oxidation furnace for the first stage and a controlled atmosphere furnace for the second stage. Thereafter, a rotational bending machine was used for the fatigue testing where fatigue failure data was obtained. For assistance in fully analysing the fatigue data; hardness tests, microstructural analysis and fracture morphology were undertaken and quantified.

Includes abstract.

Includes bibliographical references (leaves 106-110).