Titanium is a highly desirable light alloy because of its high strength to weight ratio, corrosion resistance, biocompatibility and creep resistance. The allotropic transformation allows a range of thermo-mechanical treatments and a variety of tailored properties. Despite the benefits of titanium, widespread use has been limited due to the high cost of extracting and fabricating the material. Current titanium production via the Kroll process involves an inefficient batch process. New methods in extractive metallurgy such as the FFC Cambridge process have been developed. These new processes have the potential to produce costeffective titanium as well as produce high purity powder. Thus, there is an increased interest in the area of titanium powder metallurgy, where net-shape parts are produced from metallic particulates.
Liquid phase sintering has proven to be an effective method of producing high density parts in many metallic systems. The current body of research in the area of titanium liquid phase sintering is limited. In this thesis, the role of silicon and nickel additions in titanium liquid phase sintering has been investigated. The densification behaviour was observed through the use of dilatometry and metallography.
This thesis has shown that the formation of a liquid phase is detrimental to densification. Very large pores, termed ‘giant pores’, were observed after liquid phase sintering with silicon additions. Furthermore, at low liquid fractions dilatometry behaviour termed ‘serrated expansion’ was observed, whereby samples produced a large expansion event interspersed with sharp contractions. Both effects can be attributed to gas production.
The expansion behaviour and the giant pores were found to be independent of wax additions and also occurred during Ti-Ni liquid phase sintering. It is proposed that dissolved hydrogen in the titanium powder is the source of the gas production. Hydrogen dissolution may have occurred during prior manufacturing of the powder. An upper limit estimate of the pressure driving the formation of giant pores is 24 MPa.