The main production process for titanium metal is known as the Kroll Process. In this process, the main ore, known as rutile, is treated with chlorine gas to produce titanium tetrachloride. This is then purified and reduced to a metallic titanium sponge by reaction with magnesium or sodium. The titanium sponge then undergoes an alloying and melting process. The process is a costly one, since it involves labour-intensive procedures.
Professor Deliang Zhang’s research has enabled him to develop a method of producing high-quality titanium alloy powders suitable for processing into commercial products such as combustion engine components.
Producing titanium-based alloy powders
The process uses aluminium and titanium dioxide powders along with other materials and involves the combination of several physical and chemical procedures. This alternative method of producing titanium-based alloys is potentially a major breakthrough due primarily to its low cost. Titanox Development Ltd has been established to scale up and commercialise the process.
One application being investigated by Professor Zhang’s team involves plasma-coating steel dies (used in the aluminium fabrication industry) with Ti-Al alloy powders. Exposure over time to molten aluminium causes surface damage to the dies. By plasma-coating them with a Ti-Al based alloy, the life of the dies is extended, resulting in lower production costs.
Another focus has been on the production of combustion-engine components such as valve rockers. By using Ti-Al based alloys, the overall weight of the engine is reduced, the wear life of the component is extended and the power to weight ratio in engine performance improved.
In the production process step involving the strong heating of the TiO2/Al mixture, it is essential to keep oxygen out of the system. The presence of oxygen, even in small amounts, can result in a brittle end product. The strong heating is carried out in an oxygen-free inert argon gas atmosphere.
Another problem encountered is in producing components with no cavities remaining within the structure. The presence of cavities affects mechanical properties such as ductility. Powder forging techniques are being developed to ensure that the final product has maximum density with no cavities present.
Nature of science
Scientists often work collaboratively across a wide range of disciplines. The materials engineering field requires the input of knowledge from specialist disciplines such as chemistry, physics, mathematics, mechanical engineering and technical support.