Pure gain

A new processing technique could reduce the cost and the amount of energy required to make titanium parts from powders by up to 50 per cent claim its developers.

This means titanium alloys could be made more cheaply for applications such as brake rotors, artificial joint replacements and armour for military vehicles.

Bill Peter, one of the developers of the process at the

(ORNL) in the US, said instead of using conventional melt processing to produce products from titanium powder, his group and several industry partners have developed a method that allows powders to remain in their solid form during the entire process.

'This saves a tremendous amount of energy, greatly reduces the amount of scrap and allows for new alloys and engineered composites,' he said.

The powder metallurgy process has been used to produce components for many years. However, titanium products have not widely been fabricated using these methods because of the high cost of conventional titanium powders.

To get powder metallurgy grade titanium powder, titanium must go through a hydride-dehydride (HDH) process or it has to be atomised by gas. Both of these methods produce powders that are expensive.

However, new low-cost titanium powders have enabled ORNL to develop these technologies for titanium.

The organisation has relied on the expertise of DARPA's Titanium Initiative Programme (DTI), which has developed methods that produce low-cost titanium powder at purity levels sufficient for powder metallurgy.

International Titanium Powder, one of DARPA's DTI project partners, developed a process that involves injecting titanium tetrachloride vapour into a stream of molten sodium. This causes a reaction to occur between the titanium tetrachloride and the sodium to produce titanium powder. With simple modifications of the process, it is also possible to make vanadium/aluminum titanium alloys.

Peter said the process runs at relatively low temperatures, does not require additional purification and produces high purity powder suitable for metallurgical processes with no waste.

The powder can then be used to produce net shape components with a variety of non-melt techniques, such as cold roll compaction of metal powder in a continuous sheet or coil.

This method has been used commercially for many years, but until recently titanium had not been commercially produced this way because of the high cost of conventional titanium powder.

The researchers at ORNL demonstrated that the low-cost titanium powder would work just as well as other metals with this technique. The team fed titanium powder through two counter-rotating rollers. The compressive stresses between them consolidated the material into continuous sheet.

The sheet was sintered and cold rolled to achieve full density and then softened by heat to acquire the desired microstructures and properties.

The ORNL team worked with the Department of Energy, the Department of Defence's Advanced Research Projects Agency and BAE Systems to demonstrate how the new powder could be used to produce a new low-cost titanium alloy door for the Joint Light Tactical Vehicle, a next-generation combat vehicle.

'By using a titanium alloy for the door, BAE Systems was able to reduce the weight of its vehicle while at the same time decreasing the threat of armour-piercing weapons,' said Peter.

The lightweight titanium alloy is also claimed to improve the operation of the door and increases mobility of the vehicle, making it even more useful to the military.

In the future, Peter and his colleagues expect lightweight corrosion-resistant titanium alloys to make their way into many other products, such as cars, which could benefit from the decreased weight and, he said, will be able to deliver improved fuel economy.