B Research Program B: Titanium
Program Leader: Professor Graham Schaffer - The University of Queensland
This program is aimed at improving the processing and development of titanium alloys, particularly through the use of powder and equal channel angular extrusion. A summary of each project and key strategic targets is outlined below:
• Project B1: Hydrogenated Ti powder pre-forms
  The essence of this project is to introduce into, or leave in, hydrogen during the early stages of processing. Once a compact product is attained a final pre-treatment is employed during which time hydrogen is removed and the final properties are established.
The project aims to establish, for the two most common Ti alloys (CP-Ti and Ti-6Al-4V): the degree to which hydrogen influences the development of the ductility of the green product during thermal pre-treatment; the extent to which hydrogen improves ductility during strain compaction; the degree to which hydrogen improves properties of annealed compacts; the nature of the processing constraints imposed by the need to remove hydrogen and the need to keep times low; the optimal level of hydrogen for productivity and cost taking all of the above into account.
• Project B2: Equal Channel Angular Extrusion (ECAE) of aerospace Ti alloy
  New titanium production technologies that have the potential to transform the light metals industry all produce powders as a final product. These powders need to be consolidated to make either components or feedstock (such as billet) for other secondary manufacturing processes (such as forging). The aim of this project is to produce such forging billets directly from powder at low temperatures. This will be achieved using equal channel angular extrusion with back pressure. Strategic design targets for the project include:
• Decreasing the cost of manufacturing process by excluding the evacuating stage, soft cans use and removal of the sintering stage for forging stock.
• Minimising contamination by gases by decreasing the temperature of compaction.
• Reducing porosity by activating physical mechanisms at lower temperatures.
• Producing bar from HDH Ti-6Al-4V powder with a relative density of 98-99% and green strength above 750 MPa at temperatures below 400OC.
• Project B3: Ti powder processing
  The aim of this project is to develop new titanium alloys and processing strategies for the net shape processing of components using the blended elemental powder metallurgy (PM) and powder forging (PF) approaches. The project contains three vertically integrated streams: (1) the analysis of titanium powder surface chemistry; (2) the understanding and enhancement of the sintering of titanium and (3) the development of forging strategies to produce fully dense components from sintered performs.
The suitability of powders for sintering and subsequent processing are determined by examination of the following characteristics which affect their consolidation: chemical composition; phase composition and impurity level; size distribution, shape and roughness of the particles; number and size distribution of pores; state of surface and internal stress; concentration of defects; presence of surface films and adsorbed impurities; and state of agglomeration. The maximised sintering response will be achieved by (1) optimising the composition; (2) identifying and testing potential additives that may activate the sintering of titanium; (3) microalloying to manipulate the liquid phase sintering response and (4) sintering by partially melting pre-alloyed powders, a process known as supersolidus liquid phase sintering. Forging is examined using a constraining back pressure to control material flow throughout the forging strike, increasing pore closure and decreasing the tendency for surface cracking.
• Project B4: Ti alloy development
  Property/microstructure relationships are critical to the behaviour of Ti alloys. For any particular alloy the microstructure may be tailored to meet the specific requirements of the end application. It is recognised, however, that Ti alloys in general suffer from quench sensitivity and only a small number are considered to be deep hardenable as a consequence. Currently, Ti alloys are deemed to be deep hardenable if the strength can be maintained at 95% of the UTS at a thickness of 100mm. There is a real need for this to be improved so that thicker section components can be produced.
This project aims to address the problem of deep hardenability, looking at the fundamental mechanisms which control this behaviour. Once these have been identified, selected commercial alloys will be examined with a view to improving their hardenability. The project involves:
1) Review of current literature in the field, and identifying microstructural features which may strongly affect deep hardenability.
2) "Reverse engineer" an alloy considered to be deep hardenable, taking particular note of the contributions from those features identified in 1.
3) Take selected features from 1 and examine their role in detail in a systematic way, using ideal alloys rather than commercial compositions.
4) Apply the results to a commercial alloy.