Low-pressure turbine blades made of titanium aluminium The emergence of a new class of alloys based on the gamma phase of titanium-aluminium (gamma-TiAl) systems brings the promise of unprecedented improvements in aircraft engine performance. EU-funded researchers developed technology to address difficulties in machining due to brittleness. Energy © Thinkstock Among the biggest obstacles to overcome have been those associated with the poor wrought processing of ingot forms. Such difficulties are not unexpected considering the restricted temperature range for deformation processing as well as the limited hot-workability that gamma-TiAl alloys exhibit. Therefore, isothermal forming processes have been favoured so far. A fair amount of success has been achieved in increasing the deformation window by the addition of beta-phase titanium into the microstructure of gamma-TiAl alloys. With EU funding of the project DATACAST (Development of a low cost advanced gamma titanium aluminide casting technology), researchers developed a niobium and molybdenum-containing gamma-TiAl alloy. The trademarked TNM alloy solidifies through beta-phase and exhibits an adjustable beta/B2 (the ordered phase of beta at low temperatures) phase volume fraction. Thanks to the high-volume fraction of beta-phase at elevated temperatures, the new alloy can be forged using conventional equipment with minor and inexpensive modifications. DATACAST members focused on vacuum arc melting (VAR) and plasma arc melting (PAM) ingot-processing technologies. They demonstrated the feasibility of converting the resulting ingots to small-size forging stocks through skull melting using VAR or vacuum induction melting. These can then be used to produce permanent moulds with centrifugal casting followed by hot isostatic pressing and machining. Extensive investigations of the homogeneity of single VAR- and PAM-melted ingots showed their suitability for use as consumable VAR skull melter electrodes. The ingots can be further homogenised in the skull melter to obtain specified chemical compositions. Work on the rotational speed of the casting wheel, pouring time and crucible tilting curve has improved the pouring of slugs via centrifugal casting. DATACAST has resulted in technology to convert TiAl-based ingots into forging stocks that meet the stringent requirements for high-quality materials needed to manufacture low-pressure turbine blades. TiAl is lightweight and resistant to high temperatures, making it an ideal material for aircraft engine components. TiAl blades will enable savings in weight and fuel consumption, thus achieving reductions in carbon dioxide emissions. Keywords Turbine blades, titanium aluminium, aircraft engine, wrought processing, ingot, DATACAST
