Evaluation of ingots and alpha-extrusions of gamma alloys based on Ti-45Al-6Nb

Three gamma TiAl alloys having compositions within the range of Ti-45Al-6Nb-0.4C-0.2Si-xB-yCr-z(W+Hf) were produced into 6.3 cm diameter ingots by the ingot-skull melting (ISM) technique. Billets from the ingots were hot-worked by the so-called 'alpha extrusion» process that yields in situ lamellar structures. Isothermal aging experiments at 900 and 1000 °C were conducted on the extruded material to investigate the microstructural stability and consequential strength variations. Microstructures, their evolution and variation, and compositional distribution for each processing step were characterized using electron microscopy, X-ray mapping, micro probe analysis and DTA measurements. The effect of aging on strength variation was detected and analyzed through micro-hardness measurements and their relationships with yield strength. The preliminary results, including oxidation measurements, are reported and analyzed as a function of alloy composition.