Comparison of High Temperature Mechanical Behaviour and Microstructure of the New Gamma–TiAl8Ta with Gamma-TiAl8Nb Alloy
The high temperature creep and fatigue properties of two -TiAl base intermetallic alloys, for gas turbine components, have been investigated within the Integrated European project IMPRESS. The alloys contain 8% at. of Ta or Nb, respectively. The microstructure of both alloys was cross convoluted lamellar rather than the well known conventional lamellar, typical of the usual -TiAl. The microstructure of the Ta containing alloy was homogeneous in all the analyzed batches whilst that of the Nb alloy appeared significantly spread out from specimen to specimen. The creep properties of the alloys were investigated in the temperature range 700-850°C with applied stresses in order to have times to rupture up to about 3,000 h. The creep behaviour presented no steady state regimes, but only minima of the creep rates between significant decelerating and accelerating regimes. The minimum creep rates of the Ta alloy resulted to be significantly slower than the Niobium alloy at the same creep conditions. In low cycle fatigue at 650 and 700°C the Ta -TiAl showed longer lives than the Nb alloy, whilst the fatigue crack propagation rate in the same temperature range did not show any significant difference. Threshold values of stress intensity factor range were accurately measured at different R ratio. The microstructures of the two alloys were analysed by scanning microscopy in order to rationalise the different mechanical behaviour.
Pietro VINCENZINI, Cynthia POWELL, Marco VITTORI ANTISARI, Vincenzo ANTONUCCI and Fausto CROCE
G. Angella et al., "Comparison of High Temperature Mechanical Behaviour and Microstructure of the New Gamma–TiAl8Ta with Gamma-TiAl8Nb Alloy", Advances in Science and Technology, Vol. 72, pp. 40-45, 2010