Effect of heat treatment on microstructure and mechanical properties of gas turbine intermetallic Ti-46Al-2W-0.5Si blades

In the frame of an international project COST, the effect of heat treatment on microstructure and mechanical properties of gas turbine blades prepared by investment casting from intermetallic Ti-46Al-2W-0.5Si (at.%) alloy was elucidated. Optimal parameters of the heat treatment, which minimise microstructural heterogeneity of the turbine blades and the parameters of kinetic equation for the grain growth were determined experimentally. The effect of long-term annealing on microstructural stability in different regions (lamellar, feathery and regions rich in gamma phase) of the turbine blades was defined. The parameters of kinetic softening equations were determined experimentally for these regions, which allow predicting the changes of mechanical properties of turbine blades during their projected service lifetime of 30000 h. Experimental results confirmed that mechanical properties of turbine blades with lamellar microstructure can be reliable predicted from simple microhardness measurements, which significantly simplifies material inspection after the heat treatment. The database of creep results, containing deformation characteristics of long term creep tested specimens (up to 10000 h) prepared from various types of cast components including the turbine blades, was elaborated. The confidential intervals of minimum creep rates were determined from large number of experimental creep results. These intervals are necessary for reliable structural calculations of blades before their implementation into stationary gas turbine engines. The effect of applied stress and temperature on minimum creep rate, time to 1% creep deformation and creep rupture time was determined. The parameters of kinetic equation, which expresses the dependence of minimum creep rate on the applied stress and temperature were determined. The mechanisms of creep deformation were revealed at operating temperatures and stresses of turbine blades. The effect of microstructure on initiation and creep damage propagation was described.

Publications

LAPIN, Juraj Creep behavior of a cast intermetallic Ti-45.2Al-2W-0.6Si-0.7B alloy. Scripta Materialia. Vol. 50, no. 2, 2004, p. 261-265.

LAPIN, Juraj – KLIMOVÁ, Alena – PELACHOVÁ, Tatiana Softening of a cast intermetallic Ti-46Al-2W-0.5Si alloy during annealing at 700-800°C. Scripta Materialia. Vol. 49, no. 7, 2003, p. 681-686.

LAPIN, Juraj – KLIMOVÁ, Alena On the grain growth in a cast intermetallic Ti-46Al-2W-0.5Si alloy. Journal of Materials Science Letters. Vol. 22, no. 18, 2003, p. 1275-1277.

LAPIN, J. – KLIMOVÁ, Alena Effect of heat treatment on the microstructure and mechanical properties of a cast intermetallic Ti-46Al-2W-0.5Si alloy. Metallic Materials. Vol. 41, no 1, 2003, p. 1-17.