M. Stockinger, Böhler Schmiedetechnik GmbH & Co KG, Kapfenberg, Austria; C. Stotter, C. Sommitsch, Christian Doppler Laboratory of Materials Modelling and Simulation, University of Leoben, Leoben, Austria; E. Kozeschnik, Christian Doppler Laboratory for Early Stages of Precipitation, Graz University of Technology, Graz, Austria
Aerospace gas turbine discs operate in an environment of relatively high stresses caused by centrifugal forces and elevated temperatures. These severe conditions require materials with excellent high temperature properties. Recently, the new alloy Allvac 718PlusTM was developed to further increase the service temperature by at least 55°C while retaining a comparable processability to alloy 718. The properties of gas turbine disks are sensitive to the microstructure, e.g. grain size and precipitations, which depend on the processing history. The interest in microstructure modelling has gained considerable momentum over the past two decades. However, most of the published models are of Avrami type, which have no predictive capabilities with regard to second-phase precipitation. In order to obtain an adequate final microstructure and hence optimized mechanical properties it is necessary to predict the precipitation history as a function of temperature. The results of the simulations are fed into a physical-based microstructure model.In this paper, we present experimental results on the δ-phase precipitation kinetics in Allvac 718PlusTM. Based on this data, computer simulations were performed using the precipitation kinetics module of the software package MatCalc. Experimental data and simulation results, i.e. time-temperature–precipitation (TTP) diagrams, were compared in order to calibrate the precipitate-matrix interfacial energy. Annealing experiments were performed and the fraction of δ-phase precipitates was determined by means of quantitative optical microscopy. Additionally, differential scanning calorimetry (DSC) investigations were carried out to determine the solution temperature of the δ-phase. The results of the calculations obtained using a temperature-dependent interfacial energy were in good agreement with the experiments.
Summary: Aerospace gas turbine discs operate in an environment of relatively high stresses. The properties of gas turbine disks are sensitive to the microstructure, i.e. grain size and precipitations, which depend on the processing history. Computer simulations of the δ-phase kinetics were performed using the precipitation kinetics module of the software package MatCalc and were compared to experimental data using quantitative optical microscopy and DSC methods. The results of the calculations obtained using a temperature-dependent interfacial energy were in good agreement with the experiments.
