| Compared with the traditional nickel and titanium based high-temperature alloys,TiAl-based alloys are characterized by the low density, high specific strength, andrelatively good combination properties at elevated temperature. Due to their excellentproperties, TiAl-based alloys have become the most potential candidated material inlightweight high-temperature structural materials for aeroengine. The improvement ofductility at room temperature and hot workability is the premise of their industrialapplications. In the present work, hot compression tests and microstructureexaminations were employed to investigate the hot deformation behavior,microstructure evolution and dynamic recrystallization (DRX) of PM Ti-47Al-2Nb-2Cralloy. In order to optimize the hot working parameters and effectively control themicrostructures and properties of alloys， the internal relationship of processingparameters, dynamic mechanical behavior, microstructure evolution and hot workabilitywere systematically revealed. The research results will offer the theoretical basement forthe hot working production of high-performance TiAl-based alloys components.The flow stress characterizations of PM Ti-47Al-2Nb-2Cr alloy were studied byisothermal hot compression. By using Arrhenius-type constitutive model consideringthe strain compensation and artificial neural network model, the constitutiverelationship models of PM Ti-47Al-2Nb-2Cr alloy were developed respectively. Thecomparative evaluation of the Arrhenius-type constitutive model and the ANN modelwas carried out.Furthermore, the microstructure observation results showed that dynamicrecrystallization (DRX) is the main softening mechanism during the deformationprocess of PM Ti-47Al-2Nb-2Cr alloy. The deformation temperature, strain rate andstrain have obvious effects on the DRX behavior. The finer dynamically recrystallizedgrains will improve properties of the alloy. The relationship between the DRX grainsize and parameter Z is developed based on Sellars model.Processing maps on the basis of dynamic material model (DMM) and Prasadinstability criterion at different deformation conditions were established. The optimalhot working domains of PM Ti-47Al-2Nb-2Cr alloy with completely dynamicrecrystallization microstructure is1025-1075℃/0.001-0.004s1. The regime ofinstability mainly appears in the strain rate range of0.01-0.1s1, and increases with the increase of strain, which is in accordance with the real cracking tendency of compressedspecimen. Therefore, the processing map can be used to predict the microstructures andoptimize the deformation process of PM Ti-47Al-2Nb-2Cr alloy. |
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