Defu Li

Bio: Defu Li is an academic researcher. The author has contributed to research in topics: Dynamic recrystallization & Strain rate. The author has an hindex of 10, co-authored 14 publications receiving 469 citations.

Investigation on hot workability characteristics of Inconel 625 superalloy using processing maps

Abstract: Hot compression tests of the commercial Inconel 625 were performed in the temperature range of 950–1200 °C and strain rate range of 0.01–10 s−1. The flow behavior and processing maps were investigated using the corrected flow stress data to eliminate effects of the friction and adiabatic heating. The processing maps have exhibited a domain in the temperature range of 1100–1200 °C and strain rate range of 0.01–10 s−1 corresponding to the higher efficiency of power dissipation. Microstructural observations reveal that the full dynamic recrystallization (DRX) occurs in this domain, which is optimum processing window for hot working to obtain a homogeneous microstructure. DRX grain growth occurs in the temperature range of 1150–1200 °C and strain rate range of 0.01–0.1 s−1. In view of the refined and uniform grains obtained by hot deformation, the finish forming processing should be selected the deformation conditions in which the full DRX occurs without the grain growth. The small regimes of flow instability are noticed at temperature below about 970 °C at the different strains. The material undergoes flow instability manifesting as bands of flow localizations and high density deformation twins. In addition, it is found that the undissolved second-phase particles and carbides can promote the DRX processing and be helpful to restrict the DRX grain growth.

Hot deformation behavior and processing map of a typical Ni-based superalloy

Abstract: The hot compressive deformation behaviors of a typical Ni-based superalloy are investigated over wide ranges of forming temperature and strain rate. Based on the experimental data, the efficiencies of power dissipation and instability parameters are evaluated and processing maps are developed to optimize the hot working processing. The microstructures of the studied Ni-based superalloy are analyzed to correlate with the processing maps. It can be found that the flow stress is sensitive to the forming temperature and strain rate. With the increase of forming temperature or the decrease of strain rate, the flow stress significantly decreases. The changes of instability domains may be related to the adiabatic shear bands and the evolution of δ phase(Ni 3 Nb) during the hot formation. Three optimum hot deformation domains for different forming processes (ingot cogging, conventional die forging and isothermal die forging) are identified, which are validated by the microstructural features and adiabatic shear bands. The optimum window for the ingot cogging processing is identified as the temperature range of 1010–1040 °C and strain rate range of 0.1–1 s −1 . The temperature range of 980–1040 °C and strain rate range of 0.01–0.1 s −1 can be selected for the conventional die forging. Additionally, the optimum hot working domain for the isothermal die forging is 1010–1040 °C and near/below 0.001 s −1 .