Correlating Hot Deformation Parameters with Microstructure Evolution During Thermomechanical Processing of Inconel 718 Alloy

• DOI: 10.1007/s11661-019-05380-0
• Publication Date: 2019-08-13T14:23:35Z
• Authors: Chirag Gupta; Jyoti S. Jha; Bhagyaraj Jayabalan; Rajat Gujrati; Alankar Alankar; Sushil Mishra
• Keywords: 0203 mechanical engineering; 02 engineering and technology

Hot compression tests were conducted to determine the processing window for deformation of solutionized Inconel 718 over a range of high temperature and strain rate. Hot working map based on the dynamic material model was developed to establish the hot-processing regime. Maximum hot deformation efficiency within the processing regime is marked by the dynamic recrystallization, whereas an instability regime exhibits the highly deformed grains with shear bands. Further, selected deformed specimens were aged at 750 °C for 8 hours. Using electron back scattered diffraction and microhardness analyses, different microstructural properties such as grain size, twin fraction, grain average misorientation, and hardness were correlated. For deformed specimens, it was found that hardness is a function of misorientation and grain size. However, after aging treatment, hardness for all the specimens was found to lie in the range of 400 to 425 HV. Further, through transmission electron microscopy analysis, it was confirmed that deformed specimens are devoid of any precipitates while the deformed specimens followed by aging showed γ″ precipitates. Thus, the lack of correlation between the hardness and the grain size in the aged specimen was due to evolution of precipitates.