Influence of heat treatments on plastic flow of laser deposited Inconel 718: Testing and microstructural based constitutive modeling

This work focuses on the experimental investigation into the heat-treatment influence on the plastic flow behavior of the laser metal deposited (LMD) Nickel-base superalloy Inconel 718 and the microstructural based constitutive modeling. The uniaxial compressive mechanical response of the LMD Inconel 718 superalloy was tested over wide ranges of temperature (298–1273 K) and strain rate (500 - ~12000/s). The tested samples were in three different heat-treatment conditions: as-deposited, direct-aged and aged after homogenization & solution (referred to as homogenized STA). Experimental results show that the differences of plastic flow behavior among these three samples were reflected in the amplitude of flow stress, strain hardening exponent, and the dependence on the temperature and strain rate. Based on micro observation, these differences were attributed to the evolution of grain geometry and volume fraction and size of γ" precipitates during heat treatments. A microstructural based constitutive model was developed. The thermal activated interaction between the moving dislocations and the precipitates was firstly proposed and embedded into the constitutive law. The influence of the heat treatments on the dynamic strain aging effect was attributed to the transition of interaction mechanism between dislocations and precipitates with the increasing precipitate size. This model was proved to be able to reproduce the plastic flow response of the LMD Inconel 718 alloy in different heat-treatment conditions over wide ranges of temperature and strain rate.