Tensile Deformation Modeling of a Homogenized Cast Alloy 625: Effects of Large Grain Size

Abstract

In the present study, tensile deformation behavior of a coarse-grained (> 1 mm) cast alloy 625 has been investigated by applying empirical and physics-based models. The experimental stress-strain data of the alloy at different deformation temperatures are acquired from uniaxial tensile testing up to 700 °C. The plastic strain region of the alloy’s flow stress (σ) curve shows a significant deviation from the traditional Holloman equation. Parallelly, a distinctive hump in the strain-hardening (θ) curve is also observed after the initial steep drop. Dislocation density-based phenomenological modeling is adopted to ascertain the mechanisms governing plastic deformation of the alloy. The hump in strain-hardening curve is related to the combined effects of low-stacking fault energy of the material and large size grains, which led to deform the material with a smooth transition from restricted single slip at onset of plastic deformation to duplex slip and finally to multiple slips at later stages. As the deformation progresses, this transition results in a smooth exponential drop in the dislocation mean-free path. Transition in slip activity is confirmed through SEM and TEM studies. Further, when the deformation temperature increases, there is an increase in the rate of dynamic recovery and the rate at which single- → multiple-slip transition attains. The microstructural studies of the tensile-fractured samples indicate that the carbide/matrix and carbide/grain boundary interfaces play a crucial role in crack nucleation and propagation during the deformation. Notch tensile testing revealed that introducing a stress raiser would localize the strain and can cause dislocations to glide with a lowered initial mean-free path on multiple-slip systems from the very beginning of plastic deformation.