Sharif Digital Repository

Two-internal variable thermodynamics model is presented to investigate the evolution of microstructure and flow stress during severe plastic deformation. Previous studies have shown that due to heterogeneous distribution of dislocations during severe plastic deformation, the use of multivariable models is needed. In this regard, a two-internal variable model is presented. In the present paper, the dislocation densities in the subgrain boundaries and interiors are considered as internal variables. The model uses general laws of thermodynamics and describes the evolution of the dislocation densities on the basis of parameters such as the self-diffusion activation energy and the stacking fault... 

Recent investigations have shown that the steady state grain size of severely deformed materials is dependent on the stacking fault energy. In this paper, a model is presented to investigate such a dependency which uses thermodynamics based calculations. The present model shows that the relationship between the steady state grain size and the stacking fault energy of material is in power law form, directly. Furthermore, the model shows that the steady state grain size has an exponential relationship with the self-diffusion activation energy and a decrease in the self-diffusion activation energy increases the steady state grain size. The model predictions are in good agreement with the... 

In this paper, results of an investigation on strain hardening mechanisms of aged AEREX350 alloy during room temperature compression testing are reported. TEM studies were conducted on commercial samples aged at 850 °C both before and after deformation in a strain range of 0.15-0.27. It was found that only coherent γ′ precipitates with L12 structure formed in these samples prior to deformation. TEM studies also showed twin intersections in the deformed samples. Based on these observations, it is suggested that the high strain hardening rate of the aged material in this strain range is mainly related to the formation of intersecting deformation twins. This is attributed to the decrease in the... 

True stress vs. true strain responses of Cu-6 wt.% Al and Cu-12 wt.% Mn alloys are presented. While Cu-6 wt.% Al alloy shows the typical mechanical response of low stacking fault energy alloys, the Cu-12 wt.% Mn alloy behaved similarly to medium to high stacking fault energy alloys. These findings clearly show that while short-range ordering triggers slip planarity, it has a minor effect on total dynamic recovery of these copper alloys  

Results of an investigation on the evolution of microstructure during simple compression testing of two face-centered-cubic (fcc) polycrystals, IN625 superalloy and 316L stainless steel, are reported and a review on the existing data related to the uniaxial deformation of fcc polycrystals is presented. It is found that while a number of fcc polycrystals show linear hardening behavior, the evolution of the underlying microstructure may be quite different. It is argued that, in contrast to the current belief, deformation twinning may not be the sole cause of linear hardening in low stacking fault energy (SFE) fcc polycrystals. It is suggested that, due to the requirement of slip system change... 

Simple compression and microscopy techniques were employed to characterise the microstructural origin of the deformation behaviour of nickel base superalloy IN625 during large strain testing. The alloy exhibited a four-stage strain hardening response similar to that previously reported for low stacking fault energy face centred cubic alloys. At strains lower than about -0.06 (stage A), a falling regime of the hardening rate was observed. This stage was followed by a second stage (stage B) of slow increasing hardening rate, which was found to be coincident with the formation of Lomer-Cottrell locks. The second falling regime of strain hardening (stage C) was seen in the strain range of -0.25...