Microstructural and mechanical study in the plastic zone of ARMCO iron processed by ECAP

Abstract

Plastic deformation of ARMCO iron processed by ECAP up to a maximum equivalent strain of sixteen (i.e., 1, 4, 8, and 16 ECAP passes) following route Bc was investigated by analyzing its microstructure and the stress-strain curves obtained after tensile tests at different levels of deformation. Three values of deformation (two in the plastic region taking into account the modified Crussard-Jaoul analysis and one after failure) were considered. Fractions of LAGB and HAGB, grain size and grain aspect ratio were calculated and compared for the different ECAP passes and tensile deformation levels. The dislocation density evolution calculated by the Bergström model for both the tensile curves and the ECAP curve showed a higher increase in the amount of dislocations during the initial stages of deformation than at higher values of deformation due to higher probabilities of dislocations annihilation. The strain hardening exponents calculated via the Bergström model for each ECAP pass shows that there is a continuous decrease in the strain hardening capacity until the eighth pass where a small increase with a subsequent stabilization was found. The dislocation densities calculated by the Estrin model presented a good correlation with values reported in bibliography for iron especially with those calculated by X-ray diffraction.This latter model predicted well the strain hardening evolution for stages 2 III, IV and V for ARMCO iron processed by ECAP, where the main increments in hardening for stages IV and V were coming from the cell interiors.

Severe Plastic Deformation of Fe-22Al-5Cr Alloy by Cross-Channel Extrusion with Back Pressure

“…The microhardness of the tested alloy increases by an average of 10% (Figure 11b). This behavior is typical for metallic materials, especially on iron, subjected to deformation by SPD techniques [50,54,55,56,57]. Generally, the level of hardness is increased with the increase in the number of passes and the complexity of the stresses.…”

“…With further deformation (increasing the number of passes) most of the LAGB evolve into HAGB leading to homogeneity and an ultrafine-grain material, as results of continuous dynamic recrystallization [22,54,55].…”

Effect of strain energy on the grain growth behaviour of ultrafine-grained iron-chromium alloy by equal channel angular pressing

“…The abnormal grain growth in FCC material shows small journal.ump.edu.my/jmes ◄ fractions of grains growing predominantly, replacing the other smaller, Phenomenologically, this mode of grain growth can be regarded as discontinuous recrystallization [7]. The material processed by ECAP is considered by high internal stresses, which are related to both high dislocation densities and non-equilibrium grain boundaries [1,[26][27][28]. Microstructure with high HAGB fraction have been recommended as being basically resistant to discontinuous recrystallization regardless of an apparently high stored energy, and only the uniform grain growth tends to operate frequently in such structures [29,30].…”

Dynamic Steady State by Unlimited Unidirectional Plastic Deformation of Crystalline Materials Deforming by Dislocation Glide at Low to Moderate Temperatures

“…The extension of the stress-strain analysis provided by ECAP does not change the most important conclusions reached from studies in the "large strain" range: Stage IV carries on toward its asymptotic limit without signs of any Stage V. Figure 6 shows results for commercially pure Cu, Ni, Fe, and Ti deformed by ECAP at room temperature (data from refs. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]). Although there is much scatter in the results (inherent to the ECAP process and its analysis: the plastic heterogeneity of the deformed samples, different variants of the strain path used by different authors, testing by tension or by hardness), it seems clear that an apparent saturation of the flow stress occurs near a VME strain of 7.…”