Study of the microstructure and texture heterogeneities of Fe–48wt%Ni alloy severely deformed by equal channel angular pressing

Abstract

A Fe-48wt%Ni alloy was processed by severe plastic deformation using equal channel angular pressing process. A stacking of 9 sheets was introduced and pressed up to two passes into die with an inner angles of Φ=90º and outer arc of curvature ψ= 17° at room temperature following route A. The same material in bulk form was also ECAPed up to one pass. The microstructure and the texture were investigated by means of electron backscattered diffraction and X-ray diffraction, respectively. To evaluate the mechanical response, Vickers microhardness was carried out. The given analyses concern the asreceived sample, the peripheral and the central plates of the pressed stacks and the upper, the middle and the lower parts of the pressed bulk material. The deformation was heterogeneous and variations in texture and microstructure, resulting from different efficiencies in the shearing process, were locally noted. For the stacks samples, the microstructure evolved from equiaxed grains of 9 μm with high fraction of high-angle grain boundaries (around 90%) to a heterogeneous fine grain structure with an average grain size of 3 m after two passes. On the contrary, for the bulk sample, the evolution was 2 to a banded structure after one pass. Results of mechanical property show that microhardness increased significantly from 147 Hv before deformation to mean values of 244 (after one pass) and 235 Hv (after two passes) for the bulk and stacked samples, respectively. The Hall-Petch effect and dislocation density were evaluated as the most responsible in material strengthening.

The Influence of A Cross-Channel Extrusion Process on The Microstructure and Properties of Copper

“…A similar behavior was observed by Lachhab et al [59] for an ECAP-ed Fe-48Ni (wt. %) alloy, where the microhardness increased by nearly two times after the second passes.…”

Facing the Issues of Sheet Metal Equal‐Channel Angular Pressing: A Modified Approach Using Stacks to Produce Ultrafine‐Grained High Ductility AA5083 Sheets

“…Figure 1 schematically shows the principle of processing stacked sheets in an ECAP die with a square cross‐section, highlighting two different methods that can be applied to completely fill the entrance channel. Method 1, proposed by Lachhab et al, [ 24 ] is characterized by stacking the appropriate number of sheets (depending on the sheet thickness) needed to completely fill out the channel, see Figure 1a. However, as some clearance is needed for inserting a billet (or stack of sheets) into the channel, and because loading during processing leads to an elastic expansion of the die, some additional clearance is generated during the ECAP process and this results in buckling of the sheets, as shown in Figure 1b,c.…”

“…The stacked sheets approach in principle represents a promising alternative without these drawbacks because thin sheet materials can potentially be processed in conventional, well‐developed ECAP dies. [ 23,24 ] However, the results presented in the study by Lachhab et al [ 24 ] on processing a stack of 9 Fe–48 wt%Ni sheets also show that stacks may be prone to sliding between individual sheets, which further results in heterogeneous shear deformation with superimposed bending, in correspondingly heterogeneous grain sizes, mechanical properties, and textures that ultimately also depend on an individual sheet's position in the stack. Obviously, further improvements are needed to fully exploit the potential of the stacked sheets approach and to meet an essential requirement: providing a homogeneous and well‐defined shear deformation throughout the stack of sheets.…”

Progress in High-Entropy Alloy Performance Enhancement

“…Traditional alloy materials are predominantly composed of iron, cobalt, nickel, titanium, and similar metals [1][2][3][4]. The practice of enhancing alloy performance by adding a small amount of other elements to one or two principal elements, although superior to coatings made from a single metal, is not without its challenges.…”