Elastic and plastic deformations in a high entropy alloy investigated using a nanoindentation method

Abstract

We employed instrumented indentation technique to study the elastic and plastic deformations in a face-centered cubic (fcc) high-entropy alloy NiFeCoCrMn. Single-crystal Ni was also examined for direct comparison. Tests were carried out using indenters with different tip radii to investigate the effect of indented volume on deformation processes. It was found that when the tip radius increased, the shear stress required for the occurrence of indentation pop-in decreased, which was attributable to a higher probability to find dislocations under a larger tip radius. We proposed a statistical model to describe the results quantitatively. In the plastic region, NiFeCoCrMn was much stronger than Ni, presumably resulted from a large lattice distortion in the multicomponent NiFeCoCrMn alloy. We found that the response of both materials at large indentation depth could be described by the classical Nix-Gao model, but when the indentation depth was shallow, the indenter tip must be treated as a sphere and Swadener's model offered a better description. In any event, it was necessary to introduce a scaling factor f to describe the effective stressed volume underneath the indenter tip to compensate for the overestimated hardness values. A map of indentation pressure against dislocation density was also summarized in this study.

Atomic-scale analysis of nanoindentation behavior of high-entropy alloy

“…In addition, the occurrence of a phase transformation from the FCC structure to the BCC structure is observed in Fig. 8(a), qualitatively consistent with indentation experiments of HEA [Wu et al, 2016]. Figure 10 shows the dislocation structures in the plastic zone of FeCrCuAlNi HEA indentation for different indentation depths, demonstrating the generation and reaction of dislocations.…”

Materials and corrosion trends in offshore and subsea oil and gas production

“…In such instances, the indentation starts with an elastic loading that follows the Hertzian contact model. [100][101][102][103][104][105][106] As the shear stress below the tip in the volume of the material approaches the theoretical stress required for homogeneous dislocation nucleation, a sudden jump, i.e., the so-called pop-in, in the displacement occurs. The pop-in marks the transition from elastic to elastoplastic deformation in a perfect crystal.…”

Structure and Phase Composition of a W-Ta-Mo-Nb-V-Cr-Zr-Ti Alloy Obtained by Ball Milling and Spark Plasma Sintering

“…The interest in these alloys is due to unique combinations of mechanical properties that they can offer when properly designed. Research in this area is aimed at finding new promising compositions [1][2][3][6][7][8][9], characterizing the microstructure and mechanical properties [10][11][12][13][14][15][16], studying the mechanisms of plastic deformation [4,17], or determining the phase composition and phase stability of the alloys [18][19][20][21][22][23][24][25][26][27][28][29].…”