Activation Volume and Energy for Dislocation Nucleation in Multi-Principal Element Alloys

Abstract

Incipient plasticity in multi-principal element alloys, CoCrNi, CoCrFeMnNi, and Al0.1CoCrFeNi was evaluated by nano-indentation and compared with pure Ni. The tests were performed at a loading rate of 70 μN/s in the temperature range of 298 K to 473 K. The activation energy and activation volume were determined using a statistical approach of analyzing the “pop-in” load marking incipient plasticity. The CoCrFeMnNi and Al0.1CoCrFeNi multi-principal element alloys showed two times higher activation volume and energy compared to CoCrNi and pure Ni, suggesting complex cooperative motion of atoms for deformation in the five component systems. The small calculated values of activation energy and activation volume indicate heterogeneous dislocation nucleation at point defects like vacancy and hot-spot.

High-Temperature Nano-Indentation Creep Behavior of Multi-Principal Element Alloys under Static and Dynamic Loads

“…Therefore, the obtained activation volume for Ni was in the range for dislocation interaction while the lower value of V* for the two MPEAs indicates dislocation glide mechanism. Activation energy for dislocation nucleation is higher for a MPEA compared to pure metal [10]. Therefore, lower dislocation density in MPEAs favors dislocation glide over dislocation-dislocation interaction.…”

“…Therefore, probing the small-scale deformation behavior and local creep processes in MPEAs is critical in establishing their application worthiness. Nano-indentation technique has been widely used to characterize the small-scale deformation behavior of materials [9][10][11][12][13][14][15]. However, there are limited reports on the creep behavior of MPEAs using nano-indentation, and majority of the studies are at room temperature with a maximum load of 100 mN [16][17][18][19][20][21][22].…”

“…Here, we report the nano-indentation creep behavior of two MPEAs, namely CoCrNi and CoCrFeMnNi. These were chosen as model alloys with excellent mechanical properties [23] and a single-phase face centered cubic (FCC) microstructure [10,24]. Nano-indentation creep was studied under static and dynamic loads as a function of temperature and peak load.…”

Influence of load orientations with respect to twin boundaries on the deformation behaviors of high-entropy alloy nanocrystals

“…Second, the activation energy was one of the parameters to quantify the surface dislocation sources. 53 Compared with traditional metals with one principal element (e.g., austenitic steel, Au, and Ag), HEA (e.g., Al 0.1 FeCoNiCr) possessed lower dislocation activation energy because of the high lattice distortion in solid solutions, [54][55][56][57] which implied that the twinning dislocation nucleation from the surface was favorable. Furthermore, the local compositional inhomogeneity of HEA was severe due to the difference in atomic size and electronegativity.…”

High-Temperature Nano-Indentation Creep of Reduced Activity High Entropy Alloys Based on 4-5-6 Elemental Palette

“…In service, one of the essential design criteria for engineering components is the time-dependent deformation behavior (i.e., creep resistance). Macroscopic bulk compression or tension [10][11][12], micro-pillar compression [13,14], and nano-indentation technique [15][16][17][18][19][20][21] have been used to investigate the deformation behavior of materials in a wide range of length scales. Major discrepancies between the data obtained by nano-indentation and via conventional creep testing (i.e., compression/tension) have been reported [22,23].…”