A first approach on the assessment of the creep behavior of MoTaNbVxTi high entropy alloys by indentation testing

Abstract

MoTaNbV x Ti refractory high entropy alloys were tested with dynamic indentation technique in order to assess their creep behavior. The loading rate was kept constant and three indentation depths were applied. It was found that, by increasing the indentation depth and the V content of the alloys, the stress exponent was reduced. This reduction was associated with the maximum applied stress at the peak load before the holding period and the increase of lattice distortion parameter with increasing the V content.

The Advanced Assessment of Nanoindentation-Based Mechanical Properties of a Refractory MoTaNbWV High-Entropy Alloy: Metallurgical Considerations and Extensive Variable Correlation Analysis

“…One final observation that must be mentioned is the fact that serrations, if present, are found in most of the cases associated with the lower loading speeds. This observation is in agreement with other experimental efforts [5][6][7][8][9][10][11]22], according to which the most important factor influencing the formation of serrations is the strain rate. Various research efforts have shown that high strain rates during the loading stage result in the absence of serrations, i.e., lack of creep deformation during loading [5][6][7][8][9][10][11].…”

“…This is expected since the more prolonged the time, the more time for the available dislocations to move and provide plastic flaws, i.e., plastic deformation. Similar observations can also be found in other experimental efforts [8,9,22].…”

“…Since this zone is expanded and in conjunction with the fact that the time is considerably increased, the mobile dislocations within this zone, can move more extensively to provide plastic deformation. Karantzalis et al [22] and [2,5,9,11,12,34] also reported similar observations concerning the effect of the preset depth.…”

“…To evaluate the creep response of the system via nanoindentation, the mathematical frameworks referenced in studies [5,12,22,23] were utilized. These frameworks detail the calculations necessary for understanding the system's behavior under specific conditions.…”

Development and characterisation of new high entropy alloy systems of dual and/or multiple phases

“…This means that the deformation rate, in turn, does not show much dependence on the applied load, and as such, the stress exponent decreases. Based on the literature [170,173,174,227], these calculated values are attributed to dislocation sliding as the dominant mechanism concerning the dislocation movement, while for higher values, dislocation climbing plays also a supportive role.  In the case of the eutectic micro-constituent, the formulation of a mechanism that would explain the changes in the stress exponent values is very tricky.…”