Nanoindentation testing as a powerful screening tool for assessing phase stability of nanocrystalline high-entropy alloys

Abstract

The equiatomic high-entropy alloy (HEA), CrMnFeCoNi, has recently been shown to be microstructurally unstable, resulting in a multi-phase microstructure after intermediate-temperature annealing treatments. The decomposition occurs rapidly in the nanocrystalline (NC) state and after longer annealing times in coarse-grained states. To characterize the mechanical properties of differently annealed NC states containing multiple phases, nanoindentation was used. The results revealed besides drastic changes in hardness, also for the first time significant changes in the Young's modulus and strain rate sensitivity. Nanoindentation of NC HEAs is, therefore, a useful complementary screening tool with high potential as a high throughput approach to detect phase decomposition, which can also be used to qualitatively predict the long-term stability of single-phase HEAs.

Mechanical Properties of Nanostructured CoCrFeNiMn High-Entropy Alloy (HEA) Coating

“…The average hardness and elastic modulus were calculated according to the Oliver-Pharr method from the loaddisplacement curves as an average from 49 indents. An average of 49 indents on the film results in an elastic modulus of 176.8 ± 2.4 GPa and a hardness of 6.8 ± 0.6 GPa, of which the hardness is much higher than its bulk counterpart (Lee et al, 2016;Maier-Kiener et al, 2017) as shown in Figure 5a. The increase of hardness may due to nanograined microstructure and Physical Vapor Deposition (PVD) technique, since melting bulk HEA materials of traditional approach exhibit very large grain sizes in the micrometer-scale.…”

Synthesis and characterization of multicomponent (CrNbTaTiW)C films for increased hardness and corrosion resistance

“…The results show that incorporation of low amounts of carbon results in an increase in strength due to precipitation and grain boundary hardening. While bulk refractory high entropy alloys have been studied in detail by experimental [6][7][8][9][10][11] and computational [12][13][14] material science, there are only a few studies published on the addition of carbon to HEAs based on strong carbide formers such as the early transition metal in group 4 and 5 [5,15,16]. Braic et al have shown that (TiZrNbHfTa)C with a B1 structure with C in the octahedral sites can be synthesised by co-sputtering in a reactive atmosphere [15].…”

Phase Decomposition of a Single‐Phase AlTiVNb High‐Entropy Alloy after Severe Plastic Deformation and Annealing

“…In fact, only a minority of systems are true single phase alloys with typically face‐centered‐cubic (fcc) or body‐centered‐cubic (bcc) structures . Even in that small subset, some alloys decompose to a multi‐phase structure upon annealing, see, for instance, ref . An often proposed potential field of application for HEAs in future is the high‐temperature regime due to their occasionally outstanding specific yield strengths and their proposed sluggish diffusion behavior .…”