Wear behavior of (Mo–Nb–Ta–V–W)C high‐entropy carbide

Abstract

Wear characteristics of an (Mo-Nb-Ta-V-W)C high-entropy carbide were investigated using ball-on-flat technique. The experimental material with a high relative density of 99.0%, single phase, average grain diameter of 10.7 μm, and nanohardness of grains 28.6 GPa was prepared by ball-milling and two-step field-assisted sintering. The tribological test was realized during dry sliding in air with the SiC ball as tribological partner at applied loads 5, 25, and 50 N. The microstructure, deformation, and damage characteristics were studied using scanning electron microscopy and confocal electron microscopy. The friction coefficient values during the test with 5 and 25 N were very similar and stable, with a value of approximately .4, whereas during the test with 50 N, it decreased from the value of .48-.42. The specific wear rate increased with increasing load from 3.71 × 10 -7 mm 3 /N m at 5 N to 2.59 × 10 -6 mm 3 /N m at 50 N. The dominant wear mechanism was mechanical wear with intensive grains pullout, fracture, and powder formation, without visible tribochemical reactions and tribo-layer formation. The wear rate decreased due to the created rolling contacts among the tribopartners thanks to the hard and spherical nanopowders present.

Lattice rigidity in high‐entropy carbide ceramics with carbon vacancies

“…High‐entropy carbides are the solid solutions of monocarbides, composed of five or more metal elements in roughly equal equimolar proportions and inherit the properties of the related monocarbides, which shows high thermal stability and high hardness 7–27 . High‐entropy carbides also have the feature of forming nonstoichiometric composition 16–23 .…”

Wear characteristics of dual‐phase high‐entropy ceramics: Influence of the testing method

“…According to the XRD results 25 , the investigated dual‐phase high‐entropy carbide/boride system consists of carbide and boride phases with lattice parameters a = 4.5413 Å for the FCC lattice of carbide and a = b = 3.1006 Å; c = 3.3670 Å for the hexagonal lattice of boride phases. These parameters are slightly different from the values measured and published for similar systems, which can be attributed to the difference in carbide/boride molar ratio and the difference of the concentration of transitional elements in carbide and boride phases in the investigated systems 16 …”

“…Detailed information concerning the material preparation is described in our recent publications. 25,26 The density of the system was measured by the Archimedes method in distilled water and the theoretical density was calculated based on the lattice parameters of the boride and carbide phases calculated using Rietveld analysis of the XRD patterns. The XRD analysis (Panalytical Empyrean, Cu K α radiation) was used to identify crystalline phases of the sintered ceramic and the Rietveld refinement was applied to determine the lattice parameters of boride and carbide phases in the dual system using a High Score Plus software.…”

Highly wear resistant dual-phase (Ti-Zr-Nb-Hf-Ta)C/(Ti-Zr-Nb-Hf-Ta) B2 high-entropy ceramics

“…The wear rate of the (Mo-Nb-Ta-V-W)C system at testing loads of 5 and 25 N shows approximately 10 times lower specific wear rate in comparison to the published (Hf-Zr-Ta-Nb-Ti)C system [28]. According to the results, it was caused by the significant difference in the grain boundary adhesion, which was lower for the (Hf-Zr-Ta-Nb-Ti)C system, resulting in very different wear mechanisms and wear rates.…”