Synergetic Enhancements on the Mechanical and Tribological Performance of Al₁₀Cr₁₇Fe₂₀NiV₄ Medium‐Entropy Alloys Induced by Nano‐Al₂O₃ Particles

Abstract

In a wide range of medium-entropy alloys (MEA, the mixing entropy of the alloy between 1 R and 1.5 R) and high-entropy alloys (HEA, the mixing entropy of the alloy exceeds 1.5 R), the multiprincipal elements HEA and MEA of the face-centered cubic (FCC) structure have attracted extensive attention ascribable to its prominent mechanical properties, [1] outstanding cryogenic property, [2] and wear resistance. [3] However, the mechanical properties of these FCC alloys are still deficient and there is still much room for improvement. To improve the mechanical performance of MEA, various strengthening mechanisms such as element precipitation [4,5] and the in situ formation of the second phase [6][7][8][9][10] have been studied in depth.HEAs, which were proposed by Yeh et al. [11] and Cantor et al., [12] first, have been paid much attention to and extensively studied by researchers in recent decades. Recently, it has been verified that adding Al 2 O 3 into FCC MEAs can make grain refinement and improve comprehensive mechanical properties. Zhao et al. [13] successfully prepared CrCoNi-Al 2 O 3 using mechanical alloying combined with the spark plasma sintering (SPS) method. The results exhibit that the nano-Al 2 O 3 particles are distributed uniformly in the CrCoNi matrix with ultrafine grain size (≤0.37 μm). The hardness of the composites with 2.5-7.5 wt% Al 2 O 3 reached a range of 521-603 HV. It manifests nanoparticle strengthening as a feasible strategy to improve the mechanical properties of MEA/HEA, which includes several strengthening mechanisms. In addition, the addition of Al can induce grain refinement, and the precipitation of favorable intermetallic compounds (such as Ni 3 Al) in some alloys, when combined with optimal thermodynamic treatments, will lead to significant hardening effects. [14] Al 0.4 FeCrCo 1.5 NiTi 0.3 reinforced by nano-Al 2 O 3 was synthesized successfully by mechanical alloying and SPS. It is found that nano-Al 2 O 3 promotes the formation of twins. [15] Hynek [16] et al. prepared CoCrFeNiMn HEA, which was strengthened in situ by mechanical alloying and in situ formation of nano-oxide dispersions. The microstructure analysis shows that the grain refinement rate of single-phase FCC alloy is about 50% in the presence of oxide.Moreover, among these properties, wear plays a significant role in the service life of metal parts with moving contact surfaces, for example, bearings and gears. Friction and wear may lead to local deformation and failure of materials during service, which have led to high demand for the development of wearresistant metal alloys. Compared with traditional commercial alloys, MEAs and HEAs with superior wear resistance result from superior hardness, oxidation resistance, and softening