High-Entropy Alloy Coatings Deposited by Thermal Spraying: A Review of Strengthening Mechanisms, Performance Assessments and Perspectives on Future Applications

Abstract

Thermal spray deposition techniques have been well-established, owing to their flexibility in addressing degradation due to wear and corrosion issues faced due to extreme environmental conditions. With the adoption of these techniques, a broad spectrum of industries is experiencing continuous improvement in resolving these issues. To increase industrial-level implementation, state-of-the-art advanced materials are required. High-entropy alloys (HEAs) have recently gained considerable attention within the scientific community as advanced materials, mainly due to their exceptional properties and desirable microstructural features. Unlike traditional material systems, high-entropy alloys are composed of multi-component elements (at least five elements) with equimolar or nearly equimolar concentrations. This allows for a stable microstructure that is associated with high configurational entropy. This review article provides a critical assessment of different strengthening mechanisms observed in various high-entropy alloys developed by means of deposition techniques. The wear, corrosion, and oxidation responses of these alloys are reviewed in detail and correlated to microstructural and mechanical properties and behavior. In addition, the review focused on material design principles for developing next-generation HEAs that can significantly benefit the aerospace, marine, oil and gas, nuclear sector, etc. Despite having shown exceptional mechanical properties, the article describes the need to further evaluate the tribological behavior of these HEAs in order to show proof-of-concept perspectives for several industrial applications in extreme environments.

Strategic Selection of Refractory High-Entropy Alloy Coatings for Hot-Forging Dies by Applying Decision Science

“…These findings strongly support the idea that the top-ranked RHEAs excel in wear resistance, making them highly suitable for use as coating materials for hot-forging dies, which is evident in the WMoTaNb RHEA, which has a BCC crystal structure and exhibits a relatively high wear resistance (or low wear rate) at ambient and elevated temperatures [60]. The strengthening mechanisms elucidated in general in HEA coatings by Nair et al [61] provide good insights into understanding the strengthening of RHEAs in the present effort. However, it is worth noting that the top- 3 -Ta 13.1 -Ti 27.9 -V 4.5 -Zr 20.9 (ONS-BCC-796-2), and Al 7.9 -Hf 12.8 -Nb 23 -Ta 16.8 -Ti 18.9 -Zr 20.6 (ONS-BCC-796-1) are pertinent for generating data for other significant attributes, including wear resistance, fatigue (both thermal and mechanical), bonding compatibility with the substrate die material, oxidation resistance, potential reactions with the workpiece, cost-effectiveness, fabricability, and more.…”

Oxidation Behavior of FeNiCoCrMo0.5Al1.3 High-Entropy Alloy Powder

“…Cold-sprayed AlFeNiCoCr alloy retains the same BCC structure as was observed in the powder [26]. In contrast, in the plasma-sprayed coating of the same composition, the FCC phase is observed as the major one [27]. Despite high heating and cooling rates, which prevent the elements' diffusion development, factors such as high temperature, high oxygen concentration, and high specific surface of the powder inevitably lead to in-flight oxidation.…”

Microstructure and wear behaviour of AlCoCrFeNi-coated SS316L by atmospheric plasma spray process

“…At the higher sliding distance, the SWR is decreasing due to the formation of tribofilms. This acts as a self-lubricating layer protecting the surface [ 60 ]. The SWR at 400°C for the coated and annealed sample was 4.48% better than the coated sample before annealing.…”