High-Entropy Coatings (HEC) for High-Temperature Applications: Materials, Processing, and Properties
18 May 2022-Coatings-Vol. 12, Iss: 5, pp 691-691
TL;DR: High-entropy materials (HEM), including alloys, ceramics, and composites, are a novel class of materials that have gained enormous attention over the past two decades as mentioned in this paper .
Abstract: High-entropy materials (HEM), including alloys, ceramics, and composites, are a novel class of materials that have gained enormous attention over the past two decades. These multi-component novel materials with unique structures always have exceptionally good mechanical properties and phase stability at all temperatures. Of particular interest for high-temperature applications, e.g., in the aerospace and nuclear sectors, is the new concept of high-entropy coatings (HEC) on low-cost metallic substrates, which has just emerged during the last few years. This exciting new virgin field awaits exploration by materials scientists and surface engineers who are often equipped with high-performance computational modelling tools, high-throughput coating deposition technologies and advanced materials testing/characterisation methods, all of which have greatly shortened the development cycle of a new coating from years to months/days. This review article reflects on research progress in the development and application of HEC focusing on high-temperature applications in the context of materials/composition type, coating process selection and desired functional properties. The importance of alloying addition is highlighted, resulting in suppressing oxidation as well as improving corrosion and diffusion resistance in a variety of coating types deposited via common deposition processes. This review provides an overview of this hot topic, highlighting the research challenges, identifying gaps, and suggesting future research activity for high temperature applications.
TL;DR: In this article , a review summarizes some achievements of materials scientists in designing high entropy alloys and developing production routs for their industrial implementation, as well as highlights and discusses outstanding challenges in this way.
Abstract: The review summarizes some achievements of materials scientists in designing high entropy alloys (HEAs) and developing production routs for their industrial implementation, as well as highlights and discusses outstanding challenges in this way. Initially, the generally accepted concept of HEAs and its criticisms have been matched. Then, suggestions for their possible application have been agglomerated. After that, typical designing algorithms for metal products and structures have been considered, focusing on the rational selection of materials. Finally, correspondence of the reported data on both characteristics and properties of HEAs, as well as procedures for their heat treatment, processing and surface engineering, has been correlated with the content of recent reference books on those for conventional metals, steels and alloys. Based on the analysis of these results, some conclusions have been drawn, including generalized knowledge gaps and challenges. Also, further research directions have been proposed.
TL;DR: High-entropy materials (HEM) have played a significant role in the current research due to their novel composition with their synergistic elemental interactions resulting in enhanced functional properties as mentioned in this paper .
Abstract: High-entropy materials (HEM) have played a significant role in the current research due to their novel composition with their synergistic elemental interactions resulting in enhanced functional properties. By creating an environment for a diverse range of chemical compositions, HEMs offer unique opportunities for novel materials with superior properties compared to conventional materials. There has been a special focus on high-entropy materials, especially oxides. HEMs possess fundamentally distinct properties that have led to a wide range of applications within a variety of research fields. The current review article gives a thorough insight into the idea of High-Entropy oxide (HEO) materials along with their synthesis, properties, and functional application. A review of recent state-of-the-art publications is used exclusively to provide an overview of the current scientific breakthroughs and challenges that exist in the high entropy oxide system. This provides an overview of the subject and facilitates the design of several different high-entropy systems. The article concludes by discussing how high-entropy ceramics will be used in diverse applications in the future.
TL;DR: In this paper , an easy approach for the preparation of ZrO2-coated Y2O3 nanopowder from a solution of zirconium nitrate with commercial 2O3 powders was described.
Abstract: An easy approach is described for the preparation of ZrO2-coated Y2O3 nanopowder from a solution of zirconium nitrate with commercial Y2O3 nanopowder. The evolution process of the ZrO2 coating layer upon calcination, such as the phase and microstructure of the particles’ surface, was studied. Calcination of the powder at 700 °C resulted in ZrO2-coated Y2O3 nanopowder. The rheological properties of the suspensions of ZrO2-coated Y2O3 powders were studied. A well-dispersed suspension with a solid loading of 35.0 vol% using ZrO2-coated Y2O3 nanopowder was obtained. The consolidated green body obtained by the centrifugal casting method showed improved homogeneity with a relative density of 50.2%. Transparent ceramic with high transparency and an average grain size of 1.7 µm was obtained by presintering at 1500 °C for 16 h in air, followed by post-HIP at 1550 °C for 2 h under 200 MPa pressure. The in-line transmittance at the wavelength of 1100 nm (1.0 mm thick) reached 81.4%, close to the theoretical transmittance of Y2O3 crystal.
TL;DR: In this paper , spark plasma sintering was used for the thermoelectric composite treatment of CrMnFeCoNi/WC plasma transfer arc welding (PTA) coating to explore the difference compared with common heat treatment.
Abstract: ABSTRACT In this study, spark plasma sintering (SPS) was used for the thermoelectric composite treatment of CrMnFeCoNi/WC plasma transfer arc welding (PTA) coating to explore the difference compared with common heat treatment (HT). X-ray diffraction (XRD) was used to detect the phase composition, and a combination of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was used to characterize the microstructure. The performance of nano-indentation was tested. The results show that the coating after PTA has a large dislocation density due to internal stress, while HT and SPS treatment significantly reduce the internal stress and dislocation density of the coating. Nano-indentation test shows that the hardness of the coating after PTA is 4.24 GPa, and after HT, the hardness decreases to 4.05 GPa. However, the coating after SPS treatment has significant precipitation-strengthening effect due to the wide existence of the precipitated phase, and the hardness rises to 4.78 GPa.
TL;DR: In this paper , a systematic study of electrical resistivity, superconductive transitions and the Hall effect for three systems of compositionally complex amorphous alloys of early (TE) and late (TL) transition metals was presented.
Abstract: We present a systematic study of electrical resistivity, superconductive transitions and the Hall effect for three systems of compositionally complex amorphous alloys of early (TE) and late (TL) transition metals: (TiZrNbNi)1−xCux and (TiZrNbCu)1−xCox in a broad composition range of 0
TL;DR: A new approach for the design of alloys is presented in this paper, where high-entropy alloys with multi-principal elements were synthesized using well-developed processing technologies.
Abstract: A new approach for the design of alloys is presented in this study. These high-entropy alloys with multi-principal elements were synthesized using well-developed processing technologies. Preliminary results demonstrate examples of the alloys with simple crystal structures, nanostructures, and promising mechanical properties. This approach may be opening a new era in materials science and engineering.
01 Jul 2004-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, it was shown that the confusion principle does not apply, and other factors are more important in promoting glass formation of late transition metal rich multicomponent alloys.
Abstract: Multicomponent alloys containing several components in equal atomic proportions have been manufactured by casting and melt spinning, and their microstructures and properties have been investigated by a combination of optical microscopy, scanning electron microscopy, electron probe microanalysis, X-ray diffractrometry and microhardness measurements. Alloys containing 16 and 20 components in equal proportions are multiphase, crystalline and brittle both as-cast and after melt spinning. A five component Fe20Cr20Mn20Ni20Co20 alloy forms a single fcc solid solution which solidifies dendritically. A wide range of other six to nine component late transition metal rich multicomponent alloys exhibit the same majority fcc primary dendritic phase, which can dissolve substantial amounts of other transition metals such as Nb, Ti and V. More electronegative elements such as Cu and Ge are less stable in the fcc dendrites and are rejected into the interdendritic regions. The total number of phases is always well below the maximum equilibrium number allowed by the Gibbs phase rule, and even further below the maximum number allowed under non-equilibrium solidification conditions. Glassy structures are not formed by casting or melt spinning of late transition metal rich multicomponent alloys, indicating that the confusion principle does not apply, and other factors are more important in promoting glass formation.
TL;DR: High entropy alloys (HEAs) are barely 12 years old as discussed by the authors, and the field has stimulated new ideas and inspired the exploration of the vast composition space offered by multi-principal element alloys.
Abstract: High entropy alloys (HEAs) are barely 12 years old. The field has stimulated new ideas and has inspired the exploration of the vast composition space offered by multi-principal element alloys (MPEAs). Here we present a critical review of this field, with the intent of summarizing key findings, uncovering major trends and providing guidance for future efforts. Major themes in this assessment include definition of terms; thermodynamic analysis of complex, concentrated alloys (CCAs); taxonomy of current alloy families; microstructures; mechanical properties; potential applications; and future efforts. Based on detailed analyses, the following major results emerge. Although classical thermodynamic concepts are unchanged, trends in MPEAs can be different than in simpler alloys. Common thermodynamic perceptions can be misleading and new trends are described. From a strong focus on 3d transition metal alloys, there are now seven distinct CCA families. A new theme of designing alloy families by selecting elements to achieve a specific, intended purpose is starting to emerge. A comprehensive microstructural assessment is performed using three datasets: experimental data drawn from 408 different alloys and two computational datasets generated using the CALculated PHAse Diagram (CALPHAD) method. Each dataset emphasizes different elements and shows different microstructural trends. Trends in these three datasets are all predicted by a ‘structure in – structure out’ (SISO) analysis developed here that uses the weighted fractions of the constituent element crystal structures in each dataset. A total of 13 distinct multi-principal element single-phase fields are found in this microstructural assessment. Relationships between composition, microstructure and properties are established for 3d transition metal MPEAs, including the roles of Al, Cr and Cu. Critical evaluation shows that commercial austenitic stainless steels and nickel alloys with 3 or more principal elements are MPEAs, as well as some established functional materials. Mechanical properties of 3d transition metal CCAs are equivalent to commercial austenitic stainless steels and nickel alloys, while some refractory metal CCAs show potential to extend the service strength and/or temperature of nickel superalloys. Detailed analyses of microstructures and properties allow two major HEA hypotheses to be resolved. Although the ‘entropy effect’ is not supported by the present data, it has nevertheless made an enduring contribution by inspiring a clearer understanding of the importance of configurational entropy on phase stability. The ‘sluggish diffusion’ hypothesis is also not supported by available data, but it motivates re-evaluation of a classical concept of metallic diffusion. Building on recent published work, the CCA field has expanded to include materials with metallic, ionic or covalent bonding. It also includes microstructures with any number of phases and any type of phases. Finally, the MPEA field is shown to include both structural and functional materials applications. A significant number of future efforts are recommended, with an emphasis on developing high-throughput experiments and computations for structural materials. The review concludes with a brief description of major accomplishments of the field and insights gained from the first 12 years of research. The field has lost none of its potency and continues to pose new questions and offer new possibilities. The vast range of complex compositions and microstructures remains the most compelling motivation for future studies.
TL;DR: The concept of high entropy introduces a new path of developing advanced materials with unique properties, which cannot be achieved by the conventional micro-alloying approach based on only one dominant element as mentioned in this paper.
Abstract: This paper reviews the recent research and development of high-entropy alloys (HEAs) HEAs are loosely defined as solid solution alloys that contain more than five principal elements in equal or near equal atomic percent (at%) The concept of high entropy introduces a new path of developing advanced materials with unique properties, which cannot be achieved by the conventional micro-alloying approach based on only one dominant element Up to date, many HEAs with promising properties have been reported, eg, high wear-resistant HEAs, Co15CrFeNi15Ti and Al02Co15CrFeNi15Ti alloys; high-strength body-centered-cubic (BCC) AlCoCrFeNi HEAs at room temperature, and NbMoTaV HEA at elevated temperatures Furthermore, the general corrosion resistance of the Cu05NiAlCoCrFeSi HEA is much better than that of the conventional 304-stainless steel This paper first reviews HEA formation in relation to thermodynamics, kinetics, and processing Physical, magnetic, chemical, and mechanical properties are then discussed Great details are provided on the plastic deformation, fracture, and magnetization from the perspectives of crackling noise and Barkhausen noise measurements, and the analysis of serrations on stress–strain curves at specific strain rates or testing temperatures, as well as the serrations of the magnetization hysteresis loops The comparison between conventional and high-entropy bulk metallic glasses is analyzed from the viewpoints of eutectic composition, dense atomic packing, and entropy of mixing Glass forming ability and plastic properties of high-entropy bulk metallic glasses are also discussed Modeling techniques applicable to HEAs are introduced and discussed, such as ab initio molecular dynamics simulations and CALPHAD modeling Finally, future developments and potential new research directions for HEAs are proposed
TL;DR: This work examined a five-element high-entropy alloy, CrMnFeCoNi, which forms a single-phase face-centered cubic solid solution, and found it to have exceptional damage tolerance with tensile strengths above 1 GPa and fracture toughness values exceeding 200 MPa·m1/2.
Abstract: High-entropy alloys are equiatomic, multi-element systems that can crystallize as a single phase, despite containing multiple elements with different crystal structures. A rationale for this is that the configurational entropy contribution to the total free energy in alloys with five or more major elements may stabilize the solid-solution state relative to multiphase microstructures. We examined a five-element high-entropy alloy, CrMnFeCoNi, which forms a single-phase face-centered cubic solid solution, and found it to have exceptional damage tolerance with tensile strengths above 1 GPa and fracture toughness values exceeding 200 MPa·m(1/2). Furthermore, its mechanical properties actually improve at cryogenic temperatures; we attribute this to a transition from planar-slip dislocation activity at room temperature to deformation by mechanical nanotwinning with decreasing temperature, which results in continuous steady strain hardening.