A short review on welding and joining of high entropy alloys

Fundacao para a Ciencia e a Tecnologia (FCT -MCTES) via the project UIDB/00667/2020 (UNIDEMI).High entropy alloys are one of the most exciting developments conceived in the materials science field in the last years. These novel advanced engineering alloys exhibit a unique set of properties, which include, among others, good mechanical performance under severe conditions in a wide temperature range and high microstructural stability over long time periods. Owing to the remarkable properties of these alloys, they can become expedite solutions for multiple structural and functional applications. Nevertheless, like any other key engineering alloy, their capacity to be welded, and thus become a permanent feature of a component or structure, is a fundamental issue that needs to be addressed to further expand these alloys’ potential applications. In fact, welding of high entropy alloys has attracted some interest recently. Therefore, it is important to compile the available knowledge on the current state of the art on this topic in order to establish a starting point for the further development of these alloys. In this article, an effort is made to acquire a comprehensive knowledge on the overall progress on welding of different high entropy alloy systems through a systematic review of both fusion-based and solid-state welding techniques. From the current literature review, it can be perceived that welding of high entropy alloys is currently gaining more interest. Several high entropy alloy systems have already been successfully welded. However, most research works focus on the well-known CoCrFeMnNi. For this specific system, both fusion and solid-state welding have been used, with no significant degradation of the joints’ mechanical properties. Among the different welding techniques already employed, laser welding is predominant, potentially due to the small size of its heat source. Overall, welding of high entropy alloys is still in its infancy, though good perspectives are foreseen for the use of welded joints based on these materials in structural applications.publishersversionpublishe

Welding of High Entropy Alloys A Review

High-entropy alloy (HEA) offers great flexibility in materials design with 3–5 principal elements and a range of unique advantages such as good microstructure stability, mechanical strength over a broad range of temperatures and corrosion resistance, etc. Welding of high entropy alloy, as a key joining method, is an important emerging area with significant potential impact to future application-oriented research and technological developments in HEAs. The selection of feasible welding processes with optimized parameters is essential to enhance the applications of HEAs. However, the structure of the welded joints varies with material systems, welding methods and parameters. A systemic understanding of the structures and properties of the weldment is directly relevant to the application of HEAs as well as managing the effect of welding on situations such as corrosion that are known to be a service life limiting factor of welded structures in conditions such as marine environments. In this paper, key recent work on welding of HEAs is reviewed in detail focusing on the research of main HEA systems when applying different welding techniques. The experimental details including sample preparation, sample size (thickness) and welding conditions reflecting energy input are summarized and key issues are highlighted. The microstructures and properties of different welding zones, in particular the fusion zone (FZ) and the heat affected zones (HAZ), formed with different welding methods are compared and presented in details and the structure-property relationships are discussed. The work shows that the weldability of HEAs varies with the HEA composition groups and the welding method employed. Arc and laser welding of AlCoCrFeNi HEAs results in lower hardness in the FZ and HAZ and reduced overall strength. Friction stir welding results in higher hardness in the FZ and achieves comparable/higher strength of the welded joints in tensile tests. The welded HEAs are capable of maintaining a reasonable proportion of the ductility. The key structure changes including element distribution, the volume fraction of face centered cubic (FCC) and body centered cubic (BCC) phase as well as reported changes in the lattice constants are summarized and analyzed. Detailed mechanisms governing the mechanical properties including the grain size-property/hardness relationship in the form of Hall–Petch (H–P) effect for both bulk and welded structure of HEAs are compared. Finally, future challenges and main areas to research are highlighted

Laser beam welding of a low density refractory high entropy alloy

In particular,the effect of different pre-heating temperatures was examined. Due to the low ductility of the material, laser beam welding at room temperature resulted in the formations of hot cracks. Sound butt joints without cracks were produced using pre-heating to T≥600 ◦C. In the initial as-cast condition, the alloy consisted of coarse bcc grains with a small amount of lens-shaped C15 Laves phase particle

Application of nano high-entropy alloys to reduce energy consumption and wear of copper oxide and high-grade iron ores in heavy mining industries— A case study

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. Problems relating to the abrasion of equipment is one of the most important issues in mining and associated industries. Hardening is a method of protecting metal equipment, metal tools, or important components against erosion, corrosion, and abrasion. This can be achieved by welding a thin layer of abrasion-resistant metal onto the surface of the work piece. The useful life of a piece of equipment or parts can be significantly increased by applying abrasion-resistant coatings, thereby reducing repair or replacement costs associated with damaged parts. This process is inexpensive in the production of parts and is often economically justifiable. This study focuses on measuring the abrasion resistance of a nano high-entropy alloy against copper oxide and high-grade iron ores. When a base alloy was coated with the nano high-entropy alloy, the abrasion indexes of iron and copper ores decreased from 0.0001647 kg to 0.0000908 kg and 0.0001472 kg to 0.0000803 kg, respectively. The standard deviation, repeatability, and reproducibility were calculated for the alloy steel blade covered with nano high entropy alloy (N-HEA), producing values of 0.00016, 0.00047, and 0.00040, respectively, while a standard alloy steel blade exhibited values of 0.0003, 0.00047, and 0.00042, respectively. High-entropy alloys and high-entropy nano-alloys have not been used as practical coatings in the mineral industry in any form to date. Utilizing high-entropy nano-alloys in this industry would introduce innovative alternatives for customers, thereby increasing competitive advantages and providing international markets and customers = with the most efficient choices of operational materials

Modification of Microstructural and Mechanical Characteristics of a AlCoCrFeNi2,1 High Entropy Alloy Euthetic Alloy, Through the Introduction of TiB2 Inoculants

High Entropy Alloys (HEAs) are nothing more than metallic compounds composed by at least five major elements, in ideally equal or similar concentrations, that can vary between 5 and 35% in atomic percentage. This new type of material has caught the interest of the scientific community be-cause of their unique set of properties, which, as it happens for the composite materials, allow them to combine certain properties that might be incompatible at first. Moreover, due to the fact of having high entropy, these materials show great thermodynamic stability at high temperatures, for longer periods of time, without occurring significant microstructural modifications that deviate these alloys from their main functionality. For this reason, the HEAs are being placed in applications with strong demands and operating conditions, such as functional and structural applications. Therefore, it is interesting to study if these already good properties can be incremented, by ad-dition of new substances, different in composition and constituent contents from the alloy, in order to further understand the influence or effect of these additions, aiming at the optimization of the prop-erties required for a specific application. In this study, the incorporation of Titanium Diboride (TiB2), through a TIG welding process, into a high entropy alloy composed of AlCoCrFeNi2,1 was tested, with the objective of verifying the influence of this compound in the weld joint, and thus in the final piece, while also analyzing its viability. Regarding the results obtained, HEA showed good weldability, with uniform beads and full pen-etration, when not inoculated. In the case of inoculation, new techniques should be further studied or existing ones optimized to obtain more uniform welds and full penetration. The inoculation with TiB2 proved to increase the overall hardness of the material, especially in the Fusion Zone, where there was total incorporation of inoculant. As for the tensile tests, the control sample showed a more brittle fracture behaviour, having therefore higher values of mechanical strength and elongation, whereas the inoculated sample be-came a little more ductile in its fracture, showing a mixed ductile and brittle fracture behaviour, with a less expressive mechanical performance.As ligas de alta entropia (LAE) são nada mais que composições metálicas constituídas por pelo menos cinco elementos principais, em quantidades idealmente iguais, ou semelhantes, podendo variar entre os 5 e os 35% em percentagem atómica. Estas ligas têm despertado um grande interesse junto da comunidade dadas os seus conjuntos de propriedades únicos, que tal como acontece um pouco com os materiais compósitos, permitem reunir determinadas propriedades que à primeira vista pode-riam ser incompatíveis. Mais, o facto de possuírem uma alta entropia, confere-lhes uma grande estabilidade a elevadas temperaturas, durante mais longos períodos de tempo, sem que com isso ocorram modificações microestruturais significantes e que desviem estes materiais da sua funcionalidade principal. Devido a este fator, estas ligas estão a ser colocadas em aplicações com fortes exigências e condições operatórias, tais como aplicações funcionais e estruturais. É, por isto, interessante estudar se é possível incrementar as que já são propriedades boas, por adição de novas substâncias inoculantes, diferentes em composição e em teores dos constituintes da liga em causa, de modo a perceber qual a influência/efeito dessas alterações, visando a otimização das propriedades requeridas para uma dada aplicação. Neste estudo foi realizada a incorporação de um inoculante, Diboreto de Titânio (TiB2), através de um processo de soldadura TIG, numa liga eutéctica de alta entropia composta por AlCoCrFeNi2,1, visando obter informações sobre a influência deste composto no cordão de soldadura e, assim, na peça final, analisando ao mesmo tempo a sua viabilidade. Relativamente aos resultados alcançados, a HEA demonstrou boa soldabilidade, com cordões uniformes e penetração total, quando não inoculada. Em caso de inoculação, há que aprofundar o estudo de novas técnicas ou otimizar as já existentes, para obter cordões mais uniformes e com pene-tração total. A inoculação com TiB2, comprovou incrementar a dureza global do material, principal-mente na Zona de Fusão, zona onde houve incorporação total de inoculante. Quanto aos testes de tração, a amostra de controlo apresentou um comportamento mais frágil de fratura, com maiores valores de resistência mecânica e elongação, ao passo que a amostra inoculada se tornou um pouco mais dúctil na sua fratura, apresentando um comportamento misto dúctil e frágil de fratura, com um desempenho mecânico menos expressiva

Re-melting behaviour and wear resistance of vanadium carbide precipitating Cr27.5Co14Fe22Mo22Ni11.65V2.85 high entropy alloy

High entropy alloys (HEAs) are among of the most promising new metal material groups. The achievable properties can exceed those of common alloys in different ways. Due to the mixture of five or more alloying elements, the variety of high entropy alloys is fairly huge. The presented work will focus on some first insights on the weldability and the wear behavior of vanadium carbide precipitation Cr27.5Co14Fe22Mo22Ni11.65V2.85 HEA. The weldability should always be addressed in an early stage of any alloy design to avoid welding-related problems afterwards. The cast Cr27.5Co14Fe22Mo22Ni11.65V2.85 HEA has been remelted using a TIG welding process and the resulting microstructure has been examined. The changes in the microstructure due to the remelting process showed little influence of the welding process and no welding-related problems like hot cracks have been observed. It will be shown that vanadium carbides or vanadium-rich phases precipitate after casting and remelting in a two phased HEA matrix. The hardness of the as cast alloy is 324HV0.2 and after remelting the hardness rises to 339HV0.2. The wear behavior can be considered as comparable to a Stellite 6 cobalt base alloy as determined in an ASTM G75 test. Overall, the basic HEA design is promising due to the precipitation of vanadium carbides and should be further investigated

Expanded microchannel heat exchanger: design, fabrication and preliminary experimental test

This paper first reviews non-traditional heat exchanger geometry, laser welding, practical issues with microchannel heat exchangers, and high effectiveness heat exchangers. Existing microchannel heat exchangers have low material costs, but high manufacturing costs. This paper presents a new expanded microchannel heat exchanger design and accompanying continuous manufacturing technique for potential low-cost production. Polymer heat exchangers have the potential for high effectiveness. The paper discusses one possible joining method - a new type of laser welding named "forward conduction welding," used to fabricate the prototype. The expanded heat exchanger has the potential to have counter-flow, cross-flow, or parallel-flow configurations, be used for all types of fluids, and be made of polymers, metals, or polymer-ceramic precursors. The cost and ineffectiveness reduction may be an order of magnitude or more, saving a large fraction of primary energy. The measured effectiveness of the prototype with 28 micron thick black low density polyethylene walls and counterflow, water-to-water heat transfer in 2 mm channels was 72%, but multiple low-cost stages could realize the potential of higher effectiveness

Wire and arc additive manufacturing of a CoCrFeMoNiV complex concentrated alloy using metal-cored wire: process, properties, and Wear Resistance

The field of complex concentrated alloys offers a very large number of variations in alloy composition. The achievable range of properties varies greatly within these variants. The experimental determination of the properties is in many cases laborious. In this work, the possibility of using metal-cored wires to produce sufficient large samples for the determination of the properties using arc-based additive manufacturing or in detail wire and arc additive manufacturing (WAAM) is to be demonstrated by giving an example. In the example, a cored wire is used for the production of a CoCrFeNiMo alloy. In addition to the process parameters used for the additive manufacturing, the mechanical properties of the alloy produced in this way are presented and related to the properties of a cast sample with a similar chemical composition. The Characterization of the resulting microstructure and wear resistance will complete this work. It will be shown that it is possible to create additively manufactured structures for a microstructure and a property determination by using metal-cored filler wires in arc-based additive manufacturing. In this case, the additively manufactured structure shows an FCC two-phased microstructure, a yield strength of 534 MPa, and a decent wear resistance

Gas tungsten arc welding of as-rolled CrMnFeCoNi high entropy alloy

Fundacao para a Ciencia e Tecnologia (FCT)- project UID/EMS/00667/2019 (UNIDEMI). FMBF acknowledges funding of CENIMAT by FEDER through the program COMPETE 2020 and National Funds through FCT-Portuguese Foundation for Science and Technology, under the project UID/CTM/50025/2019 and FCT/MCTES. This work was supported by the Future Material Discovery Project of the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT of Korea (NRF-2016M3D1A1023383). NFFA-Europe Transnational Access Activity (project reference Nf-20010136 EC and ID-806).High entropy alloys have emerged as novel engineering alloys with remarkable mechanical properties in a wide range of temperatures. Among the several high entropy alloys that were already described, the equiatomic CrMnFeCoNi alloy is the most studied one. In this work, gas tungsten arc welding of as-rolled CrMnFeCoNi high entropy alloy sheets was performed. The microstructural characterization encompassed the use of electron microscopy, including electron backscattered diffraction, synchrotron X-ray diffraction analysis, microhardness testing and mechanical evaluation. A comprehensive description of the microstructural evolution, including texture and microstrain determination, of the joint is presented and discussed. Upon mechanical testing, the joints systematically failed in the fusion zone due. The large grain size and low hardness of this region justifies the failure location. The joints' mechanical behaviour is correlated with the material microstructure.publishersversionpublishe

Laser beam welding of a CoCrFeNiMn-type high entropy alloy produced by self-propagating high-temperature synthesis

Fiber laser beam welding of a CoCrFeNiMn-type high entropy alloy (HEA) produced by self-propagating hightemperature synthesis (SHS) was reported in this work. The SHS-fabricated alloy was characterized by both ∼2 times reduced Mn content in comparison with that of the other principal components and the presence of impurities including Al, C, S, and S