In the past 14 years, as a branch of high-entropy alloy (HEA) materials, HEA films and coatings have exhibited the attractive and unique properties, relative to the conventional film and coating ma...

https://www.tandfonline.com/doi/pdf/10.1080/21663831.2018.1434248

Microstructures and properties of high-entropy alloy films and coatings: a review

Influence of NbC particles on microstructure and mechanical properties of AlCoCrFeNi high-entropy alloy coatings prepared by laser cladding

High-entropy alloys (HEAs) are a new generation of materials that exhibit unique characteristics and properties, and are demonstrating potential in the form of thermal spray coatings for demanding environments. The use of HEAs as feedstock for coating processes has advanced due to reports of their exceptional properties in both bulk and coating forms. Emerging reports of thermal sprayed HEA coatings outperforming conventional materials have accelerated further exploration of this field. This early-stage review discusses the outcomes of combining thermal spray and HEAs. Various synthesis routes adopted for HEA feedstock preparation and their properties are discussed, with reference to the requirements of thermal spray processing. The HEA feedstock is then compared and correlated with coating microstructure and phase composition as a function of the thermal spray processing route. Subsequently, the mechanical behavior of thermal spray HEA coatings is summarized in terms of porosity, hardness, and tribological properties, along with their oxidation and electrochemical properties, followed by their potential applications. The thermal spray methods are contrasted against laser cladding and surface alloying techniques for synthesizing thick HEA coatings. Furthermore, HEAs that have displayed excellent properties via alternative processing routes, but have not been explored within the framework of thermal spray, are recommended.

/pdf/thermal-spray-high-entropy-alloy-coatings-a-review-26qv6xu62g.pdf

Thermal Spray High-Entropy Alloy Coatings: A Review

Deposition of FeCoNiCrMn high entropy alloy (HEA) coating via cold spraying

Additive manufacturing (AM) especially laser additive manufacturing (LAM), a novel manufacturing technique of layer-by-layer forming according to geometric model, provides a decent option for materials processing. It owns advantages of rapid prototyping, customization, high material utilization, and the ability to form complicated structures. This paper reviews popular LAM techniques of selective laser sintering/melting, laser metal deposition and laser direct writing. The development status of metallic materials including pure metal, steel, superalloy, titanium and aluminum alloy is presented. The challenges and application limitations of LAM are involved and the development trend in the future is forecasted. In summary, this paper gives an overview of metal LAM expecting to made helpful suggestions on future research and development.

Research status of laser additive manufacturing for metal: a review

FeCoCrNiAlBx (x = 0, 0.25, 0.50, 0.75) coatings were prepared by laser cladding to study the effects of boron on the structure and properties of high-entropy alloys coatings. The microstructure, microhardness, and wear resistance properties of the samples were investigated by scanning electron microscopy, X-ray diffraction, metallographic micro-hardness test, and friction-wear test, respectively, and the mechanism of the wear behavior was also analyzed. The results showed that the high-entropy alloys consisted of BCC phase and eutectic structure, which contained FCC phase and M2B. With boron addition, the content of BCC phase increased while that of eutectic structure decreased. The wear resistance of the high-entropy coatings was considerably improved with increasing addition of boron, and accordingly, the FeCoCrNiAlB0.75 coating showed the best wear resistance.

Tribological properties of FeCoCrNiAlBx high-entropy alloys coating prepared by laser cladding

High-entropy alloys (HEAs) are emerging as a hot research frontier in the metallic materials field. The study on the effect of alloying elements on the structure and properties of HEAs may contribute to the progress of the research and accelerate the application in actual production. FeCoCrNiAlTix (x = 0, 0.25, 0.5, 0.75, and 1 in at.%, respectively) HEA coatings with different Ti concentrations were produced on Q235 steel via laser cladding. The constituent phases, microstructure, hardness, and wear resistance of the coatings were investigated by XRD, SEM, microhardness tester and friction-wear tester, respectively. The results show that the structure of the coating is a eutectic microstructure of FCC and BCC1 at x = 0. The structure of coatings consists of both proeutectic FCC phase and the eutectic structure of BCC1 and BCC2. With the continuous addition of Ti, the amount of eutectic structure decreases. The average hardness of the FeCoCrNiAlTix HEA coatings at x = 0, 0.25, 0.5, 0.75, and 1 are 432.73 HV, 548.81 HV, 651.03 HV, 769.20 HV, and 966.29 HV, respectively. The hardness of coatings increases with the addition of Ti, where the maximum hardness is achieved for the HEA at x = 1. The wear resistance of the HEA coatings is enhanced with the addition of Ti, and the main worn mechanism is abrasive wear.

The Phase Evolution and Property of FeCoCrNiAlTix High-Entropy Alloying Coatings on Q253 via Laser Cladding

FeCoCrNiAl high entropy alloy coatings were prepared by supersonic air-plasma spraying. The coatings were post-treated by vacuum heat treatment at 600 and 900 °C, and laser re-melting with 300 W, respectively, to study the influence of different treatments on the structure and properties of the coatings. The phase constitution, microstructure and microhardness of the coatings after treatments were investigated using X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry. Results showed that the as-sprayed coatings consisted of pure metal and Fe-Cr. The AlNi3 phase was obtained after the vacuum heat treatment process. A body-centered cubic structure with less AlNi3 could be found in the coating after the laser re-melting process. The average hardness values of the as-sprayed coating and the coatings with two different temperature vacuum heat treatments and with laser re-melting were 177, 227, 266 and 682 HV, respectively. This suggests that the vacuum heat treatment promoted the alloying process of the coatings, and contributed to the enhancement of the coating wear resistance. The laser re-melted coating showed the best wear resistance.

Influence of laser re-melting and vacuum heat treatment on plasma-sprayed FeCoCrNiAl alloy coatings

FeCoCrNiAlNb x
 (x = 0, 0.25, 0.5, 0.75, and 1) high-entropy alloy (HEA) coatings were prepared by laser cladding to explore the effects of the addition of Nb on the microstructure and wear resistance properties of FeCoCrNiAlNb x
 HEAs. These effects were analyzed by microstructure and wear performance tests. The experimental results show that the structure of FeCoCrNiAlNb x
 consists of BCC and FCC phases at x = 0, 0.25, and 0.5. FCC2 formed at x = 0.75, and Fe2Nb was detected at x = 1. The content of FCC phase increased with the increasing content of Nb. At x = 0, 0.25, 0.5, 0.75, and 1, the average hardness values were 439, 685, 773, 672, and 561 HV, whereas the mass losses were 3.4, 1.9, 1.6, 2.3, and 2.5 mg after a sliding wear test against a WC ball, respectively. The hardness and wear resistance clearly increased initially and then decreased with the continuous addition of Nb. The wear resistance is highest for the alloy with x = 0.5. Thus, the effect of the addition of Nb should be considered and rationally determined before the preparation of FeCoCrNiAlNb x
 HEA to improve the wear resistance.

Structural Evolution and Performance Changes in FeCoCrNiAlNb x High-Entropy Alloy Coatings Cladded by Laser

The invention provides high-entropy alloy powder and a preparation method of a high-hardness high-entropy alloy coating. An element B is added in a conventional FeNiAlCrCo alloy, the diameters of crystalline grains of the high-entropy alloy coating prepared from the high-entropy alloy powder are greatly reduced, so that the high-entropy alloy coating has quite high hardness, and after the addition amount of the element B is further analyzed, the optimal addition amount of the element B is obtained.

High-entropy alloy powder and preparation method of high-hardness high-entropy alloy coating

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