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HighlightsNanocrystalline high-entropy alloy powders (HEAs) with the unprecedented combination of superior manufacturability, large aspect ratios, and thin intergranular amorphous layers are constructed via a multistage mechanical alloying strategy.FeCoNiCr0.4Cu0.2 HEAs for 20 h of dry milling and 5 h of wet milling (D20) exhibit excellent corrosion resistance, high Curie temperature, and temperature-stable broadband megahertz electromagnetic wave absorption.Developing megahertz (MHz) electromagnetic wave (EMW) absorption materials with broadband absorption, multi-temperature adaptability, and facile preparation method remains a challenge. Herein, nanocrystalline FeCoNiCr0.4Cu0.2 high-entropy alloy powders (HEAs) with both large aspect ratios and thin intergranular amorphous layers are constructed by a multistage mechanical alloying strategy, aiming to achieve excellent and temperature-stable permeability and EMW absorption. A single-phase face-centered cubic structure with good ductility and high crystallinity is obtained as wet milling precursors, via precisely controlling dry milling time. Then, HEAs are flattened to improve aspect ratios by synergistically regulating wet milling time. FeCoNiCr0.4Cu0.2 HEAs with dry milling 20 h and wet milling 5 h (D20) exhibit higher and more stable permeability because of larger aspect ratios and thinner intergranular amorphous layers. The maximum reflection loss (RL) of D20/SiO2 composites is greater than − 7 dB with 5 mm thickness, and EMW absorption bandwidth (RL < − 7 dB) can maintain between 523 and 600 MHz from − 50 to 150 °C. Furthermore, relying on the “cocktail effect” of HEAs, D20 sample also exhibits excellent corrosion resistance and high Curie temperature. This work provides a facile and tunable strategy to design MHz electromagnetic absorbers with temperature stability, broadband, and resistance to harsh environments.

Although SPS has been studied for a rapidly growing number of materials, there is limited number of researches on the fabrication and microstructural characterization of stainless steels processed by SPS. This article reviewed and provided a critical discussion on the mechanical alloying (MA) and spark plasma sintering (SPS) of dispersion-strengthened stainless steel with emphasis on process parameters, reinforcement efficiencies, microstructural evolutions, and mechanical properties. The influence of spark plasma sintering process parameters on microstructure, phase evolution, and mechanical properties of reinforced stainless steels is reviewed in this work. The role of alloying elements and ceramic reinforcements, their dispersion into the stainless steel matrix, and the importance of matrix-reinforcement interface are highlighted. Current and potential areas of applications of PM stainless steel and suggestions for future research are discussed in this paper.

Oxide-dispersion-strengthened (ODS) steel is considered as a promising candidate structural material for nuclear applications. In this study, the microstructure and mechanical properties of Y4Zr3O12-added Fe–13.5Cr–2W ODS steels, containing high contents of C and N, prepared by mechanical alloying (MA) and two-step spark plasma sintering (SPS), were investigated. The results showed that pure Y4Zr3O12 powders, with a grain size of 3.5 nm, were well prepared with NH3·H2O addition by the sol-gel method in advance, in order to avoid the formation of some coarse or undesired oxides. W was completely dissolved into the matrix after 48 h of ball milling at 300 rpm, and the main elements were uniformly distributed on the surface of the milled powders. The unexpected face-centered cubic (FCC, γ)/body-centered cubic (BCC, α) dual-phase structure of the sintered specimens, could be explained by the unexpectedly high contents of C and N from the raw powder production process, fast-sintering characteristic of SPS, and inhibitory effect of W on the diffusion of C. The experimental results were approximately consistent with the simulation results from the Thermo Calc software. The temperature combination of 800 °C and 1100 °C during the SPS process, provided a relatively more homogeneous microstructure, while the combination of 750 °C and 1150 °C, provided the highest ultimate tensile strength (UTS), of 1038 MPa, with the highest uniform elongation (UE), of 6.2%. M23C6, Cr2O3, M2(C,N), and other precipitates, were mainly distributed at grain boundaries, especially at the triple junctions, which led to Cr depletion at grain boundaries.

High-entropy alloys (HEAs) are promising structural materials due to their excellent comprehensive performances. The use of mechanically alloyed powders to deposit HEA coatings through atmospheric plasma spraying (APS) is an effective approach that can broaden the application areas of the HEAs. In this paper, a ductility–brittleness AlCoCrFeNiSi system was chosen as an object of study, and the detailed evolution of the surface morphology, particle size distribution, and microstructure of the powder during mechanical alloying was investigated. An AlCoCrFeNiSi HEA coating was deposited using powder milled for 10 h, which can be used as an ideal feedstock for APS. The surface morphology, microstructure, microhardness, and wear behavior of the coating at room temperature were investigated. The results showed that as the milling time increased, the particle size first increased, and then decreased. At the milling time of 10 h, simple body-centered cubic (BCC) and face-centered cubic (FCC) solid solution phases were formed. After spraying, the lamellar structure inside a single particle disappeared. An ordered BCC phase was detected, and the diffraction peaks of the Si element also disappeared, which indicates that phase transformation occurred during plasma spraying. A transmission electron microscopy analysis showed that nanometer crystalline grains with a grain size of about 30 nm existed in the APS coating. For the coating, an average microhardness of 612 ± 41 HV was obtained. Adhesive wear, tribo-oxidation wear, and slight abrasion wear took place during the wear test. The coating showed good wear resistance, with a volume wear rate of 0.38 ± 0.08 × 10−4 mm3·N−1·m−1, which makes it a promising coating for use in abrasive environments.

Due to the advantages such as high strength, high hardness and good wear resistance, high-entropy alloys (HEAs) attracted more and more attentions in recent decades. However, most reports on HEAs were limited to bulk materials. Although a few of studies on atmospheric plasma-sprayed (APS) HEA coatings were carried out, the wear behavior, especially the high-temperature wear behavior of those coatings has not been investigated till now. Therefore, in this study, APS was employed to deposit AlCoCrFeNiTi high-entropy alloy coating using mechanically alloyed AlCoCrFeNiTi powder as the feedstock. The phase structure of the initial powder, the feedstock powder and the as-sprayed coating was examined by an x-ray diffractometer. The surface morphology of the feedstock powder and the microstructure of the as-sprayed coating were analyzed by field emission scanning electron microscopy and energy-dispersive spectroscopy. The bonding strength and the microhardness of the as-sprayed coating were tested. The wear behavior of the coating at 25, 500, 700 and 900 °C was investigated by analysis of the wear surface morphology and measurements of the volume wear rate and the coefficient of friction.

This study presents the utilization of mill scale waste, which has attracted much attention due to its high content of magnetite (Fe3O4). This work focuses on the extraction of Fe3O4 from mill scale waste via magnetic separation, and ball milling was used to fabricate a microwave absorber. The extracted magnetic powder was ground-milled using two different techniques: (i) a conventional milling technique (CM) and (ii) mechanical alloying (MM) process. The Fe3O4/CM samples were prepared by a conventional milling process using steel pot ball milling, while the Fe3O4/MM samples were prepared using a high-energy ball milling (HEBM) method. The effect of milling time on the structural, phase composition, and electromagnetic properties were examined using X-ray diffraction (XRD) and a vector network analyzer (VNA). XRD confirmed the formation of magnetite after both the magnetic separation and milling processes. The results revealed that Fe3O4 exhibited excellent microwave absorption properties because of the synergistic characteristics of its dielectric and magnetic loss. The results showed that the Fe3O4/CM particle powder had a greater absorption power (reflection loss: <−10 dB) with 99.9% absorption, a minimum reflection loss of −30.83 dB, and an effective bandwidth of 2.30 GHz for 2 mm thick samples. The results revealed the Fe3O4/MM powders had higher absorption properties, including a higher RL of −20.59 dB and a broader bandwidth of 2.43 GHz at a matching thickness of only 1 mm. The higher microwave absorption performance was attributed to the better impedance matching property caused by the porous microstructure. Furthermore, the magnetite, Fe3O4 showed superior microwave absorption characteristics because of the lower value of permittivity, which resulted in better impedance matching. This study presents a low-cost approach method by reutilizing mill scale waste to fabricate a high purity crystalline Fe3O4 with the best potential for designing magnetic nano-sized based microwave absorbers.

Materials capable of withstanding extreme environments open promising opportunities for nuclear fusion reactors. In this study, equiatomic CrFeTaVW and CrFeTiVW high-entropy alloys are investigated as interlayer materials between W and CuCrZr. Monte Carlo and Molecular Dynamics simulations predicted a bcc-type structure for both systems. Additionally, the Monte Carlo simulation predicts lower potential energy and a more stable structure for both systems than Molecular Dynamics. For CrFeTaVW, the chemical segregation values are lower in MC than in the MD simulation, whereas for CrFeTiVW, the opposite trend is observed, with MC indicating stronger segregation values. After simulation, the high-entropy alloys were prepared by planetary ball milling, consolidated by spark plasma sintering, and analyzed using X-ray diffraction, scanning electron microscopy, and thermal diffusivity. The experimental results for the milled powders confirmed the formation of a bcc structure in both alloys. The consolidated material revealed a bcc-type structure and an Fe2Ta Laves phase for the CrFeTaVW HEA, while the CrFeTiVW HEA exhibits two different bcc-type structures. The values of CrFeTaVW and CrFeTiVW thermal diffusivity are between 3.5 and 7 mm2/s, which is consistent with the expected values for high-entropy alloys. Overall, the findings indicate that these HEAs have promising properties that can be used in extreme environments.

Cu-30 wt.% Al mixtures produced by mechanical alloying were studied using x-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The results showed that the milling time affected the morphology and particle size, and the minimum particle size was 2.91 μm for a moderate milling time of 4 h. The XRD results showed that a Cu(Al) solid solution was not detected in the Cu-rich Cu-Al mechanically-alloyed mixtures, but intermetallic compounds were formed under the conditions of this experiment. The θ-CuAl 2 phase was formed during the early milling stage (2 h), but it disappeared, and only the γ 1 -Cu 9 Al 4 phase existed as the milling time continuously increased. In addition, the effect of thermally-assisted mechanisms on the formation of intermetallic compounds could be limited by controlling the temperature of the horizontal high-energy ball milling equipment. These observations indicate that the metastable γ 1 -Cu 9 Al 4 phase can exist stably due to non-thermally activated mechanisms. Moreover, the evolution of intermetallic compounds can be explained by the following process: as the ball milling progressed, intermetallics were formed in a layered structure and were then crushed to form fine particles that adhered to the large particles that were not completely broken.

Titanium carbide (TiC) reinforced nickel (Ni) matrix composites were processed via mechanical alloying (MA) followed by spark plasma sintering (SPS) process. Mechanical alloying has gained special attention as a powerful non-equilibrium process for fabricating amorphous and nanocrystalline materials, whereas spark plasma sintering (SPS) is a unique technique for processing dense and near net shape bulk alloys with homogenous microstructure. TiC reinforcement varied from 5 to 50 wt.% into nickel matrix to investigate its effect on the microstructure and mechanical behavior of Ni-TiC composites. All Ni-TiC composites powder was mechanically alloyed using planetary high energy ball mill with 400 rpm and ball to powder ratio (BPR) 15:1 for 24 h. Bulk Ni-TiC composites were then sintered via SPS process at 50 MPa pressure and 900–1200 °C temperature. All Ni-TiC composites exhibited higher microhardness and compressive strength than pure nickel due to the presence of homogeneously distributed TiC particles within the nickel matrix, matrix grain refinement, and excellent interfacial bonding between nickel and TiC reinforcement. There is an increase in Ni-TiC composites microhardness with an increase in TiC reinforcement from 5 to 50 wt.%, and it reaches the maximum value of 900 HV for Ni-50TiC composites.

Mechanical alloying (MA) of powders represents the first processing step in the production of oxide dispersion-strengthened (ODS) alloys. MA is a time and energy-consuming process also in the production of Fe-10Al-4Cr-4Y2O3 creep and oxidation-resistant ODS nanocomposite, denoted as the FeAlOY, and it deserves to be optimized. MA is performed at two different temperatures at different times. The powder after MA, as well as the microstructure and high-temperature strength of the final FeAlOY, are characterized and the optimal MA conditions are evaluated. The obtained results show that the size distribution of the powder particles, as well as the dissolution and homogenization of the Y2O3, becomes saturated quite soon, while the homogenization of the metallic components, such as Al and Cr, takes significantly more time. The high-temperature tensile tests and grain microstructures of the secondary recrystallized FeAlOY, however, indicate that the homogenization of the metallic components during MA does not influence the quality of the FeAlOY, as the matrix of the FeAlOY is sufficiently homogenized during recrystallization. Thus, the conditions of MA correspond to sufficient dissolution and homogenization of Y2O3 and can be considered the optimal ones.