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High-entropy alloys (HEAs) with ultrafine grained and high strength can be prepared by mechanical alloying (MA) followed by sintering. Therefore, MA, as a unique solid powder processing method, has many effects on the microstructures and mechanical properties of the sintered bulk HEAs. This work focused on the alloying behavior, morphology, and phase evolution of FexCrNiAl (x = 1.0, 0.5, 0.25) HEAs by MA. The X-ray diffraction results show that the powders achieved a supersaturated solid solution body-centered-cubic (BCC) phase after MA; the crystalline size reached the nanoscale and was refined to ~80 nm. The morphology and composition of the alloyed powders were studied by scanning electron microscopy with energy dispersive spectroscopy. The results indicate that the powder was decreased to 1.59 μm for Fe1.0 powder with excellent homogeneity in composition. There exists a phase transformation during high-temperature annealing, as the non-equilibrium BCC supersaturated solid solution phase transformed into the equilibrium phase of BCC and ordered BCC (B2) phases. [ABSTRACT FROM AUTHOR]

High Entropy Alloys (HEAs) have become the most researched structural materials in the scientific community during the last decade due to their attributes like excellent strength and wear resistance. In this research, CrCuFeNiZn HEA was prepared using mechanical alloying technique. Further, X-ray diffraction (XRD) and Scanning electron microscope (SEM) analysis of prepared HEA were carried out at various milling time intervals (10 min, 5 h, 10 h, 15 h, 20 h, and 25 h) to determine solid solution formation. Results manifest that CrCuFeNiZn HEA exhibited BCC + FCC (dual phase) structure after 25 h of milling. Moreover, the crystallite size as measured from the XRD analysis for the 25 h milled powder was found to be 32.8 nm and lattice strain at the end of milling is calculated to be 0.428%. SEM-EDS analysis further confirms the homogeneous distribution of the constituting elements in the as-fabricated alloy aggregate. [ABSTRACT FROM AUTHOR]

Fe50Mn35Sn15 Heusler alloy, obtained by mechanical alloying, was subjected to larger milling times in the range of 30–50 h to study the phase stability and morphology. X-ray diffraction studies have shown that the milled samples crystallise in a disordered A2 structure. The A2 structure was found to be stable in the milling range studied, contrary to the computation studies performed on this composition. Using Rietveld refinements, the lattice parameter, mean crystallite size, and lattice strain were computed. The nature of the obtained phases by milling was found to be nanocrystalline with values below 50 nm. A linear increase rate of 0.00713 (h−1) was computed for lattice strain as the milling time increased. As the milling time increases, the lattice parameter of the cubic Heusler was found to have a decreasing behaviour, reaching 2.9517 Å at 50 h of milling. The morphological and elemental distribution—characterised by scanning electron microscopy and energy-dispersive X-ray spectroscopy—evidenced Mn and Sn phase clustering. As the milling time increased, the morphology of the sample was found to change. The Mn and Sn cluster size was quantified by elemental line profile. Electrical resistivity evolution with milling time was analysed, showing a peak for 40 h of milling time. [ABSTRACT FROM AUTHOR]

A Ni2MnSn Heusler alloy was obtained as a single B2 phase after 12 h of mechanical milling. The influence of prolonged milling on the phase stability was analysed for milling times up to 50 h, related to mean crystallite size, lattice strain, and electrical resistivity. The nature of the powders in the milled range was found to be nanocrystalline, with a mean crystallite size of about 33 ± 2 nm. An evaluation of the internal stresses induced by milling was performed, a linear behaviour was found, and a coefficient of the internal stress increase with milling time was proposed. Particle size distributions of milled samples were analysed, and the morphology of the powders was visualised by scanning electron microscopy. The elemental distribution of milled samples was quantified by energy-dispersive X-ray spectroscopy. Electrical resistivity measurements were performed on compacted samples, and their behaviour with milling time was analysed. [ABSTRACT FROM AUTHOR]

Cu-Sn alloys have been known as bronze since ancient times and widely used as electrode materials, ornaments, tableware and musical instruments. Cu-22Sn alloy fabrication by hot forging process is a Korean traditional forged high-tin bronze. The tin content is 22 percent, which is more than twice that of bronze ware traditionally used in China and the West. Copper and tin have a carbon solubility of several ppm at room temperature, making Cu-Sn-C alloys difficult to manufacture by conventional casting methods. Research on the production of carbon-added copper alloys has used a manufacturing method that is different from the conventional casting method. In this study, Cu-22Sn-xC alloy was fabricated by mechanical alloying and spark plasma sintering. The carbon solubility was confirmed in Cu-Sn alloy through mechanical alloying. The lattice parameter increased from A0 to C2, and then decreased from C4. The microstructural characteristics of sintered alloys were determined using X-ray diffraction and microscopic analysis. As a result of comparing the hardness of Cu-22Sn alloys manufactured by conventional rolling, casting, and forging and Cu-22Sn-xC alloy by sintered powder metallugy, B0 sintered alloy was the highest at about 110.9 HRB.

In this study, Al85Ni5Fe5Nd5 (at.%) alloy was produced as thin ribbons by rapid solidification method and as powders by mechanical alloying method. The structural properties of the alloys such as morphological properties, phase identification, particle size and distribution of particles were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Thermal properties of the alloy such as crystallization temperatures, activation energy and phase transformations were investigated by differential scanning calorimetry (DSC). The ribbons produced by the rapid solidification method were obtained in amorphous structure, and the powders produced by mechanical alloying were obtained in nanostructure. The XRD results showed that after 200 h of alloying process, the crystal size of the powder alloys decreased below 15 nm and nanostructured phases such as Al3Ni and Al18Nd3 were formed. The activation energy of the amorphous alloy was calculated by the Kissinger method. The activation energy for the initiation temperature of the first crystallization peak was calculated as 482 kJ/mol. This study showed that rapid solidification method is suitable for producing amorphous alloy and mechanical alloying method is suitable for producing nanocrystalline alloy. [ABSTRACT FROM AUTHOR]

In this study, a combined process of reduction and adsorption for the degradation of azo dye with nanocrystalline Fe80Si10B10 powder as a reducing agent is analyzed. A mechanical alloying technique produced the powdered alloys needed for the redox process. The synthesized nanocrystalline structure favors the efficiency of the reduction step of Reactive Black 5 (RB5) azo dye. According to the UV-Vis analysis, the reductive process alone allowed for nearly complete color removal after 3 min of reaction. In this regard, the nanocrystallized FeSiB powder has excellent application potential in the first step of the reduction processes for degrading azo dye solutions. Indeed, the nanocrystalline FeSiB powder outperforms commercial Fe powders in terms of degradation efficiency because of the formation of multiple micro-batteries between the α-Fe solid solution and the Fe3Si nanocrystalline phases, favoring the loss of electrons from iron and exhibiting different corrosion resistance. In the second step, the adsorption process, the efficient removal of intermediate undesired compounds from the reduction processes, principally aromatic amines, is analyzed. Different adsorbents, including wood, graphene oxide, activated carbon, and pine particles, were used. The results suggest that graphene oxide and activate carbon performed the best for secondary product adsorption following RB5 degradation. The current study could serve as a guide for environmental applications, such as industrial wastewater treatment, using metallic powders produced by high-energy mechanical alloying. [ABSTRACT FROM AUTHOR]

Nanocrystalline powders from the Permalloy family, Ni75Fe25, Ni79Fe16Mo5, and Ni77Fe14Cu5Mo4, were obtained by mechanical alloying starting from elemental powders. All compositions were milled for up to 24 h in a high-energy planetary ball mill. The powders were single phase and nanocrystalline as determined by X-ray diffraction studies, with larger flatted particle sizes for Ni75Fe25 (about 400 μm) and Ni77Fe14Cu5Mo4 (about 470 μm), and smaller particle sizes for Ni79Fe16Mo5 (about 170 μm). The homogeneity of the samples was verified by energy-dispersive X-ray spectroscopy (EDX). Soft magnetic composites were obtained by adding 3% of Araldite to the powders, followed by compaction at 700 MPa, and then polymerization. A very good powder covering by the polymer layer was proven by EDX elementals maps. The influence of composition change on the electrical resistivity of the compacts was studied. Hysteresis measurements in static and dynamic fields of up to 10 kHz were recorded, showing the influence of composition and particle size on the compact properties. [ABSTRACT FROM AUTHOR]

In this study, nanocrystalline Fe–Ni–Co ternary alloy powders with the composition of Fe50Ni50-xCox (x = 0–50) were prepared using a high-energy ball milling process after 30 h of milling time. Structure, microstructure, and magnetic properties were investigated in detail as a function of Co concentration using X-ray diffraction technique, scanning electron microscopy, vibrating sample magnetometer, and inductance/capacitance/resistance meter. The results indicate that BCC α-(Fe, Co) and FCC γ-(Fe, Ni) single-phase solid solutions with average crystallite sizes of 15 and 10 nm were formed successfully in Fe50Co50 and Fe50Ni50 alloys, respectively. In addition, there is a mixture of two solid solutions of FCC and BCC phases in the range of Fe–Ni–Co ternary alloy composition (i.e., 5 < × < 45). When Co concentration increases from x = 0 to x = 50, the saturation magnetization and relative permeability improve towards the Fe50Co50 alloy value, while the coercivity worsens from 12.6 to 63.4 Oe. [ABSTRACT FROM AUTHOR]

Recently, there has been an increasing demand for Co-based alloys in modern industrial applications because of their excellent magnetic properties. Therefore, given the importance of obtaining high-quality Co-based alloy, such as Co60Fe18Ti18Si4 (at%), was synthesized using the mechanical alloying (MA) process. The research concerned the microstructural, morphological, and magnetic properties evolution of Co60Fe18Ti18Si4 (at%) alloy powders synthesized by MA in a high-energy planetary ball mill under argon (Ar) atmosphere, at a speed of 300 rpm. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy, and vibrating sample magnetometer analysis were employed to characterize different alloy powdered samples as a function of MA time (10 min–50 h). The XRD result indicates that the synthesized Co-based alloy powder has a widened peak of bcc-(Co, Fe, Ti, Si) solid solution appeared after 50 h of milling time. The crystallite and the lattice strain were achieved to about 8 nm and 1.235%, respectively, after 50 h of milling time. The average particle size was obtained to about 2.727 µm after 50 h of milling time, as observed from SEM analysis. From the VSM analysis, it was observed that the synthesized alloy powders show soft ferromagnetic behaviour. After 50 h of milling time, the magnetic saturation and the coercivity were attained to about 89.68 emu/g and 155.08 Oe, respectively. [ABSTRACT FROM AUTHOR]

High-energy ball milling was used to produce two Fe-X-B (X = Nb, NiZr) nanocrystalline alloys. X-ray diffraction (XRD), differential scanning calorimetry (DSC), and vibrating sample magnetometry (VSM) were used to analyze the microstructure, thermal, and magnetic characteristics of the milled powders, the agglomerated particles (also generated during the milling process), and the compacted specimens of both alloys. The main crystallographic phase is always a bcc Fe-rich solid solution; whereas a minor Nb(B) phase is detected on powders and agglomerated particles in the Fe80Nb8B12 alloy. The crystalline size of the Fe80(NiZr)8B12 alloy is between 11 and 14 nm, whereas in the Fe80Nb8B12 alloy, it ranges between 8 and 12 nm. Microstrain and dislocation density are higher in agglomerated samples for both alloys than in milled powders. Thermal analysis detects structural relaxation and crystal growth exothermic processes with high dispersion in the temperature intervals and in the calculated apparent activation energy of the main crystallization process. Regarding magnetic behavior, the coercivity values of all powdered-agglomerated specimens were around 800 A/m. The coercivity is higher in compacted sample, but controlled annealing favors enhanced soft behavior. [ABSTRACT FROM AUTHOR]

The effect of Mg replacement with Al on the discharge capacity of Mg2Cu powder mixture was investigated. The mixture of nanocrystalline powder was prepared via mechanical alloying (MA) technique with a high energy planetary ball mill. In addition, different moles of Al (0.05, 0.1, 0.15, 0.2, and 0.3 M) were substituted to Mg2Cu powder. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to analyze changes in structure, morphology, and grain size. The obtained powder was utilized as an anode in a nickel—metal hydride battery (Ni—MH). In the specimens with 0.05 M Al content, the orthorhombic structure of Mg2Cu is emerged after 5 h milling. The results reveal that more than 0.1 M Al substitution leads to an appearance of MgCu2 peaks. Al substitution does not affect microstructure uniformity; however, it causes a decrease in crystalline size and lattice parameters. The selected area diffraction (SAD) pattern elucidates that the electrode with the Mg1.9Al0.1Cu chemical composition and 20 h milling has the maximum discharge capacity. [ABSTRACT FROM AUTHOR]

Surface modification improves the performance of materials in practical applications. In this paper, mechanical alloying pretreatment is adopted. Advanced non-equilibrium processing of a high-current pulse electron beam is then used to obtain an Sn-rich Ni-Sn alloy layer, characterized by a higher surface hardness than the initial pure nickel layer. In addition, the atomic structure of the Sn-doped nickel substrate in the alloy layer is simulated, and the improvement of the alloy layer is analyzed based on the first principle. Mechanical alloying and electron beam irradiation form fine and even nanocrystals on the surface of the nickel. Sn doping is also important for enlarging the lattice and increasing the stress. [ABSTRACT FROM AUTHOR]

High entropy alloys (HEAs) with nanocrystalline grain sizes have received significant interest in recent years; however, their microstructural integrity is compromised by a tendency for grain growth due to their high-volume fraction of grain boundaries. Here, nanocrystalline CoCrFeNi with Sm addition was synthesized through mechanical alloying, followed by annealing at temperatures up to 1100 °C and for durations of up to 24 h. The results have revealed that the 16 ± 6 nm as-milled grain size of CoCrFeNi experienced grain coarsening during the annealing process, reaching ∼1.35 ± 0.5 μm and ∼4.5 ± 1.1 μm after 1 and 24 h annealing at 1100 °C, respectively. This indicates that the nanocrystalline microstructure of CoCrFeNi lacks thermal stability at elevated temperatures. The average grain size was maintained at 110 nm after 1 h annealing at 1100 °C (T/T m = 0.74) with Sm addition. Furthermore, while large grains (∼1.5 μm) appeared after 24 h of annealing at 1100 °C, pockets of nano-sized grains were still present in the microstructure. The resistance to grain growth is ascribed to the presence of rare earth element, Sm, and the formation of Sm-based additional mixed oxide phases (Sm/Cr-O). Consequently, 517.8 ± 25 HV as-milled hardness of CoCrFeNi decreased dramatically to 221.5 ± 11 HV due to extensive grain growth but remained elevated at 442.5 ± 15 HV (84 % of as-milled hardness) with Sm addition after annealing at 1100 °C. These findings highlight the potential for optimizing the thermal and mechanical performance of CoCrFeNi HEAs in various applications. [Display omitted] • The grain size of CoCrFeNi, which was 16 ± 6 nm before milling, grew to 1.35 ± 0.5 μm after annealing at 1100 °C. • With the addition of Sm, the average grain size was maintained at 110 ± 53 nm at the same temperature. • Grain growth was retarded by Sm-based mixed oxide phases formed during the process. • The in-situ formed second phases along with the achieved smaller grain size increased the hardness. • The hardness was retained at around 442.5 ± 15 HV (84 % of as-milled hardness) after 1 h annealing at 1100 °C with Sm. [ABSTRACT FROM AUTHOR]

Multi-component nitride thin films usually show high hardness and good wear resistance due to the nanoscale structure and solid-solution strengthening effect. However, the state of N atoms in the thin film and its effects on the compressive strength is still unclear. In this work, (AlTiVCr)N multi-component nitride thin films with a face-centered cubic (FCC) structure prepared by the direct current magnetron sputtering method exhibit a superior strength of ~4.5 GPa and final fracture at a strain of ~5.0%. The excellent mechanical properties are attributed to the synergistic effects of the nanocrystalline structure, covalent bonding between N and metal atoms, and interstitial strengthening. Our results could provide an intensive understanding of the relationship between microstructure and mechanical performances for multi-component nitride thin films, which may promote their applications in micro- and nano-devices. [ABSTRACT FROM AUTHOR]

An equiatomic low-activated FeCrV ternary alloy was prepared by mechanical alloying and spark plasma sintering. The BCC solid solution alloy exhibited an excellent strength-ductility synergy properties, which was 1.85 ​GPa compressive yield strength, 3.04 ​GPa fracture strength and more than 28% plasticity at room temperature. Even at an elevated temperature of 600 ​°C, its yield strength was still more than 1 ​GPa, revealing a pronounced high temperature resistance. The FeCrV alloy had a homogeneous microstructure with high-density dislocations. A nanocrystalline characteristic was demonstrated and the average grain size was about 322 ​nm, leading to the improved mechanical properties. The strengthening mechanism was discussed in detail and the contributions of strengthening factors were calculated. The FeCrV alloy was irradiated up to 160 dpa with 2 ​MeV Au2+ ions at 573 ​K. The nanoindentation test was carried out to simply evaluate the hardening degree under such a high dose irradiation with heavy ions. The semi-quantitative analysis results show that FeCrV alloy has an excellent irradiation tolerance compared with pure Fe. [Display omitted] • Nanocrystalline multi-component FeCrV ternary alloy was fabricated by mechanical alloying and spark plasma sintering methods. • The improved mechanical properties were obtained and the excellent irradiation resistance is also demonstrated. • The outstanding mechanical performance is mainly ascribed to the dislocation and grain boundary strengthening. [ABSTRACT FROM AUTHOR]

In this work, the thermal stability of nanocrystalline (NC) AZ31/TiB2 magnesium matrix composites was investigated, while the microstructure evolution and mechanical properties were analyzed. The results indicated the AZ31/TiB2 still maintained NC structure after annealing at 350 °C for 180 min. Even at the high annealing temperature of 400 °C and 450 °C for 180 min, their average grain size just reached about 124 nm and 155 nm, indicating excellent thermal stability. The TiB2 particles with sub-micron size uniformly distributed in Mg matrix had no change in size and no reaction with matrix during the annealing treatment. Due to the strong Zener pinning effect of TiB2 particles, the grain growth of Mg matrix at high temperature was effectively inhibited. Meanwhile, the solution and precipitation behavior of Al atoms were completed in a short time, due to the existence of many grain boundaries and structural defects. By calculation, the grain growth kinetics was described by the kinetics equation D 8 - D 0 8 = k t and the activation energy Eg for grain growth was 131.6 kJ/mol, which was much higher than that of pure Mg (92 kJ/mol). Due to their excellent thermal stability, the decrease in both compressive yield strength and ultimate compressive strength was no more than 12.2% after annealing treatment. Even annealing at 450 °C for 180 min, the CYS and UCS of the samples were still above 283 MPa and 295 MPa, respectively. [ABSTRACT FROM AUTHOR]

The present research focuses on synthesizing nanocrystalline CoCrNiTiMox (x: molar ratio; x = 1, 1.5 at.%, respectively) high entropy alloy by mechanical alloying of pure metal powders for further application as feedstock in the atmospheric plasma spray process. The paper describes the phase evolution and microstructural transformation of milled powders with respect to the ball milling time and speed. A Retsch PM 100 ball mill with a ball to powder ratio of 10:1 and speeds of 200 and 300 rpm are used to synthesize the feedstock powder for plasma spraying. The ball milled powders were assessed for particle size, phase transformation and surface morphologies at regular intervals of 10, 20, 30, 40 and 50 h to optimize the ball mill process parameters. The particle morphology and chemical homogeneity studies were done by scanning electron microscope along with energy dispersive spectroscopy. The influence of Mo variation in the CoCrNiTiMox high entropy alloy in phase formation and crystal structure is studied using the x-ray diffraction technique. The results reveal that the CoCrNiTiMox high entropy alloy possesses two BCC solid solution phases and the powder milled for 10 h is selected as the feedstock powder for plasma spray due to its morphology and good homogeneity of mixing. [ABSTRACT FROM AUTHOR]

The formation of phases in the Al rich peritectic compositions of Al - Cr system was investigated under mechanical milling (MM) and subsequent annealing. MM led to the formation of nanocrystalline Al (Cr) solid solution and also caused carbon contamination originating from the organic process control agent (PCA). Al11Cr4 and AlCr2 phases were formed on annealing instead of the equilibrium peritectic compounds. Additionally, AlCr2C phase was also detected after annealing of Al-16 to 33Cr whereas Al-13Cr did not produce any intermetallic compound. The generation of the intermetallic phases was attributed to classical theories of nucleation and growth. [ABSTRACT FROM AUTHOR]

In this study, a combined process of reduction and adsorption for the degradation of azo dye with nanocrystalline Fe80Si10B10 powder as a reducing agent is analyzed. A mechanical alloying technique produced the powdered alloys needed for the redox process. The synthesized nanocrystalline structure favors the efficiency of the reduction step of Reactive Black 5 (RB5) azo dye. According to the UV-Vis analysis, the reductive process alone allowed for nearly complete color removal after 3 min of reaction. In this regard, the nanocrystallized FeSiB powder has excellent application potential in the first step of the reduction processes for degrading azo dye solutions. Indeed, the nanocrystalline FeSiB powder outperforms commercial Fe powders in terms of degradation efficiency because of the formation of multiple micro-batteries between the α-Fe solid solution and the Fe3Si nanocrystalline phases, favoring the loss of electrons from iron and exhibiting different corrosion resistance. In the second step, the adsorption process, the efficient removal of intermediate undesired compounds from the reduction processes, principally aromatic amines, is analyzed. Different adsorbents, including wood, graphene oxide, activated carbon, and pine particles, were used. The results suggest that graphene oxide and activate carbon performed the best for secondary product adsorption following RB5 degradation. The current study could serve as a guide for environmental applications, such as industrial wastewater treatment, using metallic powders produced by high-energy mechanical alloying.

Cryogenic mechanical alloying is a viable method to synthesize nanostructured alloys that exhibit improved mechanical properties without using highly contaminating, process control agents. However, cryogenically milled alloys still contain impurities introduced from the milling media and cryogenic fluid, and it is unclear how these milling parameters can be tailored to optimize alloy design. Here, milling media and cryogenic fluid were systematically varied and studied to quantify differences in impurity concentrations, microstructural evolution, and microhardness. Four derivatives of a Mo25Nb25Ta25W25 high entropy alloy were mechanically alloyed using tool steel or tungsten carbide milling media with either liquid N2 or Ar. Alloys were annealed for 100 h at 1000 °C or 1200 °C. Aberration-corrected scanning transmission electron microscopy (STEM) was primarily used to characterize as-milled and annealed specimens, and Vicker’s microindentation was used to compare hardness. Depending on the milling parameters, total impurity concentrations varied between 12 and 44 at.%, different impurity nitrides or carbides were identified in annealed specimens, and differences in hardness of up to 5 GPa were measured amongst the alloys. Overall, milling with LN2 led to the precipitation of ultrahard nitride phases that when combined with optimized heat treatments, improved the hardness beyond 17 GPa.

Nanocrystalline (NC) magnesium alloys can improve energy efficiency through enhanced mechanical properties as applying to traffic field. In this work, NC AZ91 alloys with high hardness were prepared by mechanical milling. The stability of this alloy was subsequently tested through isochronal annealing at 573 K–723 K for 1 h. The microstructural evolutions, including milled and annealed alloys, were characterized by SEM, XRD, and TEM. The activation energies at the low temperature region (573 K–673 K) and high temperature region (673 K–723 K) were 95–108 kJ/mol and 134–190 kJ/mol, respectively. After annealing at 723 K for 10 h, the average grain size increased from 91 nm to 256 nm. The results revealed that the thermal stability is superior to Mg–Al series and even Mg-RE series alloys, which could be attributed to the drag effect and thermodynamic stabilization of the grain boundaries. Nanoscale Mg 17 Al 12 precipitates with particle sizes smaller than 20 nm were observed at annealing temperatures higher than 623 K. The main contributions to the strength of annealed AZ91 alloys could be attributed to the GBs strengthening and the precipitate strengthening. The corresponding contribution ratios were 54% and 45%, respectively. • NC Mg–9Al–Zn-0.3Mn alloy presented exceptional thermal stability. • The average grain size of Mg–9Al–Zn-0.3Mn alloy increased from 91 nm to ∼256 nm after annealing at 723 K for 10 h. • After annealing at 623 K for 1 h, the hardness maintained 1.35 GPa. • Nano-scale precipitates with size of ∼20 nm had positive effect on hardening of annealed alloys. [ABSTRACT FROM AUTHOR]

The effects of the sintering holding time and cooling rate on the microstructure and mechanical properties of nanocrystalline Fe-Cr-C alloy were investigated. Nanocrystalline Fe-1.5Cr-1C (wt.%) alloy was fabricated by mechanical alloying and spark plasma sintering. Different process conditions were applied to fabricate the sintered samples. The phase fraction and grain size were measured using X-ray powder diffraction and confirmed by electron backscatter diffraction. The stability and volume fraction of the austenite phase, which could affect the mechanical properties of the Fe-based alloy, were calculated using an empirical equation. The sample names consist of a number and a letter, which correspond to the holding time and cooling method, respectively. For the 0A, 0W, 10A, and 10W samples, the volume fraction was measured at 5.56, 44.95, 6.15, and 61.44 vol.%. To evaluate the mechanical properties, the hardness of 0A, 0W, 10A, and 10W samples were measured as 44.6, 63.1, 42.5, and 53.8 HRC. These results show that there is a difference in carbon diffusion and solubility depending on the sintering holding time and cooling rate. [ABSTRACT FROM AUTHOR]

In this work, the Mg 90 Y 1.5 Ce 1.5 Ni 7 sample is successfully prepared by combining the vacuum induction melting and the mechanical milling. The phase composition and microstructure characteristics are studied by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy measurements. The hydrogenated sample is composed of MgH 2 , Mg 2 NiH 4 , CeH 2.73 phases, whereas only the MgH 2 and Mg 2 NiH 4 phases are decomposed during dehydrogenation. The hydrogen storage properties of Mg 90 Y 1.5 Ce 1.5 Ni 7 samples are measured by semi-automatic Sievert type apparatus. It is found that the samples could be fully activated within three cycles of absorption and dehydrogenation, with a reversible hydrogen storage capacity of about 5.6 wt%. Also, the "optimal hydrogenation temperature" is reduced to 200 °C, and the dehydrogenation activation energy is calculated to be 68.2 kJ/mol and 65.8 kJ/mol by using the Arrhenius and Kissinger equations, respectively. This work provides a scientific approach to promote the practical application of Mg-based alloy. • Samples were prepared by combining the induction melting and the mechanical milling. • The hydrogenated Mg 90 Y 1.5 Ce 1.5 Ni 7 sample has a nanocrystalline structure. • The "optimal hydrogenation temperature" was reduced to 200 °C through ball milling. • The dehydrogenation activation energy is evaluated to be 65.8 kJ/mol. [ABSTRACT FROM AUTHOR]

Ni3Si nanocrystalline powder was synthesized by mechanical alloying using a mixture of Ni and Si powders as raw materials. The structure and phase evolution, thermal stability and formation mechanism of Ni3Si powders during mechanical milling were investigated. The results showed that the intermediate phases Ni31Si12 and Ni74Si26 were formed firstly during high energy ball milling. After milling for 30 h, the Ni3Si nanocrystalline powder was finally attained by a series of reactions. Thermal analysis showed that the milled Ni3Si powder was stable during an annealing at 900°C for 2 h. Annealing of the milled powder leads to grain growth, decrease of microhardness, and transformation from disordered structure to ordered structure. Based on Miedema's semi-empirical theory, the thermodynamic assessment calculation of Ni–Si powder mixtures during mechanical alloying was carried out. The thermodynamic calculation results are in accordance with the experiments. [ABSTRACT FROM AUTHOR]

• Thermal stability of nanocrystalline AlxCoCrFeNi high entropy alloys is studied. • FCC in lower Al, and BCC in higher Al containing alloys are observed. • Major phases evolved in as milled condition are observed to be highly stable. • High grain growth resistance is observed upon prolonged heat treatment. Thermal stability of mechanically alloyed nanocrystalline Al x CoCrFeNi (x = 0, 0.3, 0.6, 1 mol) high entropy alloys (HEAs) has been investigated for the low and intermediate temperature range of 673–1073 K. Single phase FCC structure is observed in the as milled CoCrFeNi. A mixture of FCC and BCC phases is exhibited by × = 0.3, 0.6 and 1, alloys where the volume fraction of BCC increases with increasing Al content. Phase evolution in heat-treated Al x CoCrFeNi HEAs proceeds via increasing BCC fraction at 673 K, followed by subsequent reduction at elevated temperatures. For each alloy, the major phase observed in as milled condition and it is retained even after prolonged exposure at the 1073 K. Al favors the formation of the BCC phase due to its high affinity to form ordered B2 structures with constituent elements Co, Fe and Ni. Thermal exposure of Al x CoCrFeNi HEAs also leads to the formation of Cr 7 C 3 , owing to the higher negative free energy of carbide formation for Cr among other constituents. Transmission electron microscopy (TEM) investigations substantiated that nanostructure of milled powder is maintained even after the heat treatment. Grain growth factor for quinary HEAs is relatively lower than quaternary CoCrFeNi owing to their slower rates of diffusion. [ABSTRACT FROM AUTHOR]

CoCrFeMoTi high-entropy alloy (HEA) was synthesized using mechanical alloying and spark plasma sintering. The corresponding microstructural features and phase composition were compared with those of CoCrFeNi, CoCrFeNiTix (x = 0, 0.3 and 0.5) and CoCrFeNiMox (x = 0, 0.3, 0.5 and 0.85) HEAs. Co, Cr, Fe, Mo and Ti elemental powders were mixed in equiatomic ratio and mechanically alloyed in a planetary ball mill at 300 rpm for up to 80 h. The influence of the milling duration on the evolution of microstructure, constituent phases and morphology was studied. After 40 h of ball milling, two supersaturated BCC solid solution phases were obtained. Milling time increasing resulted in grain refinement and higher solid solution homogenization characterized by a high internal strain. A partial phase transformation from BCC to intermetallic phases when the temperature exceeds 660 °C was revealed. After SPS consolidation, the Vickers hardness was 778 ± 10 HV, in combination with an ultimate shear stress of 216 ± 20 MPa and a yield shear stress of 81 ± 15 MPa for the material sintered at 950 °C and 65 MPa. Further increasing in the sintering temperature resulted in enhanced hardness value of 1600 ± 5 but reduced yield shear stress. The failure analysis revealed a brittle fracture of the synthesized materials. [ABSTRACT FROM AUTHOR]

Nanocrystalline Mg-Zn powders have been prepared by mechanical milling using a planetary ball-mill with three ball-to-powder weight ratios of 30:1, 40:1 and 50:1 under argon atmosphere. The influence of ball-to-powder weight ratio on morphological changes, microstructural evolution and thermal behaviour of the milled powders has been examined by a combination of X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. The crystallite size and microstrain of the Mg matrix of the milled powders have been estimated using the Williamson-Hall method. The results show that in the first two hours of milling the crystallite size decreases rapidly and then slowly decrease with increasing milling time. After 18 h of milling, the crystallite size has been refined to 60-80 nm and remained unchanged. An excessively high BPR is not conducive to the deformation of the milled powders and the reduction of nanograin size. Additionally, the effectiveness of the milling process with different BPRs has also been discussed. [ABSTRACT FROM AUTHOR]

• Ni 3 Fe-5wt.%Cr soft magnetic composites was obtained by mechanical alloying and spark plasma sintering. • By milling Cr became more homogeneously distributed in the Ni 3 Fe matrix. • The electrical resistivity is increasing as the Cr is added and the mixture is milled. • The losses of Ni 3 Fe-5wt.%Cr are reduced after 60 min of milling. • Cr clusters size and distribution are responsible of the frequency behaviour of Ni-Fe-Cr nanocrystalline materials. Soft magnetic composite powders were obtained by mechanical alloying using as the main component nanocrystalline Ni 3 Fe powder, produced by mechanosynthesis, and 5 wt% of Cr powder. For the composite powder synthesis short milling times up to 60 min were used. The SMC were compacted by spark plasma sintering (SPS) method at a temperature of 700 °C. By X-ray diffraction and energy dispersive X-ray spectroscopy the incorporation and the distribution of Cr in Ni 3 Fe particles was studied. It was found that adding 5 wt% Cr to Ni 3 Fe particles increases the electrical resistivity of the samples. DC and AC magnetic characteristics have been tested and the properties of the compacts in alternative magnetic fields indicates the reduction of power losses as the milling time increases. For the composite powder obtained by 40 and 60 min milling times, a better stability of the permeability was recorded, up to a frequency of 500 Hz at an induction field of 0.05 T. [ABSTRACT FROM AUTHOR]

Abstract High entropy alloys (HEAs) have emerged as promising class of materials having equiatomic or near equiatomic multicomponent configurations. Nanostructured HEAs have added a new facet to the development of these alloys, showing remarkable strength and functional properties. The present work examined the phase evolution and thermal stability of nanocrystalline CoCrFeNi and CoCrFeMnNi HEAs prepared through mechanical alloying (MA) followed by spark plasma sintering (SPS). After MA, both the alloys showed single phase FCC structure with minor fractions of tungsten carbide arising due to contamination from milling media. After SPS, the major phase remained as FCC in both the alloys along with Cr 7 C 3 evolution. Phase stability of CoCrFeNi and CoCrFeMnNi HEAs, (MA powders and SPS pellets) were investigated in the temperature range 1073–1373 K up to 96 h. Formation of Cr 7 C 3 , concomitant with Cr-depletion in FCC matrix, was observed on heat treatment of MA powders. SPS alloys retained their mixture of FCC + Cr 7 C 3 on thermal exposure with minimal change in the fraction of carbides. The presence of single phase field in their respective phase diagrams, similar atomic sizes of constituents and non-equilibrium nature of MA combined to lend a highly stable FCC phase in the nanocrystalline HEAs studied. Graphical abstract Image 1 Highlights • Mechanically alloyed CoCrFeNi and CoCrFeMnNi HEAs form thermally stable FCC structure. • Major FCC phase, along with Cr 7 C 3, is observed after spark plasma sintering. • Atom probe tomography of CoCrFeMnNi HEA revealed Cr 7 C 3 formation during milling stage. • The mixture of FCC and Cr 7 C 3 in sintered alloys remains stable on heat treatment. [ABSTRACT FROM AUTHOR]

AlSb is a low-cost, high-band-gap semiconducting material, yet largely limited in its potential due to difficulty in the synthesis of single-phase AlSb. The present work compares different processing routes in their potency to produce bulk and nanocrystalline AlSb. Vacuum arc melting has been successfully employed, for the first time, to synthesize single-phase bulk AlSb. Owing to high vapor pressure of Sb, an optimum amount of excess Sb (3%) needs to be added to achieve single-phase line compound AlSb. Two methods, viz. mechanical alloying of elemental powders and mechanical milling of cast alloy, have been used to synthesize nanocrystalline AlSb. Nanocrystalline AlSb could be produced after ball milling the cast alloy; however, prolonged milling results in the appearance of Sb along with a non-stoichiometric Al-Sb-O oxide. Mechanical alloying of Al and Sb does not lead to appearance of single-phase AlSb, and the mixture largely consists of starting material and amorphous products. Therefore, the effectiveness of a synthesis route in producing single-phase AlSb is governed by the tendency of oxygen pickup during the processing. [ABSTRACT FROM AUTHOR]

Abstract Cu-Nb alloys with a Nb concentration range of 0 wt%∼30 wt% were prepared by mechanical alloying (MA) at room temperature. The effects of Nb content on the crystalline refinement process and mechanical properties of the immiscible Cu-Nb system were investigated by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) with energy-dispersive X-ray detection (EDX), transmission electron microscopy (TEM) and microhardness measurement. Results show that the completed dissolution of Nb in Cu can be achieved in the samples with Nb content less than ∼11 wt% after 100 h milling, although the equilibrium solubility level is nearly zero. The grain size refinement capability of MA-ed Cu-Nb powder is enhanced with increasing Nb content up to 30 wt%. This is because the susceptibility to recovery process becomes reduced, when the amount of Nb solutes segregated into the dislocation of Cu phase is increased. Cu-30wt%Nb powder milled for 100 h, the average Cu grain size is only ∼6 nm. The microhardness of the samples shows an enhancement with increasing Nb concentration. The main strengthening mechanisms of the MA-ed Cu-Nb alloys are linked to the grain size reduction and the dissolution of Nb into Cu matrix. [ABSTRACT FROM AUTHOR]

This work studies the structural evolution of TiNb x Mn alloys ( x : 0–12 wt%) synthetized by mechanical alloying in a planetary ball mill with different milling times between 1 h and 120 h. The specimens were characterized by X-ray diffraction patterns, scanning and transmission electron microscopies and Energy-dispersive X-ray spectroscopy. It was observed an evolution of the alloys developed from the raw Ti, Nb and Mn elements to bcc-TiNb x Mn alloys and, finally, novel fcc-TiNb x Mn alloys, with Fm3m space group symmetry, not previously observed. The presence of Mn promotes other interesting effects: a) the decreasing of the crystallite and the particle sizes, reaching values close to 4 nm and 400 nm, respectively, b) the partial amorphization of the fcc-TiNb x Mn alloys due to the combined effect of the Mechanical Alloying and the difference of Mn atomic size in comparison with Ti and Nb and c) the presence of Mn that decreases the Fe amount (from milling media) in the as-milled powders. [ABSTRACT FROM AUTHOR]

Nanocrystalline and nano-precipitation are two effective factors to improve comprehensive mechanical properties and irradiation tolerance. Motivated by creating the two important structural features, multi-component alloys (MCAs) FeCrVTi x (x = 0.07,0.2,0.3,0.4) and FeCrVCu y (y = 0, 0.05, 0.08, 0.2, 0.3) were designed and fabricated by mechanical alloying and spark plasma sintering. The results showed that FeCrVTi x was mainly composed of BCC matrix phase and tens of nanometers of Ti(C,N) precipitation, while BCC solid solution with nanoscale Cu precipitates was primarily present in Cu-containing MCA. Nanocrystalline is the prominent characteristic of the two MCAs, in which the average grain size is about 193 nm and 360 nm for FeCrVTi 0.2 and FeCrVCu 0.05 , respectively. The coexistence of FCC Cu precipitates with about 13 nm and ultrafine BCC Cu of only ∼3 nm was observed within the gains of FeCrVCu 0.05. The relationship between Cu nanoparticles and BCC matrix was determined. FeCrVTi 0.2 and FeCrVCu 0.05 demonstrate excellent mechanical properties with compressive yield strength of more than 1.90 Gpa, ultimate strength of above 3.0 GPa, plasticity of over 32 % and more than 590 HV microhardness at room temperature. The strengthening effects were qualitatively analyzed in detail to reveal the different influences of Ti and Cu addition on microstructure and the strengthening. • Nanocrystalline FeCrVTix and FeCrVCuy prepared by MA and SPS exhibited superior mechanical properties. • Ti(C,N) precipitates in FeCrVTix and Cu nanoparticles with FCC as well as BCC structures in FeCrVCuy were identified. • High dislocation density due to MA process leads to relatively large dislocation strengthening in both FeCrV-based MCAs. • The addition of Ti refines the grain size in FeCrVTix and results in the greater grain boundary strengthening. • The nanoscale Cu precipitation in FeCrVCuy contributes largely to the dispersion strengthening. [ABSTRACT FROM AUTHOR]

Ni 51 Mn 34 Sn 15 Heusler alloy was prepared from elemental powders in a high energy planetary ball mill under argon atmosphere for milling times up to 10 h. Alloy formation was checked by X-ray diffraction, and by the means of the Rietveld method, the amount of phases was computed. It was found that by mechanosynthesis, B 2 disordered structure was formed after 8 h of milling containing high lattice strains. By scanning electron microscopy, the morphology of the powders through the obtaining process was followed. The elemental powders degree of homogenization and distribution versus milling time was investigated by energy dispersive X-ray spectroscopy. The decrease of the magnetization with alloy formation was observed in connection with the disordered phase formation. Low and short temperature annealing was found to have an important influence on the alloy ordering to L 21 structure and to enhance magnetic properties up to a value comparable with the arc-melted sample. The Curie temperature was found to be depended on the iron contamination occurred during milling and an ordering temperature of 60 °C was measured for the phase with L 21 structure. • Ni 51 Mn 34 Sn 15 nanocrystalline Heusler alloy, with a disordered B 2 structure, was obtained after 10 h of mechanical alloying. • The low temperature annealing acts on the structure, leading to alloy ordering into L 21 structure. • The amount of ordered phase reaches 94 % for the 10 h milled and subsequently annealed sample. • The B 2 phase has low magnetisation; magnetisation increases highly for the ordered L 21 structure obtained after annealing. • The Curie temperature of the ordered L 21 structure is found to be equal with 60 °C. [ABSTRACT FROM AUTHOR]

Microcrystalline ReB 2 with a high hardness of 48 GPa measured under a small load of 0.49 N has been reported as a superhard material. Nanocrystalline ReB 2 is expected to achieve better mechanical properties than its microcrystalline counterparts. Here we report dense nanocrystalline ReB 2 bulks synthesized by modified mechanical alloying and high-pressure sintering techniques. The modified mechanical alloying technique reduces the content of WC impurity from 7.75 wt% to 1.59 wt% in as-synthesized nanocrystalline ReB 2 powders with an average grain size of 6.6 ± 2.0 nm. The extrinsic high-pressure (6 GPa) and the intrinsic nanocrystalline structure greatly promote the densification process of the ReB 2 bulks during sintering. Our optimized nanocrystalline ReB 2 bulk is ∼99% dense and with an average crystallite size of 40 nm, resulting in a high hardness of ∼33 GPa under a load of 9.8 N and indentation fracture toughness of ∼5 MPa m1/2. The high hardness can be ascribed to the synergistic effect of high density and nanocrystalline structure of ReB 2 bulks. This work provides promising strategies to largely enhance the mechanical properties of different ceramics for practical applications. • Nanocrystalline ReB 2 is prepared by mechanical alloying and high-pressure sintering. • Nanocrystalline ReB 2 is 99.3% dense and with an average grain size of ∼40 nm. • Nanocrystalline ReB 2 has high hardness of 54 GPa at a load of 0.49 N. • High density and strong grain boundary strengthening lead to high hardness. [ABSTRACT FROM AUTHOR]

In this work, a novel amorphous-nanocrystalline titanium‑niobium‑manganese solid solution ternary alloy with a Ti-33Nb-4Mn (at.%) nominal composition was developed by a High-Energy Mechanical Alloying. Nb and Mn were added to the elemental Ti as a β-phase ( bcc ) stabilizer and an amorphization promoter, respectively. The system evolved from the elemental Ti, Nb and Mn raw materials to a body centred cubic ( bcc ) TiNbMn alloy and, finally, to the formation of an original and stable face centred cubic ( fcc ) nanocrystalline TiNbMn alloy, not reported until now, at short milling time (20 h). This alloy remains invariant until 120 h. In turn, the partial amorphization of the system occurs and increases until at intermediate milling time (80 h). The production of both original fcc and the amorphous TiNbMn alloy may be beneficial for reducing the Young's modulus and improving the mechanical strength pursued for the Ti alloy. The optimal milling time respect to the amorphization, nanocrystalline size and Fe mount from milling media was 60 h and 80 h ( TiNbMn60h and TiNbMn80h ), with > 50 wt% of an amorphous phase and a crystalline domain size of approximately 5 nm. [ABSTRACT FROM AUTHOR]

In the present study, binary mixture of Mg and Cu with nominal composition of nanocrystalline Mg50Cu50 powder alloy was synthesized by mechanical alloying. The effect of mechanical alloying time on the phase evolution and microhardness of the powder alloy was investigated by X-Ray diffractometry (XRD), scanning electron microscopy (SEM) and Vickers microhardness (HV) tester. The micro hardness value of the alloy increased with increasing mechanical alloying time and it was measured ~600 Mpa for final product. The crystallite size of Mg50Cu50 alloy calculated with broadening of XRD peaks by Debye Scherrer equation. The crystallite size of the powder alloy was also confirmed by transmission electron microscopy (TEM) and it was determined approximately 10 nm. Thermal properties of the mechanically alloyed Mg50Cu50 powders were examined by differential scanning calorimetry (DSC). From DSC traces, an endothermic peak which belongs to melting point of Magnesium (Mg) element was observed at ~ 650 ˚C [ABSTRACT FROM AUTHOR]

Nanocrystalline Fe-10 wt% Si powders has been obtained by mechanical alloying. The synthesis conditions as well as their influence on the structural and magnetic properties of this soft magnetic alloy have been investigated in the light of several experimental techniques (X-ray diffraction, neutron diffraction, DSC, magnetic measurement, SEM). By X-ray diffraction (XRD) investigations have been highlighted that Fe-Si alloy is formed after 4 h of mechanical milling and the mean crystallite size is down to 14 nm (8 h milled sample). The heat treatment leads to the formation of the Fe 3 Si compound with DO3-type superstructure for low milling times. The saturation magnetisation of the as-milled powders decreases in the first 4 h of milling due to the formation of the Fe-Si alloy. The behaviour of the saturation magnetisation versus milling time and annealing was explained by the different magnetic moment of iron atoms in Fe 3 Si structure. The Curie temperature decreases from 770 °C (the Curie temperature for pure iron) to about 650 °C after 8 h of milling. [ABSTRACT FROM AUTHOR]

Artifact-free bulk nanocrystalline Cu 88 Al 11.5 Y 0.5 alloy has been synthesized by in situ consolidation of mechanically alloyed powder blend followed by annealing of the consolidated compact at 200 °C (or 0.35 T m ) for 30 min. Grain size determination and phase identification have been carried by X-ray line broadening analysis and transmission electron microscopy (TEM). Hardness measurement has demonstrated that the Hall-Petch effect is the dominant strengthening mechanism for both as-consolidated and annealed specimens. Strength improvement after short annealing time was attributed to the relaxations of non-equilibrium grain boundaries. [ABSTRACT FROM AUTHOR]

The conventional way to form a multicomponent alloy requires mixing individual elements in a single step. Phase formation, therefore, is governed by inherent thermodynamic and kinetic factors of the system. We propose here a new approach for multicomponent alloy synthesis, which involves step by step addition of constituent elements. In the present work, this is illustrated through the formation of nanocrystalline equiatomic AlCoCrFeNi by mechanical alloying. For example, first, binary CoNi is formed by milling elemental Co and Ni powders. In the subsequent steps, Fe, Cr and Al are added to form ternary (CoNiFe), quaternary (CoNiFeCr) and quinary (CoNiFeCrAl) alloy, respectively. Three different classes of binaries have been selected as initial phases, namely, B2 (AlNi, AlCo and AlFe), BCC (FeCr) and FCC (CoNi and FeNi). Remaining constituent elements are added step-wise in varying sequences and equiatomic AlCoCrFeNi is obtained in the concluding step. The final AlCoCrFeNi alloy at the end of each sequence has varied fractions of BCC and FCC phases. For instance, AlNi + Co + Fe + Cr sequence is single phase BCC, whereas the sequence FeNi + Co + Cr + Al results in a mixture of BCC (75%) and FCC (25%) phases. The extent to which a particular element stabilizes a structure (BCC/B2/FCC) has also been elucidated. [ABSTRACT FROM AUTHOR]

The thermoelectric alloy Ni51Mn19Sn30 was obtained by mechanosynthesis, from elemental powders in a planetary ball mill. The milling was carried out in the argon atmosphere for 4 h and 10 h. The structural evolution was studied by X-ray diffraction. At 4 h a mixture of phases was found. After 10 h of milling, a complete reaction leads to the formation of the Heusler Ni2MnSn alloy was observed. The morphological characterisation of the powder has been performed using scanning electron microscopy (SEM). The particle shape changes upon milling, leading to irregular shaped particles of small dimension. The particle size distribution indicates that milling leads to fragmentation of powders. [ABSTRACT FROM AUTHOR]