Mechanical Alloying Process Research Articles

The production of nanocrystalline AlCoCrFeNiTiZn high entropy alloy via mechanical alloying: Study of the formation mechanism, microstructural evolution, and magnetic properties of the alloy

In this paper, AlCoCrFeNiTiZn high-entropy alloy was produced in the powder and bulk form using the mechanical alloying and sintering processes. The sintering process was carried out in a tube furnace with controlled atmosphere on the cold-pressed alloyed powders which were obtained after 120 h of ball milling. The microstructures and properties of the as-milled powders and as-sintered samples were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, differential scanning calorimetry, and vibrating sample magnetometry techniques. The results revealed that both the final milled products and the as-sintered bulk HEA are composed of FCC and BCC solid solutions. The bulk alloy obtained during sintering possessed a relative density above 83% of theoretical maximum density. According to the magnetometry results, both as-milled AlCoCrFeNiTiZn powders (120 h) and as-sintered bulk HEA present good semi-hard magnetic properties and have 40.36 and 32.94 emu/g, saturation magnetization, 114.84 and 216 Oe intrinsic coercivity and 10.59 and 7.05 emu/g remanent magnetization, respectively.

A facile path from fast synthesis of Li-argyrodite conductor to dry forming ultrathin electrolyte membrane for high-energy-density all-solid-state lithium batteries

All-solid-state lithium batteries (ASSLBs), utilizing sulfide solid electrolyte, are considered as the promising design on account of their superior safety and high energy density, whereas the time-consuming preparation process of sulfide electrolyte powders and the thickness of electrolyte layer hinder their practical application. Herein, an innovative ultimate-energy mechanical alloying plus rapid thermal processing approach is employed to rapidly synthesize the crystalline Argyrodite-type conductor Li5.3PS4.3ClBr0.7 (LPSClBr) with superior ionic conductivity (11.7 mS cm−1). Furthermore, to realize the higher energy density of the battery, an ultrathin LPSClBr sulfide electrolyte membrane with superior ionic conductivity of 6.5 mS cm−1 is fabricated with the aid of polytetrafluoroethylene (PTFE) binder and the reinforced cellulose mesh. Moreover, a simple solid electrolyte interphase (SEI) is constructed on the surface of lithium metal to enhance anodic stability. Benefiting from the joint efforts of these merits, the modified ASSLBs with a high cell-level energy density of 311 Wh kg−1 show an excellent cyclic stability. The assembled all-solid-state Li2S/Li pouch cell can operate even under the severe conditions of bending and cutting, demonstrating the enormous potential of the sulfide electrolyte membrane for ASSLBs application.

Formation of columnar strengthening phases and mechanical properties of Nb–Ti–Al alloy by spark plasma sintering

In this study, Nb-27.3Ti–18Al (at.%) alloys with columnar strengthening phases were fabricated by combining spark plasma sintering (SPS) at 1250 °C and 1350 °C and mechanical alloying (MA). Two morphological powders were obtained by the MA process. Powder I was the completely alloyed powder with homogeneous Nb-based solid solution phase (Nbss), and Powder II consisted of elemental lamellae formed by cold welding. Microstructure evolution at different SPS temperatures of two kinds of powders and toughening mechanisms of alloys were analyzed, and the results have shown that Powder II could promote the formation of columnar phase besides sintering temperature. Moreover, after comparison and analysis, grain refinement of SPSed alloy with 27.3 at.% Ti content showed good fracture toughness at 1350 °C, which is better than the previously reported Nb–Ti–Al alloys by hot pressing (HP) and laser forming.

Synthesis of spherical mullite/Yb2SiO5 composite EBC powder by using mechanical alloying and spray dry processes

Abstract Environmental barrier coatings (EBCs) have been widely used as protective layers to protect the surface of ceramic components from water vapor degradation and hot corrosion at operating temperature. In this study, ytterbium monosilicate (Yb2SiO5) and mullite (3Al2O3·2SiO2) powders were synthesized by mechanical alloying to be considered as a new environmental barrier coating. The composite powder was granulated by the spray dryer process and deposited on SiC reinforced by carbon fibers (SiC/Cf) substrate using the atmospheric plasma spray method. Phases in the synthesized composite powders and the deposited EBC were identified using X-ray diffraction. A field emission scanning electron microscope equipped with energy dispersive X-ray spectroscopy was utilized to study the powder morphology and coating microstructure. After the spray dry processing, the powders exhibited a spherical morphology and good-flowability with a mean particle size of 20–40 µm. The coating thickness was measured to be between 100 and 150 μm. In addition, the results of nanoindentation testing exhibited a hardness of about 8 GPa and an elastic modulus of about 111 GPa for the deposited coatings.

Synthesis of FeCrCoNiCu high entropy alloy through mechanical alloying and spark plasma sintering processes

FeCrCoNiCu high entropy alloy (HEA) was produced through mechanical alloying (MA) and spark plasma sintering (SPS) processes. Using X-Ray diffraction, scanning electron microscopy, differential scanning calorimetry, and shear punch testing, the structural, microstructural, and mechanical properties of the milled and SPSed samples were evaluated. After 50 h of milling, a dual-phase solid solution HEA formed consisting of a major FCC phase and a minor BCC phase. Increasing milling time and repeated deformation of the powders led to increased strain and dislocation density, and eventually, an alloy with a uniform distribution of particles with reduced size was achieved. Sintering of the alloy at 750 °C resulted in the annihilation of the BCC phase and the formation of a sigma phase. Moreover, segregation of the elements due to the different mixing enthalpies led to the formation of a new FCC phase. Results revealed that the SPSed alloy that was properly sintered had a porosity of less than 8%, which resulted in good final mechanical properties such as ultimate shear strength of 300 MPa and ultimate tensile strength of 540 MPa.

Thermodynamic analysis and microstructural evolution of the W-Mo-Ni-C system produced by mechanical alloying

In this research, the microstructural evolution of the W-Mo-Ni-C system was studied by conducting a thermodynamic analysis of formation enthalpies using the Miedema model. Samples were synthetized with different milling times of up to 240 h and analyzed using X-ray diffraction to determine the phases that were produced at each stage of the synthesis. The experimental results indicated carbon diffusion into the transition metal lattice, as WC formation was observed at 120 h and NiC formation was observed at 160 h. Nanostructured MoNi3 and MoW alloys were identified at initial stages from 40 h to 120 h, and as carbon diffusion continued, the MoW alloy transformed into WMoC carbide at 200 h. The Miedema model predictions established that the necessary energy for carbide formation is much larger than that for the formation of alloys of transition metals, demonstrating that these alloys must be formed first, which was validated by experimental data. It was found that the mechanical alloying process produced materials that were out of equilibrium.

Structural study of W2B obtained via mechanical alloying of W, B4C, TiC and graphite before and after He ions irradiation

• W 6wt.%B 4 C 2wt.%TiC 1wt.%C weight ratio is used in mechanical alloying process. • Sintering at 2550 °C produces nearly single-phase W 2 B (∼98%), WB and TiC (<2%). • Irradiation with 2.5 MeV helium ions to a fluence of 5.0 × 10 20 ion/cm 2 is performed. • Irradiation has negligible effect on the W 2 B main phase content. • All trapped He atoms are found to be located in boron vacancy positions in W 2 B and WB. Elemental powders of W, B 4 C, TiC and C (graphite) in percentage weight ratio of W-–6 wt% B 4 C–2 wt% TiC–1 wt% C are used as precursors in mechanical alloying process aimed at producing tungsten-based material. The composition of the obtained material is nearly single-phase W 2 B (∼98%) with small additions of WB and TiC (<2%), unveiled by XRD analysis. Irradiation with 2.5 MeV helium ions to a fluence of 5.0 × 10 20 ion/cm 2 was performed and the induced radiation damage was assessed. The XRD data unveiled reduction in size of the grains from 300 nm to 260 nm upon the irradiation. It is observed that the irradiation had negligible effect on the W 2 B phase content, while the WB phase content increased by 0.74% and TiC phase content decreased with 0.71% upon irradiation. Raman spectral analysis showed that not only graphite’s carbon is affected by the irradiation, but also the titanium bonded carbon in TiC underwent changes, resulting in development of non-stoichiometric TiC. Positron annihilation spectroscopy is employed for investigating the presence of intrinsic defects and their evolution upon irradiation. Based on the analysis of all the obtained results, we contemplate that the detected WB phase most probably belongs to the grain boundaries of W 2 B grains. The irradiation to a fluence of 5.0 × 10 20 ion/cm 2 did not cause chemical interaction of tungsten boride phases with the carbon species of the material, which would have resulted in the appearance of new phases.

Effect of Co addition on magneto structural characteristics of Ni50−xCoxMn30Al20 Heusler alloys obtained by mechanical alloying process

Off-stoichiometric Ni50−xCoxMn30Al20 Heusler alloys were prepared by mechanical synthesis to study their structure, microstructure, morphology, chemical composition, and magnetic properties as a function of Co addition and at high temperature, using X-ray diffraction, SEM-EDS analysis, and VSM technique. At the end of the milling process, homogeneous mixtures consisting mainly of agglomerated grains of rounded shape with some debris of MICA-shaped particles were formed. All alloys have a nanocrystalline structure with an ordered Heusler B2 phase at 800 K. With increasing magnetization temperature, the crystallite size increases significantly by >100%, however, the rate of microstrain decreases drastically due to the relaxation of residual stresses. High-temperature magnetic characterizations have shown that the addition of cobalt has a direct effect on the curie temperature of the alloys as well as on their magnetic parameters Hc, Mr, and Ms. As the percentage of Co decreases, the curie temperature drops until it reaches 300 K by replacing 5% of Ni with Co. Ni45Co5Mn30Al20 has the lowest curie temperature close to 300 K and exhibits a soft magnetic behavior characterized by high saturation magnetization (Ms), and low coercivity (Hc) with an interesting coupling-magnetic exchange, which makes it a suitable candidate for soft magnetic applications.

Role of yttrium addition and annealing temperature on thermal stability and hardness of nanocrystalline CoCrFeNi high entropy alloy

CoCrFeNi high entropy alloys (HEAs) with yttrium (Y) additions (1 and 4 at. %) were nanostructured by mechanical alloying process and annealed at various temperatures between 500 °C and 1100 °C. The structure, grain growth, and hardness were studied as a function of solute addition and annealing temperature using X-ray diffraction (XRD), focused ion beam (FIB), and scanning transmission electron microscope (S/TEM) techniques, and hardness test. The thermo-physical calculations were utilized to discuss the phase evolution after mechanical alloying and annealing with respect to added solutes. The results showed that Y additions did not affect the main crystal structure of the base CoCrFeNi HEA as the solid solution with a single face-centered cubic (fcc) crystal structure was maintained even after 1 h annealing at 1100 °C. The as-milled nanocrystalline grain size of CoCrFeNi HEA yielded extensive grain growth with the temperature exposures reaching 291 nm and 1.4 μm after annealing at 900 °C and 1100 °C, respectively. However, Y additions retarded the grain growth and decreased the average grain size upon annealing as compared to the base HEA. That is, 1 and 4 at. % Y additions stabilized the grain size around 88 nm and 95 nm (both determined by TEM) after annealing at 900 °C and 1100 °C, respectively. Accordingly, the as-milled hardness of CoCrFeNi HEA dropped from 475 HV to 220 HV after annealing at 1100 °C, while the reduction in hardness was relatively gradual with Y additions and retained around 435 HV with 4 at. % Y addition even after annealing at 1100 °C. Such thermal stability may facilitate the use of HEAs at high temperatures and enable the consolidation routes of powders into dense nanocrystalline compact HEAs.

Synthesis of Fe–Al Intermetallic by Mechanical Alloying Process

Synthesis of Fe–Al Intermetallic by Mechanical Alloying Process

Microstructure development of Y–Ti–O dispersion strengthened Cu alloys fabricated by mechanical alloying

A Y–Ti–O oxide-dispersion-strengthened (ODS) Cu alloy has been successfully fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). Excessive cold-welding during high energy ball-milling was effectively suppressed by mixing TiO2 and pre-alloyed Cu(Y) powders as the raw powders. Microstructural evolutions during the MA and SPS processes and the subsequent annealing were investigated with a focus on the Y–Ti–O nano-oxides. The 12 h ball-milling failed to achieve super-saturations of Y, Ti, and O in Cu, which led to the in-situ formation of various types of oversized Y/Ti-rich oxides with very irregular morphologies during the SPS. With a prolonged ball-milling of 48 h, the subsequent SPS + annealing processes can promote a high density precipitation of ultra-fine Y–Ti–O nano-oxides. These nano-oxides were further identified as Y2Ti2O7 mostly, with a high degree of coherency in Cu. Fabricating Y–Ti–O ODS-Cu alloys via MA was thus confirmed to be technically feasible, although the dispersion of nano-oxides desires further improvement.

Mechanochemical preparation of NiCuSn nanoparticles and composites in presence of cetyltrimethylammonium bromide (CTAB) and the catalytic application of the products in homocoupling and hydration of terminal alkynes

We report the synthesis of the NiCuSn nanoparticles and nanocomposites in mechanochemical route using CTAB as milling additive. The study of grinding intensity (frequency) and time interval drew up the importance of the well-chosen operation parameters. The mild milling resulted in formation of NiSn intermetallics, while the intense ones aided the evolution of bronze and copper(I) oxide phases. The utilization of CTAB proved to be the key factor to prevent or slow down the process of mechanical alloying and to fritter the metal grains into the nanodimensions. The dynamic light scattering data demonstrated positively charged particles with average solvodynamic diameters of around 70 nm applying intense or long-term millings. Without CTAB or with relatively short or weak grindings, these values remained between 230 and 550 nm, as in the case of the surface areas getting around 20 m2/g with and 1 m2/g without CTAB. The catalytic transformation of p-methoxyphenylacetylene in dimethyl sulfoxide showed that the copper, copper(I) oxide and bronze particles managed the reaction toward the evolution of 1,3-diyne in Glaser-Hay homocoupling without base addition, while the Sn and SnO2 phases assisted to the Markovnikov-type hydration of alkyne groups. The formation of α-diketone signed that the anti-Markovnikov route was also occurred. The use of CTAB was found to exert a profound effect on the quality of catalytic end-products through the controlled generation of bronze and tin oxide phases and the solid solution of nickel atoms.

Microstructural and Mechanical Properties of AA7075 Al Alloys Produced via Mechanical Alloying Process

In this study, it is aimed to produce AA7075 materials by mechanical alloying and sintering methods. Besides, the main purpose of this study is to investigate the effect of different ball milling times on the powder and sintered samples. The milled powders and sintered samples were thoroughly investigated by different characterization techniques. Initially, AA7075 alloy powders were milled by planetary high-energy ball milling device with different milling times. While the initial particle size of commercial grade AA7075 powders were calculated 46 µm, the average particle size of the 8 hours milled powders measured as 22 μm. The effect of different milling times (i.e., 0.5, 1, 2, 4 and 8 hours) on the morphological properties of AA7075 milled powders were investigated by scanning electron microscopy (SEM) and particle size analyses. In addition, X-ray powder diffractometry (XRD) was performed to observe the differences in the crystallographic properties of the milled powders. After the powder preparation and characterization stages, in order to determine the effect of the different phases of milling process on the mechanical properties of the produced AA 7075 samples, these milled powders were consolidated via cold press followed by sintering process. According to experimental outcomes, it was observed that when the milling time reached the final stage (8 hours), the relative density of bulk AA7075 decreased by 7%, in contrast the hardness increased by 130% as compared to pure AA7075 sample fabricated by same producing history.

Preparation of nanostructural oxide dispersion strengthened (ODS) Mo alloy by mechanical alloying and spark plasma sintering, and its characterization

The nanostructural oxide dispersion strengthened (ODS) Mo alloy was successfully fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). In this study, the MA and SPS conditions were systematically studied, and the characteristics of oxide particles were investigated. The results show that the MA process can refine the powder and promote the dissolution of interstitial atoms, but introduce the ZrO2 and excess O impurities. To recycle ZrO2 impurity as a source of active element Zr for alloy preparation, the content of Zr and O with milling time was quantitatively evaluated. In the SPS process, the precipitation of oxide particles retard the densification of as-MA Mo powders. Based on the calculated linear shrinkage, the densification behavior is controlled by sintering temperature, which is driven by grain boundary or dislocation climbing. A high relative density of 99.28% in ODS Mo alloy is achieved using the optimized MA (250 rpm/18 h) and SPS (1400 °C/5 min) parameters. Additionally, the ultrafine Mo grain structure (300 nm) and uniformly dispersed nanoscale Y-Zr-O oxide particles (20.32 nm) inside grains greatly improve the mechanical properties (569.63 ± 28.08 HV0.3) of ODS Mo alloys. Non-stoichiometric Y-Zr-O particles, with different Y/Zr ratios (Y/Zr <1), possess a special fluorite crystal structure.

Mechanical alloying derived SiBCN-Ta4HfC5 composite ceramics: study on amorphous transformation mechanism

In order to study the amorphization transformation process of SiBCN-Ta4HfC5 ceramic during mechanical alloying, SiBCN-Ta4HfC5 amorphous-nanocrystalline powders were prepared and the evolution of phase, chemical valence bond and morphology of the samples during mechanical alloying were analyzed by XRD, FT-IR, Raman, XPS, SEM and TEM. In addition, the mechanism of amorphous transformation of SiBCN-Ta4HfC5 was revealed. The results show that h-BN and graphite are preferentially transformed into amorphous state, while c-Si is finally amorphized. The amorphous process of c-Si was accelerated by the introduction of nano-Ta4HfC5. The mechanical alloying process is accompanied by the formation of chemical bonds such as B-C-N, N-C and Si-C. However, Ta4HfC5 is still distributed in amorphous SiBCN in the form of nanocrystals.

Artificial Neural Network Modeling to Predict the Effect of Milling Time and TiC Content on the Crystallite Size and Lattice Strain of Al7075-TiC Composites Fabricated by Powder Metallurgy

In the study, Al7075-TiC composites were synthesized by using a novel dual step blending process followed by cold pressing and sintering. The effect of ball milling time on the microstructure of the synthesized composite powder was characterized using X-ray diffraction measurements (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). Subsequently, the integrated effects of the two-stage mechanical alloying process were investigated on the crystallite size and lattice strain. The crystallite size and lattice strain of blended samples were calculated using the Scherrer method. The prediction of the crystallite size and lattice strain of synthesized composite powders was conducted by an artificial neural network technique. The results of the mixed powder revealed that the particle size and crystallite size improved with increasing milling time. The particle size of the 3 h-milled composites was 463 nm, and it reduces to 225 nm after 7 h of milling time. The microhardness of the produced composites was significantly improved with milling time. Furthermore, an artificial neuron network (ANN) model was developed to predict the crystallite size and lattice strain of the synthesized composites. The ANN model provides an accurate model for the prediction of lattice parameters of the composites.

Properties of Fe-Si Alloy Anode for Lithium-Ion Battery Synthesized Using Mechanical Milling.

Silicon (Si)-based anode materials can increase the energy density of lithium (Li)-ion batteries owing to the high weight and volume capacity of Si. However, their electrochemical properties rapidly deteriorate due to large volume changes in the electrode resulting from repeated charging and discharging. In this study, we manufactured structurally stable Fe–Si alloy powders by performing high-energy milling for up to 24 h through the reduction of the Si phase size and the formation of the α-FeSi2 phase. The cause behind the deterioration of the electrochemical properties of the Fe–Si alloy powder produced by over-milling (milling for an increased time) was investigated. The 12 h milled Fe–Si alloy powder showed the best electrochemical properties. Through the microstructural analysis of the Fe–Si alloy powders after the evaluation of half/full coin cells, powder resistance tests, and charge/discharge cycles, it was found that this was due to the low electrical conductivity and durability of β-FeSi2. The findings provide insight into the possible improvements in battery performance through the commercialization of Fe–Si alloy powders produced by over-milling in a mechanical alloying process.

Effect of Cr2AlC particle on the dispersion strengthening of CLF-1 steel

In this study, a novel type of MAX phase carbide particle (Cr2AlC) was utilized to improve the dispersion strengthening effect on CLF-1 steel. By analyzing the mechanical alloying process of carbide dispersion strengthened steel (CDS steel) as well as the morphology change of powder particles during this whole process, the dispersion strengthening effect of Cr2AlC particle on CLF-1 steel was investigated. The results of micro hardness, tensile strength and microstructure of the sintered CDS steels demonstrated that mechanical alloying can significantly improve the tensile properties of CDS steel. The matrix without any carbide particle demonstrated higher yield strength (1078 MPa) and tensile strength (1343 MPa) than RAFM steels fabricated by means of melting, such as CLF-1, CLAM, EUROFER-97 and F82H. Similar to the oxide dispersion strengthened steel (ODS steel), four kinds of CDS steels (“base”, “+Al4C3”, “+Ti3SiC2” and “+Cr2AlC”) exhibited non-uniform grain characteristics. Cr2AlC particle exhibited the highest dispersion strengthening effect compared with Al4C3 and Ti3SiC2 due to its smaller particle size and higher density.

Synthesis and sintering of Fe-32Mn-6Si shape memory alloys prepared by mechanical alloying

Fe-32Mn-6Si alloy was produced using the mechanical alloying (MA) process of high purity powders under an inert argon gas atmosphere. The aim of this investigation is the in-depth study of the microstructure and phase transformation during the milling-sintering process of Fe-32Mn-6Si shape memory alloys. During the milling process, a significant amount of amorphous phase was created as well the crystalline martensite and austenite phases. The amorphous phase was increased by milling time enhancement and then it was decreased due to the mechano-crystalization phenomenon. It was detected that the microhardness of the alloyed powder directly depends on the amount of the amorphous phase. Furthermore, the particle size of as-milled powder firstly decreased and then increased, when the amorphous phase cojoined gradually during the milling process the transformation of martensite into austenite. The lattice strain was increased considerably during the milling process which was a reason for martensite phase creation resulting in the high shape memory properties. The amount of pre-strain for Fe-32Mn-6Si alloy was calculated to be 3.3%. Furthermore, the optimum sintering temperature was approved to be 950 °C by reduction of the percentage of pores and suitable densification.

A two-phase ultrafine-grained NbMoTaWV refractory high entropy alloy with prominent compressive properties

A NbMoTaWV high entropy alloy (HEA) was fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). Characterization of milled powders indicated that only a single body-centered cubic (BCC) solid solution phase was generated in the MA process. After SPS, a tetragonal (Ta,V)O2 oxide phase precipitated from the primary BCC phase. The NbMoTaWV alloy exhibited a compressive yielding strength (σy) of 2785 MPa, compressive strength (σmax) of 3661 MPa and strain to failure (εf) of 16.2% at room temperature. The compressive yielding strength of the sintered alloy was dramatically higher compared with most previously reported HEAs. The compressive strength of NbMoTaWV alloy at 1000 °C arrived at 1978 MPa. The excellent strength at room and elevated temperatures are mostly ascribed to the fine (Ta,V)O2 particles dispersed in the BCC matrix.