Mechanical Alloying Of Elemental Powders Research Articles

Dissolution studies during the mechanical alloying of Inconel-718 superalloy based elemental powders

Inconel-718 superalloy with a nominal composition of Ni-19.47Fe-18Cr-0.5Al-1Ti-5 Nb-3Mo-0.02Co-0.003B was synthesized by mechanical alloying of elemental powders. Mechanical alloying was carried out in a high energy Simoloyer attritor ball mill. A sufficient quantity of powder was removed at milling intervals of 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, and 22 h for characterization by XRD, SEM, and TEM. The dissolution time of different alloying elements have been discussed in view of their atomic scattering factors and Hume-Rothery principle with the help of XRD and TEM (SAED) analysis. Complete dissolution of Fe took place at 6 h of milling, Nb at 10 h, Cr at 18 h while Mo took 22 h. A complete single-phase solid solution of γ(FCC) matrix was obtained at 22 h of milling. Crystallite size was found to decrease while the lattice parameter increased with milling time. Lattice-strain and dislocation density increased initially and later decreased due to the dynamic recrystallization process taking place within the powder particles during milling. SEM analysis indicated flattening of powder particles during the initial (0 h–4 h) stages of milling followed by heavy cold-welding at the intermediate stages (6 h–12 h). In the final stages of milling (18 h–22 h), an equilibrium between cold welding and fracturing was reached.

Mechanical and tribological characteristics of nickel-rich CoCrCuxFeNi2 high entropy-alloys

This research explores the potential to enhance the copper solubility limit in high-entropy alloys (HEAs) within the CoCrCuFeNi system by increasing the nickel content twofold and applying additional heat treatment. The CoCrCuxFeNi2 HEAs were synthesized through mechanical alloying of elemental powders followed by hot pressing. The study investigated the microstructure and phase composition of CoCrCuxFeNi2 HEAs in relation to varying copper concentrations (x = 0; 0.25; 0.5; 0.75; 1.0). The evaluation of the alloy matrix's chemical composition, which is based on the FCC solid solution, enabled the determination of copper solubility. It was found that doubling the nickel content, relative to the equiatomic ratio, facilitated the formation of HEAs with a homogenous FCC structure for copper concentrations up to x ≤ 0.75. Further heat treatment of these HEAs resulted in an enhanced copper solubility of up to 17.5 at.%. The mechanical and tribological properties of CoCrCuxFeNiy HEAs were also assessed, revealing significant improvements in tensile strength (ranging from 910 to 1045 MPa) and hardness (285–395 HV) for the CoCrCuxFeNi2 alloys. Despite the increased copper solubility limit, the heat treatment process caused a decline in mechanical properties by 35–50 %, attributed to grain size enlargement to 5.5 μm. The CoCrCu0.75FeNi2 and CoCrCuFeNi2 alloys exhibited the lowest wear rates when tested against Al2O3 counterbody, with wear rates of 1,58·10–5 and 1,48·10–5 mm3/(N·m), respectively.

Studies on alloying process of Ni-20Cr-20Fe-0.6Y2O3 powders during mechanical alloying

In the present work, Ni-20Cr-20Fe-0.6Y2O3 oxide dispersion strengthened (ODS) nickel-based alloy powders were prepared by the mechanical alloying of elemental powders in a high energy attritor mill. XRD studies indicated that a single phase solid solution was obtained at 16 h of milling. The crystallite size of the milled powder decreased significantly while lattice-strain and lattice parameter increased with milling time. After 10 h of milling, a drop in lattice strain appeared due to dynamic recrystallization. The occurrence of dynamic recrystallization has been attributed to a reduction in strain rate and crystallite size and the rise in localized high-temperature. The size of yttria (Y2O3) refined and uniformly dispersed into the gamma matrix as the milling progressed which was confirmed by TEM observations. During subsequent annealing of the 16 h milled powders a considerable grain growth occurred on a nanocrystalline scale beyond 800 °C (35.5 nm) till 1100 °C (139 nm) while nanocrystallinity (<100 nm) was retained upto 1000 °C (96.5 nm).

Manufacturing of Metal-Diamond Composites with High-Strength CoCrCuxFeNi High-Entropy Alloy Used as a Binder.

This paper focuses on the study of the structure and mechanical properties of CoCrCuxFeNi high-entropy alloys and their adhesion to single diamond crystals. CoCrCuxFeNi alloys were manufactured by the powder metallurgy route, specifically via mechanical alloying of elemental powders, followed by hot pressing. The addition of copper led to the formation of a dual-phase FCC + FCC2 structure. The CoCrCu0.5FeNi alloy exhibited the highest ultimate tensile strength (1080 MPa). Reductions in the ductility of the CoCrCuxFeNi HEAs and the tendency for brittle fracture behavior were observed at high copper concentrations. The equiatomic alloys CoCrFeNi and CoCrCuFeNi demonstrated high adhesion strength to single diamond crystals. The diamond surface at the fracture of the composites having the CoCrFeNi matrix had chromium-rich metal matrix regions, thus indicating that chromium carbide, responsible for adhesion, was formed at the composite-diamond interface. Copper-rich areas were detected on the diamond surface within the composites having the CoCrCuFeNi matrix due to the predominant precipitation of the FCC2 phase at the interfaces or the crack propagation along the FCC/FCC2 interface, resulting in the exposure of the Cu-rich FCC2 phase on the surface.

Fabrication, Microstructure, and Physico-Mechanical Properties of Fe–Cr–Ni–Mo–W High-Entropy Alloys from Elemental Powders

In this work, 35Fe30Cr20Ni10Mo5W (wt.%) and 30Fe30Cr20Ni10Mo10W (wt.%) high-entropy alloys were fabricated using a powder metallurgy route. Powder mixtures for a hot-pressure process were obtained by the mixing and mechanical alloying of elemental powders. Mechanical alloying was carried out for 1, 2.5, 5, and 10 h. X-ray phase analysis of the powder mixtures showed that with increasing time of mechanical alloying, Face-Centered Cubic (FCC), Body-Centered Cubic (BCC), and nickel–iron intermetallic phases were formed in the structure, and the volume content of molybdenum and tungsten decreased. The hot-pressing was carried out at a pressure of 30 MPa and a temperature of 1200 °C for 30 min. The maximum densities of 8.14 ± 0.02 and 8.40 ± 0.01 g/cm3 and compressive strengths of 2430 ± 30 MPa and 2460 ± 35 MPa for consolidated materials were achieved using powder mixtures after 10 h of mechanical milling, for compositions with 5 wt.% W and 10 wt.% W, respectively. The workpieces fabricated with a pressure-assisted sintering process from milled powders were found to consist of FCC, BCC, and sigma phases.

Nano oxide particles in 18Cr oxide dispersion strengthened (ODS) steels with high yttria contents

Oxide dispersion strengthened (ODS) steels containing yttria are candidate materials for fuel cladding tubes in future nuclear reactors. Their performance is determined by the size, distribution and volume fraction of the oxide dispersoids. The addition of yttria leads to a significant loss in ductility of steel limiting the yttria content in most ODS steels to 0.35%. This limitation may be overcome by powder forging of ODS steel powders. Two steels having nominal compositions (in wt%) of Fe-18Cr-2W-0.285Ti-0.5Y 2 O 3 and Fe-18Cr-2W-0.571Ti-1Y 2 O 3 were prepared by mechanical alloying of elemental powders with yttria powder in a Simoloyer attritor. The alloy powders were consolidated by powder forging at 1473 K in a flowing hydrogen atmosphere. The microstructure of powder forged ODS steels was characterized by electron microscopy. Both the steels exhibited a fine-grained recrystallized microstructure after forging. Fine (<10 nm) cuboidal oxide particles were found to be present in a ferrite matrix. A few coarse oxide particles were also observed. These coarse (>10 nm) oxide particles were present mainly along the ferrite grain boundaries. The crystal structure of oxide particles was determined by applying fast fourier transformation (FFT) on the fringes observed by high resolution transmission electron microscopy. The extracted FFTs were indexed to identify the crystal structure. The coarse particles were found to be Y 2 O 3 , TiO 2 and Cr 2 O 3 . The fine particles were identified as Y 2 TiO 5 and Y 2 Ti 2 O 7 . The face centre cubic Y 2 Ti 2 O 7 oxide particles were semi coherent whereas the orthorhombic Y 2 TiO 5 oxide particles were found to be incoherent with the ferrite matrix. The number fraction, average size and size distribution of these oxide particles was determined for both the alloys. Cr rich shells were observed around most of the particles which may prevent the coarsening of oxide particles at elevated temperatures. Reasons for this are discussed. • High yttria 18Cr ODS steels were successfully developed through novel hot powder forging route. • Recrystallized equiaxed grains with a uniform distribution of nano oxides particles were observed in the forged alloys. • A majority of oxides present were Y 2 TiO 5 or Y 2 Ti 2 O 7 oxides. Cr-rich shells were associated with these complex oxides. • The cuboidal Y 2 TiO 5 oxides were incoherent while the spherical Y 2 Ti 2 O 7 oxides were semi-coherent with the ferrite matrix. • HR-TEM also confirmed the formation of nano oxide particles such as Y 2 O 3 , TiO 2 and Cr 2 O 3 . These too were analysed.

Optimization of Ni-Co-metallic-glass powder (Ni60Cr10Ta10P16B4) (MGP) nanocomposite coatings for direct methanol fuel cell (DMFC) applications

In this research, a novel Ni-Co-metallic glass composite was fabricated and the effect of the co-deposition of Ni60Cr10Ta10P16B4 amorphous metallic glass powder (MGP) on the morphology and electrocatalytic properties of Ni–Co coatings was evaluated. The process was initiated by producing Ni60Cr10Ta10P16B4 via mechanical alloying of elemental powders using a planetary ball mill. Then, Ni–Co nanocomposite coatings were deposited on a copper substrate by the addition of different amounts of MGP via the electrodeposition method in a Watts bath. Then, the microstructure and chemical composition of the deposits were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) successively. The electrocatalytic performance of the coatings was evaluated in a methanol-containing alkaline (1 M NaOH) solution through cyclic voltammetry (CV). The enhancement of the electrocatalytic activity of Ni–Co coating through the co-deposition of MGP was observed. It was also concluded that the electrocatalytic properties of composite coatings are optimized when 7.5 g L−1 of MGP is added to the electroplating bath. Moreover, MGP was demonstrated to have altered the microstructure and the content of Co besides enhancing the roughness and specific surface of coatings.

Mechanical Alloying of Elemental Powders into Nanocrystalline (NC) Fe-Cr Alloys: Remarkable Oxidation Resistance of NC Alloys

Mechanical alloying is among the few cost effective techniques for synthesizing nanocrystalline alloy powders. This article reviews mechanical alloying or ball-milling of (NC) powders of Fe-Cr alloys of different compositions, and the remarkable oxidation resistance of the NC alloy. The article also reviews challenges in thermal processing of the mechanically alloyed powders (such as compaction into monolithic mass) and means to overcome the challenges.

Spark plasma sintering of Fe–Si–B–Cu–Nb / Finemet based alloys

The influence of mechanical alloying (MA) and spark plasma sintering (SPS) processing parameters on the microstructure, magnetic and mechanical properties of Finemet (Fe73.5Cu1Nb3Si13.5B9) type alloys was investigated. Finemet alloy powder was obtained via mechanical alloying of elemental powders for 30 h, 60 h, 90 h, and 120 h with ball to powder ratio (BPR) of 10:1 and 15:1. The milled powders were consolidated using the SPS process. The XRD patterns confirm the presence of the α-Fe3Si phase in all Finemet alloys, also broadening of the (110) peak of α-Fe3Si was observed with increasing milling time. The microhardness of Finemet alloys increases with increase in milling time primarily due to a decrease in grain size. All samples show good saturation magnetization (Ms), 120h sample exhibiting the highest Ms of 166 emu/g, however coercivity increases with increasing milling time. Additionally, α-Fe3Si crystal size decreases with increasing the BPR primarily due to higher impact energy.

Biocompatibility, corrosion, and wear resistance of β titanium alloys for biomedical applications

A novel β– Ti-xNb-3.5Sn alloys (x = 33, 36, and 39 wt. % Nb) were made using mechanical alloying of elemental powders by cold isostatic pressing. These powders were blended and then milled at different times using a planetary ball mill. The milled powders were compacted and then consolidated at different temperatures. The produced alloys were characterized as a biomedical material; using a scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) analysis, corrosion, wear resistance, as well as biocompatibility. The results showed that the titanium was completely transformed from (α to (the phase after milling time of 4 h and consolidation temperature of 1000 °C. Good results for both wear resistance, biocompatibility and corrosion resistance came from the addition of niobium. Biocompatibility slightly decreases with increasing the milling time and decreasing the consolidation temperature. This is due to the presence of FeO phase that is coming from ball contamination during the milling process. The wear resistance decreases with increasing both the milling time and consolidation temperature. The good corrosion resistance and adequate wear resistance, further that the investigated alloy is an attractive material for an orthopedic implant.

Microstructure and Mechanical Properties of Forged High Yttria 18Cr-ODS Steels

Oxide dispersion strengthened (ODS) ferritic steels are candidate materials for clad tubes in the upcoming Generation IV nuclear reactors. In the present work, a powder forging consolidation technique has been used for fabrication of ODS steels. Two alloys having nominal compositions (in weight %) of Fe-18Cr-2W-0.285Ti-0.5Y2O3 and Fe-18Cr-2W-0.571Ti-1Y2O3, respectively, have been studied in this work. The alloys were prepared by mechanical alloying of elemental powders with yttria in a Simoloyer high energy horizontal attritor. The milled powders were consolidated at 1473 K by powder forging in a flowing hydrogen gas atmosphere. Yttria to titanium ratio was kept constant at ~ 1.75 for both the alloys. TEM micrographs of the forged alloys showed fine recrystallized grains with a dispersion of nano-size Y-Ti-O oxide particles. High-resolution transmission electron microscope fringes and the corresponding fast Fourier transformation confirmed the presence of orthorhombic Y2TiO5 oxide particles in a ferrite matrix. These were the predominant oxide particles in the forged alloys. The Y2TiO5 particles were incoherent with the matrix and exhibited a cuboidal morphology. Despite their high yttria content, both the alloys showed high tensile strength and ductility at room temperature and 973 K. Reasons for this are discussed.

Deformation mechanism and enhanced properties of Cu–TiB2 composites evaluated by the in-situ tensile test and microstructure characterization

The demand for using high-performance Cu matrix composites in the electronic industry has recently increased rapidly owing to the low strength and tribological properties of pure copper. Accordingly, research and development of composite processing and related properties have increased. In this study, the Cu matrix was reinforced with different amounts of TiB2 particles by mechanical alloying of elemental powders followed by consolidation employing spark plasma sintering (SPS) whereby high relative density (∼99%) and electric conductivity (∼83–88% IACS) were obtained. Tensile properties and deformation mechanisms of the composites were studied utilizing conventional and in-situ tensile tests with simultaneous FESEM and EBSD observations. In comparison with the reference pure copper, it was found that adding 0.5 wt%TiB2 results in significant ductility increment, which was consistent with the longer strain-softening behavior observed after necking. In addition, using in-situ microstructure characterization, twinning with slip bands were confirmed as deformation mechanisms. By increasing the amount of reinforcement to 5 wt%TiB2, strengthening was remarkable while sustaining a considerable elongation. The Hall-Petch and dislocation strengthening mechanisms were the key models of strengthening based on the calculations and microstructure characterizations since by increasing the TiB2 particles, significant grain refinement and dislocation density were shown.

Synthesis of nanostructured biomaterials by high-pressure torsion: Effect of niobium content on microstructure and mechanical properties of Ti-Nb alloys

Titanium-niobium alloys with the bcc structure (β-Ti-Nb) are recently investigated for their potential use in biomedical applications; however, improvement of their mechanical properties (particularly hardness and elastic modulus) is still a challenge. In this study, nanostructured Ti-Nb alloys with different Nb contents were successfully synthesized by mechanical alloying of elemental powders via high-pressure torsion (HPT). The HPT process led to the homogenous mixture of the two elements and the formation of nanograined β phase. Examination of mechanical properties by nanoindentation and microhardness measurements revealed that all synthesized alloys exhibited high hardness and good plasticity; however, the best combination of low elastic modulus and high hardness was obtained for the sample with 25 at% Nb: E = 39 ± 11 GPa (close to the elasticity of human bone) and Hv = 3.7 ± 0.1 GPa (comparable to the hardest Ti-based biomaterials). The current results confirm the potential of HPT to synthesize nanograined Ti-Nb alloys for future biomedical applications.

Synthesis of titanium carbosilicides in Ti–Si and Ti–Si–Cu systems under mechanical alloying of elemental powders in liquid hydrocarbon

The paper studies synthesis of titanium carbosilicides in Ti–Si and Ti–Si–Cu systems under mechanical alloying of elemental powders of Ti, Si and Cu in a liquid hydrocarbon and subsequent annealing at 900 and 1300 ​°C. It has been shown that mechanical alloying of Ti–Si system facilitates the formation of Ti5Si3Cx carbosilicide as well as Ti(C,H) carbohydride which further transforms into TiC under annealing. The MAX phase Ti3SiC2 is formed in a small amount only after annealing. In addition to Ti5Si3Cx and TiC, a phase in amount of ~40 ​vol% is formed in the Ti–Si–Cu system after annealing, with the structure of Fd3¯m type and a lattice parameter of 11.12-11.13 ​Å, being an oxide or oxycarbide of the Ti–Cu–Fe system.

Spark plasma sintering of Ti-48Al intermetallic using elemental powder

Sintered compacts without further heat treatment were fabricated at 540 °C, 570 °C, 600 °C and 650 °C (below the melting temperature of aluminium) via spark plasma sintering (SPS). Ti and Al in a proportion of 52% (at.) and 48% (at.) respectively were used as the starting powders. Powder mixture without mechanical alloying was prepared in a turbula mixer for a period of 8 h. The microstructure and phases present in the elemental and mixed powders were investigated. The microstructure, phase transformation and mechanical properties of the sintered samples were investigated. The density of sintered compacts increased from 3.32 to 3.39 g/cm3 as the sintering temperature increased from 540 to 600 °C, and it shot beyond the theoretical density of 3.41 g/cm3 to a value of 3.91 g/cm3 due to loss of aluminium melt from the reaction zone during sintering. XRD analysis shows the formation of Ti, TiAl2 and Ti2Al5 as the major phases, and TiAl and Ti3Al as the minor phases. There was an indication that the powder mixture has undergone a complex reaction with the evolution of unordered (non-equilibrium) phases retained during SPS. An average microhardness value of 89.87 HV was obtained for temperature 540 to 600 °C, which increased abruptly to a value of 276.63 HV for temperature of 650 °C. This study gives insight to the discussion of the synthesis of Ti-Al intermetallic without mechanical alloying of elemental powders and no further heat treatment of consolidated powder.

Influence of process control agents on microstructure and mechanical properties of Al alloy produced by mechanical alloying

The current study aims at comparing the effect of three different process control agents (PCAs)– namely methanol (ME), ethylene glycol (EG) and stearic acid (SA)– on microstructure and mechanical properties of Al–4.4Cu–0.5Mg alloy (AA) produced by mechanical alloying of elemental powders and subsequent hot extrusion. The effect of PCAs on particle size with milling time is insignificant. The average particle size of the milled powders of all samples has reached a steady state after 3 h. Even though the grain size and its distribution in all the samples in upset-forged, hot extruded, solutionised and peak aged conditions are similar, the number density and volume fraction of nanosized θ’ precipitates are observed to be higher in the case of AA–ME sample as compared to the other samples. AA–EG samples exhibited highest hardness when compared to the other samples. This can be attributed to the higher oxygen content in AA–EG sample that results in the formation of oxides that got dispersed in the matrix. Valid tensile test data was obtained only from AA–ME sample. The failure of AA–EG and AA–SA samples can be attributed to the presence of microcracks and higher oxide content. It can be concluded that nature of PCA has significant effect on oxygen pick up, size, number density and volume fraction of precipitates and in producing defect free bulk sample.

Sintering of a nano-crystalline tungsten heavy alloy powder

A nano-crystalline Tungsten heavy alloy powder was obtained by mechanical alloying of elemental powders in a jar mill with a high ball to powder ratio. The chemical composition of the primary powder was 93 W-4.9Ni-2.1Fe (wt%). The mechanically alloyed powder had 22 nm sized tungsten crystallites distributed in an amorphous nickel base phase. Mechanical alloying reduced particle size of powders and also yielded to more uniform particles size distribution. Sintering behavior and microstructural development of that powder were studied and compared with a conventionally mixed powder. Mechanically stored energy and better distribution of primary elements in Nano-crystalline powder had decreased motivation energy of sintering and that powders showed more densification at relatively lower sintering temperatures. Sintering at low temperatures can depress grain growth during sintering and provide desirable properties. A transient intermetallic phase was formed in the nano-crystalline powder during sintering that has not been seen in conventionally mixed powders.

Comparison of Different Processing Routes for the Synthesis of Semiconducting AlSb

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.

Microstructure characterization of intermetallic (Ni-Ti)3C nanocarbide compound synthesized by mechanical alloying of elemental powders

In the present work, synthesis and microstructure characterization of nanocrystalline intermetallic carbide (Ni-Ti)3C synthesized by mechanical alloying under argon atmosphere has been investigated in detail. Microstructure characterization in terms of lattice imperfections of prepared ball-milled powders and quantitative estimation of different phases present in the powder samples have been carried out by analyzing X-ray diffraction data employing Rietveld's powder structure refinement method. Rietveld's analysis output reveals that the single phase stoichiometric nanocrystalline (Ni-Ti)3C has been formed after 7 h of ball-milling from Ni–Ti–C solid solution phase and extended milling up to 10 h confirms the phase stability of newly formed carbide phase. High resolution TEM images of 10 h ball-milled sample reveal the microstructure of prepared nano-carbide which is in good agreement as obtained from structural and microstructural evaluation by Rietveld method using XRD data. Finally, a comparative study between microstructural parameters of (Ni-Ti)3C with Ni3C helps to understand the effect of Ti doping on the phase formation of (Ni-Ti)3C.

Influence of Yttria on Oxide Dispersion Strengthened (ODS) Ferritic Steel

Oxide dispersion strengthened (ODS) ferritic steels are the most promising candidate materials for advanced fast breeder reactors of future. They exhibit excellent swelling, corrosion resistance and superior high temperature strength. Fe-18Cr-2W-0.2Ti-(0.3-0.5)Y2O3 (all in wt.%) alloys were prepared by mechanical alloying of elemental powders in Zoz Simoloyer attritor. The mechanical alloyed powders were heated in hydrogen atmosphere at 1423K in a steel can. The can was hot forged in a 100ton friction screw forging press. Increase in yttria content from 0.3 to 0.5wt.% causes a decrease in ultimate tensile strength and ductility. Reasons for this are discussed. Observed properties are related with the microstructure.