High Energy Attrition Milling Research Articles

Selective laser melted CrMnFeCoNi + 3 wt% Y2O3 high-entropy alloy matrix nanocomposite: Fabrication, microstructure and nanoindentation properties

A Y2O3-reinforced equiatomic CrMnFeCoNi high-entropy alloy (HEA) matrix nanocomposite was fabricated by high-energy attrition milling and selective laser melting (SLM) additive manufacturing. The SLM-built HEA nanocomposite possessed heterogeneous grain structures and substructures decorated with a dislocation network and exhibited a high number density of nano-sized Y2O3. The SLM-built HEA + Y2O3 nanocomposite exhibited higher nanohardness (~9.22 GPa) than other equiatomic CrMnFeCoNi HEAs produced by casting (~4.13 GPa) and SLM (~6.95 GPa). This suggested that the dispersion hardening by the Y2O3 nanoparticles enabled superior mechanical properties. This study, therefore, demonstrated that Y2O3 reinforcement can effectively improve the mechanical properties of SLM-built CrMnFeCoNi HEA matrix nanocomposites.

Effect of high-energy attrition milling and La2O3 content on the microstructure of Mo-La2O3 composite powders

Mo-La2O3 composites are potential high-temperature materials for future technology devices operating at temperatures above 1300 °C because of their excellent thermal stability, high mechanical properties and good creep resistance. In this study, we focused on the preparation of Mo-matrix/lanthanum oxide (La2O3) composite powders using high-energy attrition milling. The effects of rotational milling speed (350 and 800 rpm) and La2O3 content (2.5 and 10 vol. %) on the microstructural evolution, phase composition, morphology, and distribution of the second phase in the produced composite Mo-La2O3 powders were investigated in details. The results show that the most interesting composite powder was Mo-10 vol.% La2O3 produced using a rotational speed of 800 rpm, which exhibited better distribution, smaller particle size and higher amount of ceramic phase introduced in the interiors of the Mo grains.

Biodegradable nanocomposite Fe–Ag load-bearing scaffolds for bone healing

Processing and properties of biodegradable load-bearing nanocomposite Fe–Ag scaffolds for bone ingrowth are reported. Fe–Ag nanocomposites were prepared employing high energy attrition milling of powders. Scaffolds with regular interconnected 300–400 μm pores and 60–75% porosity were prepared by cold sintering/high pressure consolidation of nanocomposite Fe–Ag granules, blended with porogen – highly water soluble sugar particles. The scaffolds' strength and permeability were found to be inversely related and to be strongly dependent on porosity. Presence of galvanic nanocouples in Fe5Ag and Fe10Ag resulted in desirable increase of degradation rate in saline solution as compared to pure Fe. The 70% and 75% macroporous Fe–Ag scaffolds possess high compressive strength (9.1–14.9 MPa) and permeability (1.0–3.5·10−10 m2) being in the range of trabecular/spongy bone. Method of estimation surface area of metal based macroporous scaffolds was proposed and successfully used.

Cold sintering of Fe-Ag and Fe-Cu by consolidation in high pressure gradient

The paper states the results of obtaining Fe—Ag and Fe—Cu dense nanocomposites from composite powders consolidated by cold sintering in the high pressure gradient, as well as from nanosize powders of silver (Ag), iron (Fe) and copper (Cu). The results of mechanical tests conducted on Fe—Ag and Fe—Cu nanocomposites are provided. Nanocomposite powders were obtained by high energy attrition milling of carbonyl iron (Fe) micron scale powder and nanosize silver oxide powder (Ag2O), as well as iron and cuprous oxide (Cu2O) nanopowders. High resolution scanning electron microscopy was used to study the microstructure. Compacts featuring approximately 70 % of full density were annealed in hydrogen atmosphere to reduce silver and cuprous oxides to metals and to remove oxide layers from the surface of iron powder particles. This was followed by cold sintering — consolidation under high pressure at a room temperature. The data on specimen density dependence on pressure in the range of 0,25 —3,0 GPa were obtained. Densities were above 95 % of the full density for all nanocomposites, and close to 100 % of the full density under 3,0 GPa for Ag and Cu powders. High mechanical properties in three-point bending and compression were observed for all nanocomposites. It was found that mechanical properties of nanocomposites are substantially higher as compared with composites obtained from micron scale powders. Higher ductility was observed in Fe—Ag and Fe—Cu nanocomposites as compared with specimens obtained from nanostructured Fe.

Mechanical, degradation and drug-release behavior of nano-grained Fe-Ag composites for biomedical applications.

An original fabrication route of high-strength bulk Fe-5Ag and Fe-10Ag nanocomposites with enhanced degradation rate is reported. Near fully dense materials with fine nanostructures and uniform distribution of Ag nanoparticles were obtained employing high energy attrition milling of Fe-Ag2O powder blends followed by cold sintering - high pressure consolidation at ambient temperature that allowed the retention of the nanoscale structure. Annealing in hydrogen flow at 550 °C resulted in enhanced ductility without coarsening the nanostructure. The strength in compression of Fe5Ag and Fe10Ag nanocomposites was several-fold higher than the values reported for similar composites with micrometer grain size. The galvanic action of finely dispersed Ag nanoparticles greatly increased the corrosion rate and degradation kinetics of iron. Following four weeks immersion of Fe-Ag nanocomposites in saline solution, a more than 10% weight loss accompanied by less than 25% decrease in bending strength were measured. The interconnected nanoporosity of cold sintered Fe-Ag nanocomposites was utilized for incorporation of vancomycin that was gradually released upon immersion. In cell culture experiments, the Fe-Ag nanocomposites supported the attachment of osteoblast cells and exhibited no signs of cytotoxicity. The results suggest that the proposed Fe-Ag nanocomposites could be developed into attractive biodegradable load-bearing implant materials with drug delivery capability.

Bioresorbable β-TCP-FeAg nanocomposites for load bearing bone implants: High pressure processing, properties and cell compatibility

In this paper, the processing and properties of iron-toughened bioresorbable β-tricalcium phosphate (β-TCP) nanocomposites are reported. β-TCP is chemically similar to bone mineral and thus a good candidate material for bioresorbable bone healing devices; however intrinsic brittleness and low bending strength make it unsuitable for use in load-bearing sites. Near fully dense β-TCP-matrix nanocomposites containing 30vol% Fe, with and without addition of silver, were produced employing high energy attrition milling of powders followed by high pressure consolidation/cold sintering at 2.5GPa. In order to increase pure iron's corrosion rate, 10 to 30vol% silver were added to the metal phase. The degradation behavior of the developed composite materials was studied by immersion in Ringer's and saline solutions for up to 1month. The mechanical properties, before and after immersion, were tested in compression and bending. All the compositions exhibited high mechanical strength, the strength in bending being several fold higher than that of polymer toughened β-TCP-30PLA nanocomposites prepared by the similar procedure of attrition milling and cold sintering, and of pure high-temperature sintered β-TCP. Partial substitution of iron with silver led to an increase in both strength and ductility. Furthermore, the galvanic action of silver particles dispersed in the iron phase significantly accelerated in vitro degradation of β-TCP-30(Fe-Ag) nanocomposites. After 1month immersion, the composites retained about 50% of their initial bending strength. In cell culture experiments, β-TCP-27Fe3Ag nanocomposites exhibited no signs of cytotoxicity towards human osteoblasts suggesting that they can be used as an implant material.

Microstructure, mechanical characteristics and cell compatibility of β-tricalcium phosphate reinforced with biodegradable Fe–Mg metal phase

The use of beta-tricalcium phosphate (β-TCP) ceramic as a bioresorbable bone substitute is limited to non-load-bearing sites by the material׳s brittleness and low bending strength. In the present work, new biocompatible β-TCP-based composites with improved mechanical properties were developed via reinforcing the ceramic matrix with 30vol% of a biodegradable iron–magnesium metallic phase. β-TCP-15Fe15Mg and β-TCP-24Fe6Mg (vol%) composites were fabricated using a combination of high energy attrition milling, cold sintering/high pressure consolidation of powders at room temperature and annealing at 400°C. The materials synthesized had a hierarchical nanocomposite structure with a nanocrystalline β-TCP matrix toughened by a finely dispersed nanoscale metallic phase (largely Mg) alongside micron-scale metallic reinforcements (largely Fe). Both compositions exhibited high strength characteristics; in bending, they were about 3-fold stronger than β-TCP reinforced with 30vol% PLA polymer. Immersion in Ringer׳s solution for 4 weeks resulted in formation of corrosion products on the specimens׳ surface, a few percent weight loss and about 50% decrease in bending strength. In vitro studies of β-TCP-15Fe15Mg composite with human osteoblast monocultures and human osteoblast–endothelial cell co-cultures indicated that the composition was biocompatible for the growth and survival of both cell types and cells exhibited tissue-specific markers for bone formation and angiogenesis, respectively.

Highly Dense Mn-Co Spinel Coating for Protection of Metallic Interconnect of Solid Oxide Fuel Cells

The major degradation issues of solid oxide fuel cells (SOFC) are associated with the oxide scale growth and Cr evaporation of the metallic interconnect. To address these challenges, a highly dense spinel oxide coating was fabricated on a ferritic stainless steel interconnect using a cost-competitive ceramic processing route. The nano-scale Mn1.5Co1.5O4 spinel powder was synthesized using a glycine-nitrate method, and the particle agglomerates were effectively disintegrated by a high-energy attrition milling process. The spinel protective coating, which was applied by screen printing, was sintered to a nearly full density, without causing damage to the metallic substrate, by a high-temperature annealing process in a reducing environment, followed by re-oxidation at a moderate temperature. The dense spinel coating remarkably reduced the growth rate of chromia scale and restrained the evaporation of chromium species, as verified by area specific resistance (ASR) measurements and analysis on chromium distribution over the cross-section. Strong adhesion between the coating and substrate was confirmed after 500-hour operation. The sintering mechanism involved in reduction-oxidation heat-treatment was studied based on dilatometry measurements and microstructural features. The implication of the ASR change and the chromium migration for stability of practical SOFC stacks was discussed in detail.

Effect of mechanical activation on the crystallization and properties of iron-rich glass materials

ABSTRACTThe effect of mechanical activation (MA) of the precursor mixture of raw materials and/or the parent glass, on the microstructure and physical and mechanical properties of iron-rich glass-ceramic materials of the system SiO2-B2O3-BaO-Fe2O3, has been studied. MA of the materials is conducted for 0, 2 or 6h using a high energy attrition milling device. Crystallization treatments are given to the parent glass at 650, 750 or 850°C for 5h. Crystallization of the samples is promoted by increased treatment temperature, and especially also by double MA at 850°C. With increasing crystallization temperature, both the density and the compressive strength increase, while porosity decreases. However, at 850°C, prolonged MA decreases both the density and the compressive strength due to an increment in porosity caused by the growth of the BaFe12O19 crystals.

Microstructural features, texture and strengthening mechanisms of nanostructured AA6063 alloy processed by powder metallurgy

Nanostructured AA6063 (NS-Al) powder with an average grain size of ∼100 nm was synthesized by high-energy attrition milling of gas-atomized AA6063 powder followed by hot extrusion. The microstructural features of the consolidated specimen were studied by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques and compared with those of coarse-grained AA6063 (CG-Al) produced by hot powder extrusion of gas-atomized powder (without using mechanical milling). The consolidated NS-Al alloy consisted of elongated ultrafine grains (aspect ratio of ∼2.9) and equiaxed nanostructured grains. A high fraction (∼78%) of high-angle grain boundaries with average misorientation angle of 33° was noticed. Microtexture evaluation by plotting pole-figures and orientation distribution function (ODF) analysis showed Copper and P texture components for both the consolidated Al alloys. Tensile test at room temperature and microhardness measurement revealed that a significant improvement in the strength of AA6063 alloy is obtained through refinement of the grain structure. The strengthening mechanisms are discussed based on the dislocation-based models. The role of high-angle and low-angle grain boundaries on the strengthening mechanisms is discussed.

Surface coating on carbon nanofibers with alumina precursor by different synthesis routes

Alumina-reinforced carbon nanofiber nanocomposites were prepared using different routes; powders mixture, colloidal route and sol–gel process followed by spark plasma sintering (SPS). CNFs/xAl 2O 3 ( x = 10–50 vol.%) were prepared through nanopowders mixing in a high-energy attrition milling. The main limitations in the preparation of this kind of nanocomposites are related to the difficulty in obtaining materials with a homogeneous distribution of both phases and the different chemical nature of CNFs and Al 2O 3, which causes poor interaction between them. A surface coating of CNFs by wet chemical routes with an alumina precursor is proposed as a very effective way to improve the interaction between CNFs and Al 2O 3. An improvement of 50% in fracture strength was found for similar nanocomposite compositions when the surface coating was used. The improved mechanical properties of these nanocomposites are caused by stronger interaction between the CNFs and Al 2O 3.

The influence of attrition milling on carbon dioxide sequestration on magnesium–iron silicate

Present work evaluates the structural changes in olivine (Mg,Fe) 2SiO 4 (deposit Åheim, Norway) generated by mechanical treatment as well as its adsorption properties for carbon dioxide. The high-energy attrition milling was applied for mechanical activation. Identification of the mechanically-induced changes in the mineral was carried out applying various techniques: scanning electron microscopy, Mössbauer spectroscopy, specific surface measurements, carbon dioxide adsorption and Fourier-transformed infrared spectroscopy. The observed changes in the physico-chemical properties illustrate the possibility of the applied activation to modify the surface and/or bulk properties of olivine. Sensitivity for atmospheric CO 2 sequestration as well as sequestration of CO 2 by chemisorption can be derived from the obtained results.

Influence of mechanical activation on combustion synthesis of fine silicon carbide (SiC) powder

The influence of mechanical activation of powder mixtures of Si and C, via high energy attrition milling (up to 12 h), on combustion synthesis of SiC was experimentally investigated. β-SiC fine powder was successfully fabricated in 1.0 MPa N 2 atmosphere without other additional treatments, such as preheating, electric action, or chemical activation. Relatively weak peaks of α-SiC, α-Si 3N 4 and Si 2ON 2 were also found in the final products. The experimental results and their theoretical treatment showed that mechanical activation via high energy ball-milling provides to the initial Si/C powder mixture extra energy, which is needed to increase the reactivity of powder mixture and to make possible the ignition and the sustaining of combustion reaction to form SiC.

Study of the silver ions cementation after mechanical activation of cementator

Thiosulphate leaching of silver is a proposed alternative to cyanide or thiourea leaching for certain types of refractory silver ores and secondary sources. Traditional method for the recovery of rare metals from various sources by hydrometallurgy is leaching followed by cementation onto zinc powder and electrowinning. Silver cementation is an inexpensive and simple way to deposit thin metal films. Cementation of silver onto zinc powder treated by mechanical activation from thiosulphate solutions was studied by measuring of Ag + ions concentration in this work. The high energy attrition and planetary ball milling in methanol was applied for the mechanical activation of zinc powder. The changes of the particle size distribution and surface area of cementator, occurring during mechanical treatment have been registered. The observed changes in the physico-chemical properties illustrate the possibility of the applied activation to modify the surface and/or volume properties of zinc powder and its further application in well-known hydrometallurgical process of cementation. The study was also focused on the changes in the concentration of zinc and pH as a function of reaction time as well as on the morphology of cementation products on zinc powder.

Mechanical induced reaction in Al–CuO system for in-situ fabrication of Al based nanocomposites

Abstract Gradual chemical (displacement) reaction between CuO and Al powders during high-energy attrition milling under a high purity argon atmosphere was studied. Differential thermal analysis (DTA), X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques were employed to study the solid-state reaction. It was shown that the solid-state reaction occurred during mechanical alloying (MA) and resulted in the dissolution of copper into the aluminum lattice and formation of nanometric alumina particles. The reinforcement particles were mostly distributed at the grain boundaries of Al matrix with an average crystallite size of about 50 nm. In DTA curve of the milled powders, a small exothermic peak after Al melting was noticed. The peak became smaller, i.e. less exothermic, with increasing the milling time, indicating that the solid-state reaction occurs gradually during MA. While the oxide particles formed by MA were found to be nanometric with almost uniform size distribution, the reaction product of Al melt and CuO was clustered and ultrafine. This observation indicated the advantage of mechanically induced solid-state reaction (mechanical alloying) over liquid–solid reaction (casting) for in-situ processing of metal matrix nanocomposites.

Mechanical-activation-assisted combustion synthesis of SiC powders with polytetrafluoroethylene as promoter

Mechanical-activation-assisted combustion synthesis of SiC has been conducted with polytetrafluoroethylene (PTFE) as promoters. The mechanical activation of the Si–C reactants with the addition of NH 4Cl as process controlling agent during the high-energy attrition milling could substantially decrease the content of PTFE promoter, which is needed for inducing the Si–C combustion reaction. Ultra-fine β-SiC powders with spherical particles were synthesized at PTFE content as low as 6 wt.%. The combustion synthesized SiC powders have a narrow particle size distribution in the range of 0.5–1 μm.

Nanocrystalline titanium powders by high energy attrition milling

The present investigation deals with the synthesis of nanocrystalline titanium powders by the high energy attrition milling of micron sized titanium powder in an inert atmosphere. Titanium powders of about 12 μm particle size were subjected to high energy attrition milling in an argon atmosphere. Selecting suitable milling parameters, nanosize (< 100 nm) titanium powders were obtained after 15 h of milling. An average particle size of 35 nm was obtained at 30 h of milling after which the particle size stabilized with continuation of milling to 75 h. The powders after milling for various durations were characterized by XRD, SEM, TEM, ICP-AES and DTA and these results are reported and discussed.

Mechanical-activation-assisted combustion synthesis of SiC

Mechanical-activation-assisted combustion synthesis of SiC has been conducted with PVC as promoters. The mechanical activation of the Si–C reactants through high-energy attrition milling could result in substantial decrease of the ignition temperature and the incubation time for the Si–C combustion reaction. Ultra-fine β-SiC powders with equiaxed grains were synthesized at the preheating temperature as low as 1050 °C. The specific surface area (SSA) of the combustion synthesized SiC powders was 4.36 m 2/g, and the average particle size was less than 5 μm.

Synthetic spinel-forsterite refractory aggregates from the sillimanite minerals

Applying the alumina-magnesia-silica equilibrium phase diagram as the fundamental basis, the three sillimanite minerals, kyanite, andalusite and sillimanite, were processed in the presence of magnesia to produce spinel-forsterite refractory aggregates. Both conventional ball milling and high-energy attrition milling were applied to reduce the particle size of the minerals and mix them. Ball milling achieved micrometer size particles, while the attrition milling reduced the particles to the nanometer scale. Firing in air between 1,200° and 1,700 °C produced results that are a combination of the individual mineral decompositions and the spinel/forsterite formation. These effects were separated to address the reaction/densification processes and obtain dense spinel/for sterite refractory aggregates with fine microstructures.

Synthesis of nanosized titanium powder by high energy milling

Titanium powders of about 2 μ particle size were subjected to high energy attrition milling in an argon atmosphere. Selecting suitable milling parameters, nanosize (<100 nm) titanium powders were prepared after 15 h of milling. An average particle size of 35 nm was obtained at 30 h of milling after which the particle size stabilized with continuation of milling to 75 h. The powders after milling for various durations were characterized by TEM, ICP and XRD, and these results are reported and discussed.