Microstructures and Properties of Nanocrystalline NiFe Alloy With and Without Particulate TiC Reinforcement by Mechanical Alloying

In the current study, Ni₅₀Fe₅₀ alloy powders were prepared using a high-energy planetary ball mill. The effects of TiC addition (0, 5, 10, 20, and 30 wt pct) and milling time on the sequence of alloy formation, the microstructure, and microhardness of the product were studied. The structure of solid solution phase, the lattice parameter, lattice strain, and grain size were identified by X-ray diffraction analysis. The correlation between the apparent densities and the milling time is explained by the morphologic evolution of the powder particles occurring during the high-energy milling process. The powder morphology was examined using scanning electron microscopy. It was found that FCC γ (Fe–Ni) solid solution was formed after 10 hours of milling, and this time was reduced to 7 hours when TiC was added. Therefore, brittle particles (TiC) accelerate the milling process by increasing crystal defects leading to a shorter diffusion path. Observations of polished cross section showed uniform distribution of the reinforcement particles. The apparent density increases with the increasing TiC content. It was also found that the higher TiC amount leads to larger lattice parameter, higher internal strain, and lower grain size of the alloy.     

Effect of the method of introduction of Y2O3 into NiAl-based powder alloys on their structure: II. Mechanical activation

Effect of mechanical activation of NiAl powders produced by calcium hydride reduction in an attritor and a ball mill on the specific surface, the oxygen concentration, the strain hardening, and the coherent domain size (CDS) of the powders is studied. It is found that the powder specific surface milled in the attritor for 10–15 h is larger by a factor of 1.7–1.8 and the oxygen concentration in a powder is lower by a factor of 1.35 as compared to the its milling in the ball mill for 150 h. The powders milled in the attritor for 15 h have the level of microstresses higher by a factor of ～2.4 and the CDS smaller by a factor of 2 as compared to the powder treated in the ball mill for 150 h. When milling a powder in the attritor, the milling time decreases by a factor of 10 and the degree of powder refinement increases, which improves the technological characteristics of the powders. As a result of the combination (in one operation) of mechanical activation of an NiAl intermetallic matrix powder in the attritor and the introduction of dispersed particles of a refractory oxide Y₂O₃ powder, the produced composite alloy has a density close to the theoretical one and has no aggregates of dispersed oxide particles at grain boundary junctions. Submicro- and nanosized oxide particles are homogenously distributed in the intermetallic matrix volume, which is characterized by a homogeneous distribution of nickel and aluminum.     

Synthesis of nanocrystalline titanium carbide alloy powders by mechanical solid state reaction

A high-energy ball mill operated at room temperature has been used for preparing titanium carbide (TiC) alloy powders, starting from elemental titanium (Ti) and carbon (C) powders. X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) have been used to follow the progress of the mechanical solid state reaction of Ti and C powders. A complete single phase of fcc-Ti₄₄C₅₆ alloy powders is obtained after a very short milling time (20 ks). The lattice parameter (a ₀ ) of the end product of Ti₄₄C₅₆ was calculated to be 0.4326 nm. The presence of excess starting reactant materials (Ti and/or C atoms) in the final product of the alloy powders could not be detected. The end product of Ti₄₄C₅₆ alloy powders possesses homogeneous, smooth spherical shapes with an average particle diameter of less than 0.5 μm. The internal structure of the particles is marked by fine cell-like features of about 3 nm. On the basis of the results of the present study, the mechanical alloying (MA) process appears to provide a powerful tool for the fabrication of Ti₄₄C{im56} alloy powders at room temperature. The mechanism of mechanical solid state reaction for formation of Ti₄₄C₅₆ alloy powders is discussed. Formerly Lecturer of Materials Science, Mining and Petroleum Engineering Department, Faculty of Engineering, Al-Azhar University, Nasr City 11884, Cairo-Egypt.     

Development of Hydrogenating Powder Alloys for the Electrodes of Alkali Batteries. Part 3. Production Characteristics of Gas-Atomized Powders of Multicomponent Intermetallic Alloys

Alloy powders containing rare earth metals are prepared by the gas atomization method and their structure, surface, technological, and electrochemical properties are studied. Powders of the alloys LaNi_4.5Al_0.5, LaNi_2.5Co_2.4Al_0.1, and (Mm, La)Ni_3.5Co_0.7Al_0.35Mn_0.4Zr_0.05 are prepared with different particle sizes. The morphology, oxygen content and crystal structure of powders in relation to particle size are studied by x-ray analysis, electron microscopy, and surface dispersion spectroscopy. The hydrogen capacity and electrochemical properties of different fractions are determined. It is established that all of the fractions have similar morphology and alloy lattice parameters. The surface of gas atomized powders with less particle size is less contaminated with oxygen compared with larger fractions. At the same time fractions with a particle size <50 μm have poor activity during gas and electrochemical hydrogenation. DTA curves for fractions of fine particles have an additional exothermic peak that may be caused by thermally induced transformation of the amorphous component into crystalline. The coarse fraction of gas atomized powder has the same hydrogen and electrochemical capacity as for fuzzed alloys.     

Correlation of Microstructure,Hardness, and Fracture Toughness of Fe-Based Surface Composites Fabricated by High-Energy Electron Beam Irradiation with Fe-Based Metamorphic Alloy Powders and VC Powders

Iron-based surface composites were fabricated with Fe-based metamorphic alloy powders and VC powders by high-energy electron beam irradiation, and the correlation of their microstructure with hardness and fracture toughness was investigated. Mixtures of metamorphic powders and VC powders were deposited on a plain carbon steel substrate, and then the electron beam was irradiated on these powders without flux, to fabricate surface composites. The composite layers 1.3 to 1.8 mm in thickness contained a large amount (up to 47 vol pct) of hard Cr₂B and V₈C₇ particles formed in eutectic colony regions and inside colonies, respectively. The hardness of the surface composites was approximately 2 to 4 times greater than that of the substrate because of Cr₂B and V₈C₇ particles. According to the microfracture observation of the composite fabricated with mixing 30 wt pct VC powders, microcracks initiated at coarse V₈C₇ particles ins inside colonies as well as at Cr₂B particles in colony regions, and were connected with other microcracks in a zigzag shape. Thus, it showed a higher fracture toughness and hardness twice as high as the composite fabricated without mixing VC powders.     

Superfine and Ultrafine Grinding— A Literature Survey

The growing demand for ultrafine powders, coupled with stringent quality requirements, calls for continuous improvements in all aspects of fine particles production. The high energy costs involved in comminution is also an additional motivator. The equipment most commonly used in fine particles processing and the related process parameters is described. Tumbling ball, stirred, vibratory and fluid energy mills are the most commonly used mill types. A number of factors influence the choice of equipment, including the end-use of the product, required product size distribution, sensitivity of the material to heat, and purity requirements. Stirred ball mills are used in ultrafine grinding because of their high unit outputs, while the low amplitude vibro-energy mills are used because of their low specific energy. Fluid energy mills are economic only in some specific applications as in treating heat sensitive materials, materials for plastics and ceramics where purity and delamination are the most important criteria.     

α″ Martensite and Amorphous Phase Transformation Mechanism in TiNbTaZr Alloy Incorporated with TiO<Subscript>2</Subscript> Particles During Friction Stir Processing

This work studied the formation of the α″ martensite and amorphous phases of TiNbTaZr alloy incorporated with TiO₂ particles during friction stir processing. Formation of the amorphous phase in the top surface mainly results from the dissolution of oxygen, rearrangement of the lattice structure, and dislocations. High-stress stemming caused by dislocations and high-stress concentrations at crystal–amorphous interfaces promote the formation of α″ martensite. Meanwhile, an α″ martensitic transformation is hindered by oxygen diffusion from TiO₂ to the matrix, thereby increasing resistance to shear.     

The structure and properties of aluminum alloys produced by mechanical alloying: Powder processing and resultant powder structures

Mechanical alloying of two aluminum alloy powders to form composite A1-A1₂O₃ powders has been studied. Changes in powder microstructure with processing are reported and interpreted. Mechanical alloying proceeds by the continual cold welding and fracturing of the constituent powder particles when subjected to the large compressive forces of a high speed mill. A suitable organic surfactant must be added so that a balance between cold welding and fracturing is obtained. The organic surfactant is embedded and finely distributed in the powder particles during mechanical alloying and is converted to discrete A1₄C₃ particles after hot pressing. The establishment of steady state processing conditions, characterized by equiaxed powder particles, a constant particle size distribution and a saturation hardness, is found to depend on the size distribution of the initial powders. The oxide particles formed and distributed during mechanical alloying are equiaxed, small (30 nm) and homogeneously distributed with a volumetric center to center distance of about 60 nm. Formerly Graduate Research Assistant in the Department of Materials Science and Engineering at Stanford.     

Correlation of microstructure and abrasive and sliding wear resistance of (TiC,SiC)/Ti-6Al-4V surface composites fabricated by high-energy electron-beam irradiation

This study is concerned with the correlation of microstructure and abrasive and sliding wear resistance of (TiC,SiC)/Ti-6Al-4V surface composites fabricated by high-energy electron-beam irradiation. The mixtures of TiC, SiC, Ti + SiC, or TiC+SiC powders and CaF₂ flux were deposited on a Ti-6Al-4V substrate, and then an electron beam was irradiated on these mixtures. The surface composite layers of 1.2 to 2.1 mm in thickness were homogeneously formed without defects and contained a large amount (30 to 66 vol pct) of hard precipitates such as TiC and Ti₅Si₃ in the martensitic matrix. This microstructural modification, including the formation of hard precipitates in the surface composite layer, improved the hardness and abrasive wear resistance. Particularly in the surface composite fabricated with TiC + SiC powders, the abrasive wear resistance was greatly enhanced to a level 25 times higher than that of the Ti alloy substrate because of the precipitation of 66 vol pct of TiC and Ti₅Si₃ in the hardened martensitic matrix. During the sliding wear process, hard and coarse TiC and Ti₅Si₃ precipitates fell off from the matrix, and their wear debris worked as abrasive particles, thereby reducing the sliding wear resistance. On the other hand, needle-shaped Ti₅Si₃ particles, which did not play a significant role in enhancing abrasive wear resistance, lowered the friction coefficient and, accordingly, decelerated the sliding wear, because they played more of the role of solid lubricants than as abrasive particles after they fell off from the matrix. These findings indicated that high-energy electron-beam irradiation was useful for the development of Ti-based surface composites with improved abrasive and sliding wear resistance, although the abrasive and sliding-wear data should be interpreted by different wear mechanisms.     

Crystal structure of the intermetallics produced by a calcium hydride method

Practically important intermetallics TiNi, NiAl, Ni₃Al, TiAl, and Zr₃Al₂ (St 101 alloy for gas absorbers) produced by the calcium hydride method are comprehensively studied. The total content of impurities in these intermetallic powders does not exceed 1 wt %, and the fraction of the main phase in compounds with a narrow homogeneity region is at least 93?C96 vol %. The main phases in all powders under study have a defectless crystal lattice, and their lattice parameters point to a low content of dissolved impurities in all intermetallics except for Zr₃Al₂. A high degree of homogeneity of the phase compositions of the intermetallic powders is supported by a scanning electron microscopy investigation.     

Effect of electrolysis conditions on the formation,structure, and magnetic properties of a finely divided iron-cobalt alloy

Conclusions An investigation was carried out into the effect of electrolyte concentration and current density on current efficiency in the electrodeposition of Fe, Co, and Fe-Co alloy powders. It was established that raising the electrolyte concentration from 6.65 to 26.62 g/liter of Fe²⁺ + Co²⁺ increases current efficiency, whose maximum value is about 90%. The highest current efficiency is attained at i_c of 20–30 A/dm². Changing the electrolyte concentration and current density does not significantly affect the composition of alloy deposits. At an iron-to-cobalt ion content ratio in the electrolyte of 11 the rate of discharge of Fe²⁺ during alloy formation in the twolayer bath is greater than that of Co²⁺. X-ray structural analysis revealed that the greatest changes in the internal structure of a very finely divided iron-cobalt alloy take place at low electrolyte concentrations. That raising the electrolyte concentration facilitates alloy formation is confirmed by a decrease in the degree of defectiveness of the particles and a stabilization of the crystal lattice parameter of the alloy; i_c does not have such an effect on the structure of the alloy. Magnetometric measurements demonstrated that the coercive force of alloy powders is greater at higher densities of dislocations in their particles.Translated from Poroshkovaya Metallurgiya, No. 8(224), pp. 5–11, August, 1981.     

Preparing Microcomposite Powders Doped with Antimony Dioxide and Properties of Thick Films Based on Those Powders

The goal of the work reported here was to develop a method of applying glass nanolayers of variable thickness to Sn_0.9Sb_0.1O₂ particles and to investigate how this affects the electrical properties of thick-film resistors. We prepared Sn_0.9Sb_0.1O₂ powders by calcinating coprecipitated tin and antimony hydroxides. Thin layers of aluminum, barium, and boron compounds were then precipitated from aqueous solutions onto powder particles. Nanolayers of glass in the BaO ― Al₂O₃ ― B₂O₃ system were obtained by dissolution followed by heat treatment. Resistive thick films made from such microcomposite powders have a higher resistivity than do those prepared by traditional methods and that resistivity changes little after repeated heat treatments. The thermal coefficient of electrical resistance decreases with increasing thickness of the glassy layer on the surface of the conducting particles.     

The Interface of TiB<Subscript>2</Subscript> and Al<Subscript>3</Subscript>Ti in Molten Aluminum

In the grain refinement of aluminum, Al₃Ti and TiB₂ particles are introduced to reduce the casting grain size down to 200 micrometer level, which makes cold working possible. The particles are brought in by the addition of Al-Ti-B-type master alloys. It is generally believed that TiB₂ particles are stable and nucleate α-Al grains in solidification in the presence of titanium in solution from the dissolution of Al₃Ti particles in the master alloys. The titanium in solution either forms Al₃Ti layers on the surface of TiB₂ particles to promote the nucleation of α-Al grains or remains as solute to restrict the growth of α-Al grains in solidification. However, a consensus on a grain refinement mechanism is still to be reached due to the lack of direct observation of the three phases in castings. This paper presents finding of the TiB₂/Al₃Ti interfaces in an Al-Ti-B master alloy. It demonstrates a strong epitaxial growth of Al₃Ti on the surface of TiB₂ particles, a sign of the formation of an Al₃Ti layer on the surface of TiB₂ particles in grain refinement practice. The Al₃Ti layer has a crystal coherency with α-Al and hence offers a substrate for heterogeneous nucleation of α-Al grains. However, the layer must be dynamic to avoid the formation of compounded Al₃Ti and TiB₂ particles leading to the loss of efficiency in grain refinement.     

NiAl powder alloys: I. Production of NiAl powders

The influence of five methods of production of Ni₅₀Al₅₀ powder alloys on the processes occurring during reactive alloy formation of nickel monoaluminide during heating is considered. It is shown that, when powder mixtures obtained by agitation in ball mills and cladded composite powders with a low level of internal stresses are used, it is possible to produce a material with a nearly equilibrium phase composition in the course of reactive sintering due to an exothermic effect with the participation of a liquid phase (aluminum melt) in the reaction. The sintered material is porous and has an island structure. Mechanical alloying in a high-energy ball mill (attritor) results in the formation of layered Ni/Al granules with a developed interface and a high level of internal stresses and defects, which makes it possible to decrease the temperatures of initiation of reactive interaction by ∼300°C. This interaction develops in the solid phase according to a slow diffusive mechanism leading to the formation of intermediate nickel aluminides and hindering the achievement of equilibrium phase composition. The microingot granules (∼80 wt % particles 100–400 μm in size) produced by melt spraying by gases (N, Ar) has the composition of the melt, but grain boundaries are depleted of aluminum in comparison with the volume. The NiAl powders (∼90 wt % particles <40 μm in size) produced by combined hydride-calcium reduction are characterized by a highly homogeneous nickel and aluminum distribution, and their composition is close to equilibrium. These two types of powders are selected as the initial material for investigating the compacting and production of NiAl-based alloys.     

Preparing Microcomposite Powders Doped with Antimony Dioxide and Properties of Thick Films Based on Those Powders

The goal of the work reported here was to develop a method of applying glass nanolayers of variable thickness to Sn_0.9Sb_0.1O₂ particles and to investigate how this affects the electrical properties of thick-film resistors. We prepared Sn_0.9Sb_0.1O₂ powders by calcinating coprecipitated tin and antimony hydroxides. Thin layers of aluminum, barium, and boron compounds were then precipitated from aqueous solutions onto powder particles. Nanolayers of glass in the BaO ― Al₂O₃ ― B₂O₃ system were obtained by dissolution followed by heat treatment. Resistive thick films made from such microcomposite powders have a higher resistivity than do those prepared by traditional methods and that resistivity changes little after repeated heat treatments. The thermal coefficient of electrical resistance decreases with increasing thickness of the glassy layer on the surface of the conducting particles.

     

微量Fe元素对氧化钨粉还原过程的影响

采用液–固掺杂结合两步氢还原法分别制备未添加和添加质量分数0.1％和1.0％Fe的金属W粉,研究了微量Fe元素对WO3还原过程及产物结构特征的影响.结果表明:WO3前驱体粉体经掺杂和煅烧处理后,在其颗粒表层晶格中形成了含Fe固溶体;在氢气还原过程中,Fe的固溶能够降低WO2.9→WO2和WO2→W的还原温度,促进WO3...     

Clssified refractory compound powders

Conclusions Technical quality requirements for refractory compound abrasive powders and optimum conditions for the comminution and classification of some refractory compound powders have been determined. A study was made of some physicomechanical properties (strength, abrasive ability, specific surface, and apparent density) of TiB₂, TiC, and TiN powders. The existence of a method for the manufacture of refractory compound abrasive powders and data yielded by a study of their physicomechanical characteristics will enable these powders to be used in the near future on a wider scale in tool production.Translated from Poroshkoyaya Metallurgfya, No. 6(234), pp. 92–98, June, 1982.     

New method to prepare iron particles with different morphologies: a way to get high green strength metal compacts

Abstract

Metaliron powders of well controlled size and morphology were synthesised by thermal decomposition under hydrogen of precipitated ferrous oxalates. Green compacts were prepared by uniaxial pressing of metal powders at 290 MPa. The bending green strengths of compacts were measured.

The precipitation of β-FeC₂O₄.2H₂O oxalate from ammonium oxalate gives rise to the formation of spherical particles by aggregation ofelongated grains. Thermal decomposition of this oxalate from 400 to 500°C under hydrogen permits metal iron particles with a rough surface to be obtained. Decomposition occurring above 500°C induces a smoothness of the particle surface. Metal particles synthesised at 500°C show both surface roughness and micrometer sized primary grains.This specific microstructure has allowed the highest value ofcompact green strength (31·7 MPa) to be obtained.

Acicular shaping of the β-FeC₂O₄.2H₂O particles precipitated from oxalic acid involves, after decomposition, an increase in the surface roughness and shape irregularity of the metal particles, owing to an entanglement of the elementary grains. An exceptional value (about 60 MPa) for the metal compact green strength was thus obtained for this type of powder.     

Some characteristics of the cold densification of wurtzite boron nitride powders under conditions of high pressures

Conclusions Determinations were made, using mercury porosimetry methods, of the specific surfaces and mean particle sizes of the main fractions of wurtzite boron nitride powders and compacts. It was found that in pressing in the pressure range 1.0–10.0 GPa densification was accompanied by intense comminution of BN_w particles. The re-pressing of BN_w powders granulated after being pressed under a pressure of 4.3 GPa was satisfactorily described by M. Yu. Bal'shin's equation.Translated from Poroshkovaya Metallurgiya, No. 10(238), pp. 6–10, October, 1982.     

Effect of the method of introduction of Y2O3 into NiAl-based powder alloys on their structure: I. Agitation in a ball mill

The effect of the sintering temperature (1100–1400°C) of NiAl alloy samples with oxide Y₂O₃ produced by hydrostatic pressing on their structure and phase composition and the distribution of oxide particles in a NiAl-based intermetallic matrix alloyed with ～0.5 at % Fe is considered. It is found that dispersed oxide particles in the compact material prepared from a mixture of oxide Y₂O₃ powder and a NiAl alloy (produced by calcium hydride reduction of a mixture of nickel and aluminum oxides) powder in a standard ball mill are nonuniformly distributed in the volume. The morphology of oxides changes during sintering: sintered samples contain rounded particles, which differ strongly from the clearly faceted angular particles of oxide Y₂O₃ added to a mixture (they represent conglomerates of single crystals). In the sintered samples, large aggregates of oxides are revealed along grain boundaries. Mass transfer is possible at the NiAl/Y₂O₃ interface in the system: it leads to partial substitution of aluminum and/or iron atoms for yttrium atoms in the Y₂O₃ lattice and to the formation of submicroscopic particles of (Fe,Al)₅Y₃O₁₂-type oxides.