Compacted Powder Mixtures Research Articles

Formation of intermetallic compounds during reaction between Ti and Al–Mg alloys with various Mg contents

The reactions between Ti and Al–Mg alloys were systematically investigated by heating the Ti/Al–Mg alloy powder mixture compacts with Mg contents ranging from 5.09 to 40.36 wt.% at 660 °C. Mg element in the Al–Mg alloys contributed to the breakage of the oxide films on the surfaces of the Ti and Al–Mg alloy powders, thus, promoting the reactions. In the samples with Mg contents varying from 5.09 wt.% to 25.93 wt.%, the first-formed intermetallic compound was Al18Ti2Mg3, and then Al3Ti generated at the Al18Ti2Mg3/Ti interface. Since the Mg content in the Al–Mg melts decreased during the subsequent heating process, the previously formed Al18Ti2Mg3 in the Ti/Al–5.09Mg sample transformed into Al3Ti accompanied by the reaction of Al with Ti to newly form Al3Ti, generating a single Al3Ti phase. In contrast, the new formation of Al3Ti and its transformation to Al18Ti2Mg3 proceeded continuously in the Ti/Al–13.54Mg and Ti/Al–25.94Mg samples, resulting in a mixture of Al18Ti2Mg3 and a little Al3Ti residue. In the Ti/Al–40.54Mg sample, Al3Ti was the unique reaction product throughout the heating process. The final Al3Ti particles in the Ti/Al–5.09Mg sample were in a blocky shape, while they were in a plate-like form in the Ti/Al–40.54Mg sample, which was caused by the enhanced growth anisotropy due to the decreased interfacial energy between Al3Ti particles and Al–Mg melts with the increase of Mg content. A twin plane re-entrant mechanism was suggested for the growth of Al18Ti2Mg3 particles, weakening the anisotropic growth caused by the directional supply of Ti atoms, and contributing to the blocky morphology of Al18Ti2Mg3 particles. In addition, the volume difference between the formed Al18Ti2Mg3 and consumed Ti was greater than that between the Al3Ti and Ti, and the Al18Ti2Mg3 has worse plasticity than the Al3Ti, resulting in the Al18Ti2Mg3 reaction product fracturing more easily during thickening, thus forming a petal-like structure, but the Al3Ti product being in an almost continuous layer.

Effect of Silicon on the Surface Modification of Al-Cr Powder Cathodes Subjected to Vacuum Arc Treatment

Al-Cr and Al-Cr-Si composite cathodes were obtained by the hot compaction of aluminum, chromium, and silicon powder mixtures. The phase transformations in the surface layer of the Al-Cr-Si composite cathodes subjected to the arc heating were considered. The elemental and phase compositions of the modified cathodes’ surfaces were studied using X-ray diffraction, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The effect of the silicon addition on the structural evolution in the cathode surface during arc evaporation is shown. It was found that an arc impact on the cathode surface resulted in the melting and consequent crystallization of the multiphase mixture of intermetallic compounds and eutectic in the cathode surface layer. Cathode surface layers were found to be depleted of aluminum and silicon due to the ejection of these elements in drop form from the Al-Si liquid layer on the cathode surface. This can result in the change in the elements ratio in the deposited coating as compared with that in the cathode and thus influence the coated tools’ durability.

Standoff Detection of Oil and Powder Mixtures at 12 Meters Using a Tunable Quantum Cascade Laser-Based System with a Close Focus Telescope and Uncooled Infrared Detector

We have designed and demonstrated a quantum cascade laser (QCL) based standoff system that utilizes an uncooled mercury cadmium telluride (MCT) detector with lock-in signal processing for chemical identification at a distance of 12.5meters in indoor ambient light conditions. In the system, a tunable quad-QCL operating (1MHz) in quasi-continuous wave mode between 8.45 and 10.03μm (∼1182 to 1000 cm-1) serves as the active mid-infrared source for remotely interrogating mineral, powder, and thin film oil samples including powder mixtures (6, 12.5, 25, and 50%) of crystalline quartz (SiO2) in KBr. Light as reflected from a given sample is collected using a 10-inch (25.4cm) Dall Kirkham telescope and coupled with ZnSe optics to an uncooled MCT detector. The mixture dependence of the highly transparent KBr and strongly absorbing quartz was found to fit a modified version of the Schatz reflectance model for compacted powder mixtures. All reflectance spectra reported are relative to an Au-coated diffuse reflector. A NIST traceable polystyrene standard reflector was also used to determine the QCL wavelength tuning range and calibration.

Effect of the Hot Deformation Conditions on Structure and Mechanical Properties of AlCr/AlCrSi Powder Composites

Aluminum matrix composites usually contain strengthening particles of refractory compounds (SiC, Al2O3) that do not react with the Al matrix. There is a problem in producing the Al matrix composite with inclusion of metals that can generate intermetallic compounds with aluminum. In this case, a conventional sintering of powder mixtures results in high porosity due to volume growth. That is why some new methods of producing dense Al matrix composites are required. A possibility to create a dense powder Al-based composite containing hard components, such as chromium and silicon, without using the sintering process, is considered. This paper presents study results of structural and mechanical properties of Al-Cr and Al-Cr-Si composites produced by hot compaction of powder mixtures. An analysis of the relationship between mechanical properties and structures of Al-Cr and Al-Cr-Si composites is carried out. Optimal values for thermomechanical processing modes that ensure sufficient strength and plasticity are determined. It is shown that strong bonding of the aluminum particles occurs under hot deformation, and an aluminum matrix is formed that provides acceptable composite bending strength as a result. The presence of chromium and silicon hard inclusions is not a significant obstacle for aluminum plastic flow. Al-Cr and Al-Cr-Si composites produced by hot deformation of the powder mixtures can be used as cathode material for the deposition of wear-resistant nitride coatings on metalworking tools.

Interface characterization of Al/SiCp compacts

In the last decade, several authors and scientists are interested more and more to understand the phenomena which are take place at aluminum matrix and silicon-carbide interface. This type of composite material is especially used in aerospace and automotive industries which involve high temperature applications. Aluminum metal matrix composites containing 5,15,25 weight % SiCp were processed by powder mettalurgy route. The interaction between metallic matrix (aluminum) and particulate ceramic reinforcement (silicon-carbide) was studied. At the beginning the solid-state reaction behavior of the Al/SiC powder mixture compacts was investigated. The density, porosity, compressibility of Al-SiCp composites were calculated. Maximum densification of the composite material reinforced with 5% SiC is obtained at a compactation pressure of 420 MPa (94.5%). For 15% SiC content densification increase with higher compactation pressure given the density values of 95.66% and 96.46% for the 25% SiC composite. Conventional scanning electron microscopy revealed a faceted interface between SiC particulate and Al matrix. This chemical reaction at the interface is the result of dissolution of silicon carbide particulates in aluminum matrix during the liquid sintering process at high temperature:1100,1300,1450 and 1750°C in different sintering atmospheres. For intermetallic compounds identification was used an energy dispersive X-ray spectroscopy (EDX) investigation. The presence of compounds and phases such as: Al4C3, Al4O4C, Al4SiC4, SiO2, Al2O3, confirmed by X-ray diffraction analysis is given by different sintering temperature. It is important to know the structure and chemical composition of the interface and near to the interface zone for study the mechanical properties of the reinforced metal matrix composites.

The Pressure Compaction of Zr-Nb Powder Mixtures and Selected Properties of Sintered and KOBO-Extruded Zr-xNb Materials.

Materials were obtained from commercial zirconium powders. 1 mass%, 2.5 mass% and 16 mass% of niobium powders were used as the reinforcing phase. The SPS method and the extrusion method classified as the SPD method were used. Relative density materials of up to 98% were obtained. The microstructure of the sintered Zr-xNb materials differs from that of the extruded materials. Due to the flammability of zirconium powders, no mechanical alloying was used; only mixing of zirconium and niobium powders in water and isopropyl alcohol. Niobium was grouped in clusters with an average niobium particle size of about 10 μm up to 20 μm. According to the Zr-Nb phase equilibrium system, the stable phase at RT was the hexagonal α-phase. The tests were carried out for materials without the additional annealing process. The effect of niobium as a β-Zr phase stabilizer is confirmed by XRD. Materials differed in their phase composition, and for both methods the β-Zr phase was present in obtained materials. A very favorable effect of niobium on the increase in corrosion resistance was observed, compared to the material obtained from the powder without the addition of niobium.

Internal friction of Ni-Al intermetallic compound formation in sintering process

The Ni-Al intermetallic compounds, as important high-temperature structural materials, have clear target requirements in a number of fields. Powder metallurgy is an important candidate for preparing the Ni-Al intermetallic compounds. Clarifying the formation and transformation process of Ni-Al intermetallic compounds in sintering process and determining the solid diffusion reaction temperature and types of intermetallic compounds are greatly important for tailoring sintering process and optimizing product quality. In this paper, the internal friction behaviors of Ni-Al powder mixture compacts in the sintering process are systematically investigated by the internal friction technique. A typical internal friction peak is observed in the internal friction-temperature spectrum. The peak height decreases with the measuring frequency increasing, but the peak temperature is independent of frequency. Moreover, the internal friction peak shifts toward higher temperature and the peak height increases as the heating rate increases. It is reasonable that the internal friction peak belongs to the typical phase transformation internal friction peak which is associated with the formation of intermetallic compounds NiAl<sub>3</sub> and Ni<sub>2</sub>Al<sub>3</sub> in the heating process. Furthermore, the microstructure of the Ni-Al powder mixture can be tailored by mechanical ball-milling. The internal friction peak shifts toward lower temperature and the peak height decreases with the ball-milling time increasing, which indicates that the solid diffusion reaction can be activated at lower temperature with a slower reaction rate. This decrease is related to the refinement of powder particles, the lamellar formation of powder mixture, the enhancement of solid solution degree and surface energy, and the shortened atomic diffusion distance due to the mechanical ball-milling. It is also indicated that the mechanical ball-milling can effectively reduce the initial temperature of solid diffusion reaction, thus lowering sintering temperature.

High-Density Mo–W–Cu Pseudoalloys Based on Homogenous Mo–25% W Powder Alloy Produced by Reducing Oxide Powders in Moving Layers

The article aimed to obtain a structural material with increased plasticity and density of 98.5–99.5% based on (Mo–25% W)–20 vol.% Cu pseudoalloys with a homogeneous refractory skeleton obtained by a single-time pressing and sintering of the dispersed mixture at temperatures 1400–1500°C. The production of a dispersed granulated Mo–25% W alloy with a powder particle size of 0.1–0.3 μm through the decomposition of complex ammonium paramolybdate and paratungstate salts into oxide compounds xWO3 · yMoO3 with their subsequent reduction by hydrogen in a rotary chamber was studied. Considering the temperature and decomposition time of complex salts in the moving layers, the physical and technological properties (such as phase composition, oxygen content, specific surface, bulk density, and tap density) of complex oxide powders xWO3 · yMoO3 and metal Mo– 25% W powders after reduction by hydrogen were compared with the corresponding properties of powders obtained in a stationary tube furnace in fixed layers. Temperature dependencies of porosity in (Mo–25% W)–20 vol.% Cu pseudoalloys after sintering at the temperature between 900 and 1500°C has been examined. It has been established that compaction of dispersed powder mixtures of (Mo–25% W)–20 vol.% Cu and homogenization of Mo–25% W alloy after sintering begin at the temperature 300°C lower than when sintering mechanical mixtures of commercial metal powders. It has been shown that (Mo–25% W)–20 vol.% Cu pseudoalloys obtained by liquid-phase sintering at 1500°C for 1 hour have the following characteristics: at 20°C, the ultimate tensile strength σt == 490 MPa, relative elongation δ = 1.1, Brinell hardness HB = 3.3 GPa, and at 500°C— σt == 370 MPa, δ = 4.4, and HB = 2.7 GPa.

RESEARCH OF THE MECHANISM OF SEALING POWDER MIXTURES BASED ON SILICON CARBIDE IN EXPLOSIVE PRESSING

The effects of the metal binder content and parameters of shock-wave compression on the compaction of SiC-Ti powder mixtures under explosive loading were investigated; microstructure of the obtained materials; The prevailing mechanisms of compaction of powder mixtures of silicon carbide with titanium during explosive pressing are revealed.

On the processing properties and friction behaviours during compaction of powder mixtures

ABSTRACT Iron-based powder mixtures were prepared by dry and wet mixing method. The friction properties during compaction were tested by measuring the internal and external friction coefficient. The test results showed that the wet mixing process could realise the homogeneity of lubricant and improve the processing properties of the powder mixtures. With 0.6 wt-% lubricants, wet mixing powder mixtures have a flow rate of 29.6 s/50 g, an apparent density of 3.18 g cm–3, a repose angle of 35.5°, and the friction coefficient during the compaction is 0.223. An equation to calculate the total (both internal and external) friction forces during the compaction process is proposed, and then the factors influencing the friction coefficient during compaction were quantitatively analysed.

Effect of the Operational Conditions in the Characteristics of Ceramic Foams Obtained from Quartz and Sodium Silicate.

Ceramic foams were fabricated without using melting pots through the direct foaming of compacted powder mixtures of commercial quartz (SiO2) with fluxing agents (Na2CO3 and CaO) and a foaming agent (Na2SiO3·5H2O) at a relatively low temperature range (850−870 °C). The effects of the pressing pressure of the powders, the foaming time, foaming temperature, and mixture content were evaluated. The obtained cellular solid materials presented an acceptable volumetric expansion at a pressing pressure of 4 t. The materials only presented porosity at a minimum temperature of 850 °C and at a minimum time of 30 min. All the foamed samples showed an acceptable symmetric expansion and non-appreciable fissures. The study of the mixture content through the statistical software MODDE® shows that the porosity of the samples was principally affected by the Na2SiO3 content and the foaming temperature. The samples obtained at the optimum controlling factors proposed by this statistical software presented an apparent density, porosity, and mechanical strength of 1.09 ± 0.03 g/cm3, 56.01% ± 1.12%, and 3.90 ± 0.16 MPa, respectively. Glass and ceramics foams such as those obtained in this work become attractive as insulation materials in applications where high temperatures occur due to their higher melting points.

The Effect of Heating on Phase Composition of the Cr<sub>3</sub>C<sub>2</sub>- Ti System Hard Alloys Fabricated by the Explosive Compaction of Powder Mixtures

The article reports findings on theoretically-calculated data and experimental results obtained with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy methods of the analysis of hard alloys produced by the explosive compaction of the Cr3C2 chromium carbide powders with titanium, first in the original condition and then after heating to 1200 °C. It was established that when heated to 600 °С the phase composition of hard alloys does not change and corresponds to the composition of the original components of the powder mixture. When the heating temperature was increased to 650 °С, new fine powder fractions emerged at the “chromium carbide – titanium” interface. At the temperature of 700 °С two separate diffusion layers emerged and grew in the opposite directions. Due to this growth the source phases in the alloy fully disappeared at 1200 °С and two equilibrium phases were formed.

Influence of bulk and interfacial properties on shock compression of metal powders. I. Interaction of a pair of particles

This paper studies the physics of shock compaction of metallic powder mixtures by focusing on two particles interacting under conditions of high compressive strain rates. Particle-particle interactions are simulated using a sharp interface Eulerian approach. Specifically, the present work seeks to understand how the disparity in bulk material properties such as yield strength and impedance leads to differences in spreading, heating, and contact area of the materials. In addition, the effects of interfacial phenomena such as friction and interfacial melting are examined using the sharp interface framework. The results show that the extent of interfacial contact between the materials is affected by material deformation and jetting. Of the material properties studied, the impedance mismatch exerts the highest influence on the heating of materials. Material yield strength also plays a significant role; the melting of materials is shown to play a minor role in the spreading and evolution of contact of the materials for the shock strengths tested. By focusing on two particles, this work provides insights elucidating the physics of shock compaction of powder mixtures, specifically the influence of bulk and interfacial properties on the extent of interfacial contact between dissimilar materials.

Foundations of the Fabrication Technology of Wear-Resistant Coatings Made of Mixtures of Chromium Carbide Powders with a Metallic Binder by Explosive Pressing

Experimental data on the explosive compaction of powder mixtures of chromium carbide (Cr3C2) with metals (Ti, Ni, Cu) are presented, their theoretical explanations are given, and scientifically substantiated principles of the composition selection and development of the explosive fabrication of wear-resistant antifriction chromium carbide hard alloys and coatings are formed on this basis. The explosive pressing of powder mixtures was performed according to the scheme with the use of a plane normally incident detonation wave in a broad range of loading parameters (the powder heating temperature in shock waves was varied in experiments from 200 to 1000°C, while the maximal pressure of the shock-wave compression varied from 4 to 16 GPa). To analyze the phase transformations, the numerical thermodynamic simulation of the phase equilibrium was performed applying the Thermo-Calc software complex. The microstructure and the chemical and phase compositions were investigated using an Axiovert 40 MAT optical microscope (Carl Zeiss, Germany), Versa 3d and Quanta 3D FEG scanning electron microscopes (FEI, United States), BS 540 (Tesla, Czech Republic) and Titan 80–300 and Techai G2 20F (FEI, United States) transmission electron microscopes, and a Solver Pro atomic force microscope (OOO NT-MDT, Zelenograd). The temperature stability and oxidation resistance at elevated temperatures of materials formed by the explosion were investigated by thermogravimetric analysis using an STA 449 F3 Jupiter device (NETZSCH, Germany) in synthetic air upon heating to 1500°C. Tribotechnical tests were performed using an MI-1M friction machine (MEZIMiV, Moscow) according to the pin–ring scheme with digging in distilled water. Mechanisms of compaction and formation of strong boundaries between the particles of powder materials during the explosive pressing are described. It is shown that chromium carbide hard alloys with a titanium binder formed by explosion retain their phase composition invariable, do not oxidize to 600°C, and have considerably better antifriction properties and wear resistance when compared with SGP-0.5 and KKhN-20 materials lubricated with water, which have been applied in friction pairs until now.

FUNDAMENTALS OF WEAR-RESISTANT COATING PRODUCTION FROM CHROMIUM CARBIDE POWDER MIXTURE WITH BINDER METAL BY EXPLOSIVE COMPACTION

The article presents experimental data on explosive compaction of chromium carbide (Cr3C2) powder mixtures with metals (Ti, Ni, Cu) provided with theoretical explanations. These data were used as a basis for stating science-based principles of composition selection and technology development to produce antifriction wear-resistant chromium carbide hard alloys and coatings by explosion. Explosive compaction of powder mixtures was carried out according to a scheme using a normally incident plane detonation wave in a wide range of loading parameters (powder heating temperature in shock waves varied from 200 to1000 °Cand maximum shock compression pressure varied from 4 to 16 GPa during experiments). Phase transformation analysis was carried out by the numerical thermodynamic modeling of phase equilibrium using the Thermo-Calc software. Microstructure, chemical and phase compositions were studied using optical («Axiovert 40МАТ» by CarlZeiss,Germany), scanning («Versa 3D» and «Quanta 3D FEG» byFEI,USA), transmission («BS 540» byTesla,Czech Republic, «Titan 80-300» and «Tecnai G2 20F» byFEI,USA) electron microscopes and «Solver Pro» atomic force microscope (LLC «NT-MDT», Zelenograd). Temperature stability and oxidation resistance at elevated temperatures of the materials obtained by explosion was studied using thermogravimetric analysis (TGA) using the «STA 449 F3 Jupiter» instrument (NETZSCH, Germany) in the synthetic air environment when heated to1500 °C. Tribological tests were carried out on the MI-1M friction machine (MEZIMiV,Moscow) according to the pin-on-ring scheme with plunging in distilled water environment. The mechanisms of consolidation and formation of strong boundaries between powder material particles during explosive compaction are described. It is shown that hard alloys of chromium carbide with titanium bond obtained by explosion retain their phase compositions without any changes and resist to oxidation up to600 °C, and also have significantly better anti-friction properties and wear resistance than the SGP-0,5 and KHN-20 materials used in water-lubricated friction couples until the present time.

Densification Mechanism, Elastic-Plastic Deformations and Stress-Strain Relations of Compacted Metal-Ceramic Powder Mixtures (Review)

Abstract The basic purpose of compaction is to obtain a green compact with sufficient strength to withstand further handling operations. The strength of green compact is influenced by the characteristics of the powders (apparent density, particle size and shape, internal pores etc.), the processing parameters (applied force, pressing type, and temperature) and testing conditions (strain rate etc.) Successful powder cold compaction is determined by the densification and structural transformations of powders (metallic powders, ceramic powders and metal-ceramic powder mixtures) during the compaction stages. In this paper, for understanding the factors that determine a required strength of compacted metal-ceramic powder mixtures, we present the densification mechanisms of different mixtures according to densification theories of compaction, the elastic-plastic deformations of mixture powders, the stressstrain relations and the relaxation behavior of compacted metal-ceramic composite parts and the particularities of each of them.

Compaction of Metal-Ceramic Powder Mixtures. Part.2

Compaction of Metal-Ceramic Powder Mixtures. Part.2

Formation of Hard Alloys of Chromium Carbide and Titanium Powder Mixtures by Explosive Pressing

The production of a new type of hard alloys by explosive compaction of chromium carbide (Cr3C2) and titanium powder mixtures was investigated. The phase composition of the fabricated alloys was studied using scanning electron probe microanalysis. The chemical composition of the alloy components does not change, and no redistribution of the elements was observed. The formation characteristics of the interfaces between the material components during shock wave processing were investigated using electron microscopy. The explosion compaction of high melting carbide and metal powder mixtures results in the formation of consolidated hard alloys during the compaction stage.

Numerical modelling of shock-induced chemical reactions (SICR) in reactive powder mixtures using smoothed particle hydrodynamics (SPH)

Shock compaction of reactive powder mixtures to synthesize new materials is one of the oldest material processing techniques and has been studied extensively by several researchers over the past few decades. The quantitative connection between the shock energy imparted and the extent of reaction that can be completed in the small time window associated with the passage of the shock wave is complicated and depends on a large variety of parameters. In particular, our understanding of the complex interplay between the thermo-elasto-viscoplastic behaviour of the granular constituents and their temperature dependent, diffusion-limited reaction mechanism may be enriched through careful numerical simulations. A robust numerical model should be able to handle extremely large deformations coupled with diffusion mediated fast reaction kinetics. In this work, a meshfree discrete particle numerical method based on smoothed particle hydrodynamics (SPH) to simulate shock-induced chemical reactions (SICR) in reactive powder mixtures is proposed. We present a numerical strategy to carry out reactions between reactant powder particles and partition the obtained products between the particles in a manner that accounts for the requirement that the total mass of the entire system remains constant as the reactions occur. Instead of solving the reaction–diffusion problem, we propose a ‘pseudo-diffusion’ model in which a distance dependent reaction rate constant is defined to carry out chemical reaction kinetics. This approach mimics the actual reaction–diffusion process at short times. Our numerical model is demonstrated for the well-studied reaction system Nb + 2Si NbSi2. The predicted mass fractions of the product obtained from the simulations are in agreement with experimental observations. Finally, the effects of impact speed, particle arrangement and mixing ratio on the predicted product mass fractions are discussed.

An in situ Study of NiTi Powder Sintering Using Neutron Diffraction

This study investigates phase transformation and mechanical properties of porous NiTi alloys using two different powder compacts (i.e., Ni/Ti and Ni/TiH2) by a conventional press-and-sinter means. The compacted powder mixtures were sintered in vacuum at a final temperature of 1373 K. The phase evolution was performed by in situ neutron diffraction upon sintering and cooling. The predominant phase identified in all the produced porous NiTi alloys after being sintered at 1373 K is B2 NiTi phase with the presence of other minor phases. It is found that dehydrogenation of TiH2 significantly affects the sintering behavior and resultant microstructure. In comparison to the Ni/Ti compact, dehydrogenation occurring in the Ni/TiH2 compact leads to less densification, yet higher chemical homogenization, after high temperature sintering but not in the case of low temperature sintering. Moreover, there is a direct evidence of the eutectoid decomposition of NiTi at ca. 847 and 823 K for Ni/Ti and Ni/TiH2, respectively, during furnace cooling. The static and cyclic stress-strain behaviors of the porous NiTi alloys made from the Ni/Ti and Ni/TiH2 compacts were also investigated. As compared with the Ni/Ti sintered samples, the samplessintered from the Ni/TiH2 compact exhibited a much higher porosity, a higher close-to-total porosity, a larger pore size and lower tensile and compressive fracture strength.