Uniaxial Cold Compaction Research Articles

Synthesis, Consolidation and Modelling Study of AA2014-TiB<sub>2</sub> Composite Prepared by Powder Metallurgy (P/M) Method

This Aluminum alloy matrix composite reinforced with TiB2 particulates with different volume % of TiB2 (5, 10 and 15) has been successfully synthesized by P/M route. The composite powders were consolidated by cold uniaxial compaction pressure followed by sintering at 590 ̊C in nitrogen atmosphere. The effect of reinforcement on the densification was studied and reported in terms of the relative density, densification parameter, tensile rupture strength and Vickers hardness of the composite. The above physical and mechanical properties increase with compaction pressure irrespective of TiB2 content. Scheil cooling and equilibrium calculations were performed using FactSage for qualitative understanding of the microstructural evolution during sintering. The experimental results showed that samples with 5 volume % TiB2 exhibits optimum densities after sintering and correspondingly highest hardness.

An Experimental and Modeling Study of Synthesis, Consolidation and Aging Behavior of AA2014 Composite Reinforced by TiB2 via Powder Metallurgy Method

Aluminum 2014 alloy composite reinforced with TiB2 particulates with different volume% of TiB2 (5, 10 and 15%) has been successfully synthesized by P/M route. The composite powders were consolidated by cold uniaxial compaction pressure followed by sintering at 590 °C in N2 atmosphere. The Al 2014–TiB2 composites were aged at 160 °C between 0 and 8 h followed by microstructural characterization and hardness evaluation. Scheil cooling and equilibrium calculations were performed using FactSage for qualitative understanding of the microstructural evolution during sintering and aging operations. In addition, the thermo-physical properties such as hardness, density and transverse rupture strength of the sintered samples were evaluated.

A densification equation derived from the stress-deformation analysis of uniaxial cold compaction of metal powder mixes

ABSTRACTA new densification equation for uniaxial cold compaction of four low alloy steel powders was determined from the deformation vs. mean axial stress correlation. Both deformation and stress are averaged along the height of the powder column. A power law relation, with two parameters representing the plasticity and the inverse of the resistance to deformation (densification) of the powder mix, respectively, fits the curves that are divided in two steps, distinguished by the prevailingdeformation/densification mechanism (rearrangement or plastic deformation).Densification of the four powder mixes is greatly affected by the starting density in the die cavity, while the chemical composition of the base iron powder has a less significant effect.

From experimental data, the mechanics relationships describing the behaviour of four different low alloyed steel powders during uniaxial cold compaction

ABSTRACTThis work aims at determining the constitutive model of four commercial water atomised low alloyed steel powders during cold compaction. Single-action experiments were performed, obtaining cylindrical specimens with different H/D ratios. The distribution of axial and radial stresses was investigated, and the relationships describing both the radial stress transmission coefficient and the flow stress as functions of the relative density were determined. The radial stress transmission coefficient also confirmed the hypothesised value of Poisson’s coefficient. The friction coefficient between the powder column and the die wall was determined, also highlighting the influence of the H/D ratio. Measuring the axial and radial strains due to spring-back, the axial and radial elastic moduli were determined, as functions of the relative density. The results obtained for the four materials were compared, also highlighting both differences and similarities.

Microstructural Characterization of Solid State Reaction Phase Formed During Sintering of Hexagonal Boron Nitride with Iron.

In the development of dry self-lubricating composites, not only solid lubricant particle size and distribution are important, but also the correct selection of the solid lubricant characteristics, which should be stable, i.e. not reactive, during the whole processing. In this work, Fe+9 vol% h-BN composites were produced by uniaxial cold compaction and sintering, for which a reaction between h-BN and iron was detected after sintering at 1,150°C. The reaction phase was characterized by optical and scanning electron microscopy and identified by X-ray diffraction and energy-dispersive X-ray spectroscopy. The newly formed phase had high hardness when compared with the iron matrix. The resulting composites presented a high friction coefficient and high wear.

Influence of particle size distribution on nanopowder cold compaction processes

Nanopowder uniform and uniaxial cold compaction processes are simulated by 2D granular dynamics method. The interaction of particles in addition to wide-known contact laws involves the dispersion forces of attraction and possibility of interparticle solid bridges formation, which have a large importance for nanopowders. Different model systems are investigated: monosized systems with particle diameter of 10, 20 and 30 nm; bidisperse systems with different content of small (diameter is 10 nm) and large (30 nm) particles; polydisperse systems corresponding to the log-normal size distribution law with different width. Non-monotone dependence of compact density on powder content is revealed in bidisperse systems. The deviations of compact density in polydisperse systems from the density of corresponding monosized system are found to be minor, less than 1 per cent.

Effect of silver nanoparticles on the microstructure and mechanical properties of alumina ceramics

ABSTRACTIn this work, the effect of additions of silver nanoparticles on the microstructure and mechanical properties of alumina-based ceramic was studied. The processing method for the manufacturing of alumina/silver composites imply high energy mechanical milling in a planetary type mill, cold uniaxial compaction and pressureless sintering in an inert atmosphere at 1500°C for 2 h. From the results after the milling step, approximately 45% of the powders have a particle size less than 1 μm. The microstructure observed by SEM is very fine and homogenous; the presence of silver apparently inhibits the grain growth of the alumina. With respect to mechanical properties, increases of the silver content in the matrix causes decrease of Young’s modulus and flexural strength of the composite obtained in 1.5 and 4.6%, respectively. On the other hand, the presence of silver greatly enhances the fracture toughness of alumina, from an increase of 4.2 MPa m−0.5 for monolithic alumina to 10 MPa m−0.5 for alumina with silver additions of 2 wt- %, representing an improvement of 138% in toughness of alumina. Lastly, hardness for this same sample was incremented in 12%.

An Investigation on the Sinterability and the Compaction Behavior of Aluminum/Graphene Nanoplatelets (GNPs) Prepared by Powder Metallurgy

In the present study, the densification response of Al matrix reinforced with different weight percentages (0, 0.5, 1.0, 1.5 and 2.0 wt.%) of graphene nanoplatelets (GNPs) was studied. These composites were produced by a wet method followed by a conventional powder metallurgy. The Raman spectrum of graphene indicates that preparation of the composites through the wet mixing method did not affect the disordering and defect density in the GNPs structure. The nanocomposite powder mixture was consolidated via a cold uniaxial compaction. The samples were sintered at different temperatures (540, 580 and 620 °C) under nitrogen flow so as to assess the sinterability of the nanocomposites. X-ray diffraction (XRD) has been carried out to check the possible reaction between GNPs and aluminum. According to the XRD patterns, it seems that Al4C3 did not form during the fabrication process. The relative density, compressibility, sinterability and Vickers hardness of the nanocomposites were also evaluated. The effects of GNPs on the consolidation behavior of the matrix were studied using the Heckel, Panelli and Ambrosio Filho, and Ge equations. The outcomes show that at early stage of consolidation the rearrangement of particles is dominant, while by increasing the compaction pressure, due to the load partitioning effect of GNPs, the densification rate of the powder mixture decreases. Moreover, the fabricated nanocomposites exhibited high Vickers hardness of 67 HV5, which is approximately 50% higher than monolithic aluminum. The effect of graphene addition on the thermal conductivity of Al/GNPs nanocomposites was evaluated by means of thermal diffusivity measurement, and the results showed that the higher thermal conductivity can be only achieved at lower graphene content.

Microstructural Analysis and Mechanical Properties of Direct Recycling Aluminium Chips AA6061/Al Powder Fabricated by Uniaxial Cold Compaction Technique

Aluminium alloy AA6061 recycling benefits to the current and future generations by conserving energy and other natural resources. Thus with the current approach of processing technique by cold compaction technique solid state recycling made it possible for fabrication of direct recycling chips. In this research, AA6061 chips and powder were fabricated to form a sample by using uniaxial cold compaction at 9 tons for 20minutes and sintering process at temperature of 552°C. The microstructural behaviour of the recycled AA6061/Al powder samples were distributed non-homogeneously and randomly between the chips and powder region. The density of sample full chips and full powder shows the closest value to theoretical at 2.47g/cm3 and 2.43g/cm3 respectively. The hardness and compression strength examined shows the same reaction with the increasing amount of Al powder content. The full Al chips showed the highest hardness at 65.6 Hv and gradually decreased with increasing Al powder. Whereas, the maximum compression strength was at fully chip content at 307.7MPa. The compression strength decreases with increasing amount of Al powder content due to the weak bonding between the particles.

Impact of sintering method on certain properties of titanium dioxide nanopowder materials

Titanium dioxide nanopowder samples consolidated by method of cold uniaxial compaction at 200 MPa and conventionally sintered in air at 1300?? with isothermal tempering during 60 minutes or spark-plasma sintering at 1300?? and 30 MP? were studied using the method of light combination scattering spectroscopy (Raman spectroscopy) and scanning electron microscopy. The samples were found to differ significantly in terms of color, density, phase composition and microstructure.

Study of the uniaxial cold compaction of AISI 316L stainless steel powders through single action tests

The behavior during uniaxial cold compaction of a commercial mix of a water atomized austenitic stainless steel powder and a lubricant was investigated by carrying out single action tests and recording the force applied by the upper punch to the powder column, the force applied to the die, and the displacements of the crosshead and of the die. Data collected during the experiments were elaborated using different correlations between the axial stress and the radial stress in the powder column: the Poisson correlation for the elastic deformation of the powder column, and the Von Mises criterion for plastic deformation.Friction coefficient decreases on increasing relative density up to ρr=0.7, then it stabilizes on 0.15. The flow stress of the powder mix increases with the relative density by a power law. The radial stress transmission coefficient increases with relative density, with two distinct trends in the ranges where either elastic or plastic deformation of the powder column predominate.

Key parameters for spark plasma sintering of wet-precipitated iodate-substituted hydroxyapatite

A possible strategy for the management of radioactive iodine-129 is to incorporate it under the form of iodate in hydroxyapatite matrices (HA-CaI) intended to be stored in deep geological repositories. To meet disposal requirements, powder materials that were here obtained by a wet-precipitation route required shaping. In this work, we demonstrate that sintering of HA-CaI could be achieved by spark plasma sintering (SPS) at low temperature (T <300°C) without iodine volatilization. Such densification was only possible if a non apatitic hydrated calcium phosphate layer was present at the surface of grains, the content of which directly depended on synthesis conditions. The higher the proportion of hydrated layer, the better uniaxial cold compaction and densification during sintering. For an optimised HA-CaI powder, a relative density of 88% could be reached using a pressure of 100MPa, a dwell temperature of 250°C and a heating rate of 30°Cmin−1.

Densification and deformation during uniaxial cold compaction of stainless steel powder with different particle size

The behaviour of austenitic stainless steel powder column during uniaxial cold compaction was investigated in this work. Powders with different particle size were compacted to the same green density in a hydraulic press, also providing different H/D ratios in order to account for the influence of geometry. The analysis of the data continuously recorded by the press allowed distinguishing the contribution of the reversible phenomena (elastic deformation of powders and tools) and of the irreversible phenomena (rearrangement and plastic deformation of the powders). An analytical model for densification was proposed, considering both density and increase in density versus the applied pressure. The trend of reversible and permanent deformations versus the applied pressure was evaluated, also proposing an analytical model. The comparison between the densification curves and the curves of permanent deformation allowed highlighting the physical meaning of the model describing the increase in density for the different particle size.

The Influence of the Foaming Agents on the Porosity of the PM Hydroxyapatite-Based Biocomposites Processed by Two-Step Sintering

This paper presents a comparative analysis of the foaming process developed in hydroxyapatite (HAp)-based bicomposites as a function of the foaming agent. The matrix of the biocomposite consists of either submicronic or micronic powder particles of HAp. The titanium hydride powder was added as reinforcement’s precursor as well as blowing agent, and in order to increase the biocomposites’ porosity calcium carbonate was added as space holder agent. The powders mixture was homogenized in a planetary ball mill with a single grinding bowl for 1 minute in air. Uniaxial cold compaction at 120-170 MPa was performed in order to obtain cylindrical green parts, which next were heated in argon atmosphere using the two step sintering technique at temperatures of 900 °C for 1 minute and 800°C for 450 - 600 minutes. The porosity of the biocomposite is analysed through calculations and SEM and EDS analysis highlighting the influence of the above mentioned foaming techniques (blowing and space holder).

The Anisotropy of Dimensional Change on Sintering of Iron

The anisotropy of dimensional change on the sintering of iron was investigated by dilatometry. Dimensional changes are different along the longitudinal and transversal directions, and shrinkage is more pronounced parallel to the compaction direction. This phenomenon is particularly pronounced during the early stage of sintering, in the alpha field below the Curie temperature. The results were elaborated according to the kinetics model for shrinkage to calculate an effective diffusion coefficient along the two directions. Such an effective diffusion coefficient is higher parallel to the compaction direction than perpendicular to it, and both are larger than the diffusion coefficient calculated on the basis of the activation energy reported in the literature for pure iron. This discrepancy is attributed to the defectiveness introduced by cold compaction in the particle contact regions, which may enhance diffusivity owing to the dislocation pipe mechanism, which, in turn, is particularly intense below the Curie temperature. This interpretation may also justify anisotropy of shrinkage because the powder particles are inhomogeneously deformed by uniaxial cold compaction. The enhanced diffusion coefficient increases with time and shows a maximum at temperatures below the Curie point. This trend was discussed with reference to the self‐activated sintering mechanism.

Analysis of the Cold Compaction Behavior of Titanium Powders: A Comprehensive Inter-model Comparison Study of Compaction Equations

A brief background to compaction equations and their application to titanium powder is presented. The behavior and mechanisms of densification in selected titanium powders is critically analyzed by means of a comprehensive inter-model comparison of existing compaction equations. The results are discussed in terms of the comparative evaluation of cold uniaxial compaction tests of sponge Ti, CP TiH2, CP Grade 2 Ti, and TiH2-SS316L nanocomposite powder samples, which were conducted at applied compaction pressures of up to 1250 MPa.

Preparation of Molybdenum High Speed Tool Steels with Addition of Niobium Carbide by Powder Metallurgy Techniques

High speed steels processed by Powder Metallurgy (PM) techniques present better mechanical properties when compared with similar steels obtained by the conventional process of cast to ingot and hot working. PM techniques produce improved microstructures with smaller and better distribution of carbides. Liquid phase sintering high speed steel seems to be a cheaper processing route in the manufacturing of tool steels if compared to the well-known and expansive hot isostatic pressing high speed steels. The introduction of niobium as alloying element began with the object of replacing elements like vanadium (V) and tungsten (W). Phase liquid sintering consists in a manufacturing technique to process high speed steels by powder metallurgy. The aim of this work of research is to process and obtain AISI M2 and M3:2 with and without the addition of niobium carbide by high energy milling, cold uniaxial compaction and vacuum sintering in the presence of a liquid phase. The powders of the AISI M2 and M3:2 were processed by high energy milling adding a small quantity of niobium carbide (6% in mass), then the powders were characterized by means of X-ray diffraction (XRD) and scanning electron Microscopy (SEM) plus energy dispersion spectroscopy (EDS) in order to evaluate the milling process. The powders of the AISI M2 and M3:2 with the addition of niobium carbide (NbC) were uniaxially cold compacted and then submitted to vacuum sintering. The sintered samples had their microstructure, porosity and carbide distribution observed and evaluated by means of Scanning Electron Microscopy (SEM) and the mechanical property of hardness was investigated by means of Vickers hardness tests. At least five samples of each steel were investigated.

Effect of coarse grain matrix content on the mechanical behavior of trimodaled AA 6061-TiO2 nanocomposite prepared by mechanical alloying

In the present work, nanocrystalline AA 6061 alloy powders reinforced with fine titania particles were mechanically blended with coarse-grain AA 6061 alloy powders to produce a trimodal microstructure. The nanocrystallite and trimodaled composite powders were consolidated by cold uniaxial compaction, followed by sintering under controlled atmosphere. The microstructural features for the developed trimodaled composite were evaluated using an optical microscope, a scanning electron microscope, and a transmission electron microscope. The mechanical behavior of these consolidates were evaluated at room temperature. It was observed that trimodal bulk nanocomposite had exhibited balanced mechanical properties of enhanced yield strength and improved ductility compared to nanocrystallite composite.

Synthesis of Al7075 Alloy/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Composite and Corrosion Study

Al7075alloy and Al2O3 powders were synthesized via high-energy ball mill for 5 h. Al7075alloy powders were mixed with Al2O3 ranging from 5 to 15 vol. %, compacted by cold uniaxial compaction at 400 MPa. The green pellets were degassed at 350 oC for 30 min, and then sintered in the temperature of 600 oC under argon atmosphere for 120 min. It was shown that better density, vickers micro hardness and corrosion resistance were achieved up to 10 vol. % due to uniform distribution of Al2O3 particles throughout matrix. Beyond 10 vol. %, Al2O3 resulted in clustering, porosity and poor interfacial bonding and their properties.

Synthesis and Characterization of Al7075, Al7075-10 Vol. % Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Composite Prepared by High-Energy Ball Milling

Al7075 and Al2O3 powders were synthesized via high-energy ball mill for 15 h. Al7075 powders were mixed with 10 vol. % Al2O3, compacted by cold uniaxial compaction at 400 MPa. The green pellets were degassed at 350 oC for 30 min, and then sintered in the temperature of 600 oC under argon atmosphere for 120 min. It was shown that better density, vickers micro hardness and corrosion resistance were achieved due to refinement of grain size. HRTEM micrographs demonstrated a uniform distribution of Al2O3 particles in aluminium alloy and equilibrium η (MgZn2) precipitates along the grain boundaries.