Multicomponent Powders Research Articles

Selective Laser Melting of Multi-Component Ni-Based Powder Mixture for Building Metallic Parts

Selective laser melting (SLM) is an advanced manufacturing technology, which is flexible in building three-dimensional (3D) metallic parts. In this work, SLM experiment of a multicomponent Ni-based composite powder, which consisted of Ni, Cr, Fe, and Al powders, was conducted with favorable forming ability. The SEM, EDX, and XRD analysis were used to characterize the surface morphology, microstructure, and phase structure of as-formed Ni-based alloy. The XRD analysis showed that the as-received phase structure was Ni based solid solution. The SEM analysis of surface morphology revealed that metal agglomerates or balls were very easily formed in SLM surface, between which some pore channels existed. The surface condition and porosity could be improved by increasing laser energy input, because of a higher molten temperature and accordingly better flowing and flatting characteristics. The SEM analysis of microstructure showed that the crystalline grains were in cellular and columnar shape. Moreover, the grains were very fine with average dimensions about 5μm, due to the rapid cooling rate with rapid laser beam moving. The EDX analysis illustrated that the element contents of starting powder were uniformly distributed in as-prepared sample. A case investigation into SLM of this composite powder to form an impeller was also performed.

Analysis of Powder Caking in Multicomponent Powders Using Atomic Force Microscopy to Examine Particle Properties

AbstractAtomic force microscopy has been used to study the surface properties of model spray dried powders. Phase imaging, nanoindentation and force modulation microscopy have differentiated between the different surface material properties of the particles, revealing a regular dispersion of soft, oil rich areas distributed across the particles' surface. Humidity and temperature cycling effects on the caking behavior of the particles have also been investigated, with significant morphology changes and onset of caking found to occur within relatively short periods of time.

Preparation and Selective Laser Sintering Mechanism of Polymer-Coated Mo Powder

A multi-component polymer-coated molybdenum powder was chosen for selective laser sintering (SLS). A novel preparing method of polymer-coated molybdenum powder was presented. The effect of the process parameters on the part’s characteristics is investigated. Based on our study for dynamic laser sintering process of polymer-coated molybdenum powder, its laser sintering mechanism was reported as follows: at the early stage of laser sintering, the viscous flow is the major mechanism; during the laser sintering, the melting/solidification is the major mechanism. Furthermore, a model corresponding to the mechanism was discussed schematically, which could be used to explain the material migrating mode during laser sintering process.

Numerical Simulation of Multi-Component Powder in Selective Laser Sintering

The process of sintering material from the powder to the liquid with high temperature and then to the continuous solid are simulated, considering the effects of heat conduction, thermal radiation, thermal convection and thermal physical parameters on temperature. The results show that the temperature gradient is larger in the front of pool, and the end of which is smaller due to the fast-moving laser beam and uneven distribution of laser energy. With the increase of scanning time, the overall temperature of substrate and powder particles is gradually rising, the heat-affected zone is increasing and the asymmetric temperature distribution has become more obvious for the heat conduction. As the pool depth is larger than the powder thickness and the pool width is larger than the scanning spacing at the current process parameters, the bond strength of layers and scanning lines is enough.

Calibration sampling paradox in near infrared spectroscopy: A case study of multi-component powder blend

The objective of this study was to illustrate the sampling paradox resulting from the different strategies of spectral acquisition while preparing and implementing the calibration models for prediction of blend components in multi-component cohesive blends. A D-optimal mixture design was used to create 24 blending runs of the formulation consisting of chlorpheniramine maleate, lactose, microcrystalline cellulose and magnesium stearate. Three strategies: (a) laboratory mixing and static spectral acquisition, (b) IBC mixing and static spectral acquisition and (c) IBC mixing and dynamic spectral acquisition were investigated for obtaining the most relevant and representative calibration samples. An optical head comprising a sapphire window mounted on the lid of the IBC was used for static and dynamic NIR spectral acquisition of the powder blends. For laboratory mixed samples, powders were blended for fixed period of 30 min and later on scanned for NIR spectra. For IBC mixed blends, the spectral acquisition was carried out in-line for 2 min and stopped for static spectral acquisition. The same cycle was repeated for the next 28 min. Partial least square (PLS) calibration models for each component were built and ranked according to their calibration statistics. Optimal calibration models were selected from each strategy for each component and used for in-line prediction of blend components of three independent test runs. Although excellent statistics were obtained for the PLS models from the three strategies, significant discrepancies were observed during prediction of the independent blends in real time. Models built using IBC mixed blends and dynamic spectral acquisition resulted in the most accurate predictions for all the blend components, whereas models prepared using static spectral acquisition (laboratory mixed and IBC) showed erroneous prediction results. The prediction performance differences between the models obtained using the different strategies could be explained in the context of relevancy and representative sample collection at the initial stage of calibration model building.

In-line quantification of drug and excipients in cohesive powder blends by near infrared spectroscopy

This work was aimed at investigating the utility of near infrared (NIR) spectroscopy for simultaneous in-line quantification of drug and excipients in cohesive powder blends in a bin blender. A model formulation containing micronized chlorpheniramine maleate (μCPM), lactose, microcrystalline cellulose (MCC) and magnesium stearate (MgSt) was selected for the blending study. An optical head comprising a sapphire window mounted on the lid of the bin was used to collect in-line NIR spectral data of the powder blends. Validated partial least square (PLS) calibration models were used to quantify each component from the NIR spectra of the blends. Additionally, effects of premixing by sieving and high shear mixing and use of an internal prism fixed within the bin on the mixing performance of each component were studied. The statistical results obtained for PLS calibration models and their validation showed the sensitivity of NIR for accurate quantification of blend components. The blend prepared with high shear premixing and with prism achieved uniformity more rapidly than that with high shear premixing but without prism during blending in a bin blender. Premixing using sieving proved to be inadequate for uniform mixing of the blend components as none of the components except MgSt achieved uniform distribution after the preset blending time when blended in the bin blender. This study demonstrated that by high speed sampling and rapid spectral acquisition, distribution of individual blend components can be assessed with high accuracy during blending. Furthermore, high shear premixing facilitated rapid distribution and uniformity achievement of blend components. This technique may be used to monitor the relative distribution of individual blend components in real time and thus, to assess the performance of a bin blender for mixing of cohesive multi-component powder blends during development and production.

Description of the dependence of intensity of x-ray fluorescence on the particle size of powder samples and pulp during x-ray fluorescent analysis

The dependence of intensity of x-ray fluorescence on particle size for powdered and pulplike media is described using a general analytical expression. The expression is obtained for a model of a powder medium consisting of particles of various sizes distributed randomly in the sample bulk. This expression involves expressions for the fluorescence intensity for homogeneous and pulplike media as limiting cases. The results of calculations by these expressions agree satisfactorily with the literature and experimental data for binary powder mixtures. The model allows one to evaluate the effect of the particle size of the powder on the fluorescence intensity for a multicomponent polydispersed powder medium.

Development of synthetic technology of multicomponent oxide powder materials and ferroelectric ceramics on their basis

The synthetic method of ultrafine multicomponent oxide powders of the composition of special-purity grade Pb(Sc0.5−xNb0.5Rx)O3 is developed. Optimal modes for obtaining a stable hydroxy polymer based on lead scandate-niobate in the form of a bound dispersed colloid system and the modes of its thermal treatment for obtaining stoichiometric powders with specific properties are established. The possibilities of optimizing the properties and fabrication technology of electrooptical ceramics via the introduction of modifying additives are considered.

Effect of fat content on the dissolution enthalpy and kinetics of a model food powder

The enthalpy of dissolution of a model food powder containing increasing amount of fat was studied by means of isothermal solution calorimetry. The samples were characterized utilizing scanning electron microscopy (SEM), near infrared reflectance (NIR), and X-ray powder diffraction (XRPD). The water and fat content, specific surface area and density of the samples were also determined. Conductivity measurements were utilized to quantify the dissolution kinetics of the samples. All the samples showed an exothermic dissolution behavior, due to the amorphous state of their main components. The exothermic response decreased linearly as the fat content of the samples increased, possibly due to the reduced amount of amorphous material present in the samples. The dissolution rate was significantly affected by the amount of fat in the powder. The enthalpy of dissolution of a multi-component powder could be predicted from the additive enthalpy measured from its single components. The enthalpy of dissolution provides new and valuable information to better characterize the dissolution process of food powders.

Far-from-Equilibrium Processing of Multiphase Ceramic Nanocomposites

A new far-from-equilibrium processing methodology has been developed to produce multiphase nanocomposite ceramics. The proposed method uses the following steps: (a) spray drying of commercially available powders to make flowable multicomponent feed powder aggregates, (b) plasma melting and quenching to generate dense and homogeneous metastable powders, and (c) pressure assisted consolidation of these powders to make dense nanocomposite ceramics. By controlling of process parameters, inherent superplasticity of these powders can be used to aid in densification process. In this article, results on multiphase zirconia- and alumina-based ceramics will be presented.

Fabrication of Nano-Sized Titanate Powders by an Ethylene Glycol Solution Route

Several titanate powders (Al2TiO5, SrTiO3, etc.) were synthesized by an ethylene glycol solution route. Titanium isopropoxide and nitrate salts were dissolved in stoichiometric proportions in liquid-type ethylene glycol without any precipitation. The parent precursor sols were dried to porous gels, and then the gels were calcined and crystallized. All synthesized titanate powders had stable crystallization behavior at low temperature and high specific surface area after a simple ball-milling process. A three-component PZT (Pb(Zr0.52·Ti0.48)O3) powder was also synthesized successfully by the ethylene glycol method. In this study, the characteristics of the multi-component titanate powders by the ethylene glycol method are examined.

Numerical Simulation and Forecasting of Mechanical Properties for Multi-Component Nonferrous Dispersion-Hardened Powder Materials

A new mathematical simulation technique for physico-mechanical properties of multicomponent powder materials is proposed in this paper. The main advantage of the technique is that finite elements representing different components are placed into a common mesh and may exchange their properties. The input data are properties of components and specified value of porosity. The output data are properties of material after sintering. The technique allows us to investigate the influence of each component of a material on the properties and distribution of properties inside the sample. The comparative analysis of materials with different compositions is based on simulation results that are well concordant with the results of the laboratory experiments.

Si–C–N–Fe nanostuctured ceramics from inorganic polymer precursors obtained by plasma polymerization

Multicomponent powders based on SiCN and SiCN containing iron systems are of great interest as starting materials for sintering advanced ceramics and composites with improved properties for high temperature applications.We report a versatile method by which are designed inorganic polymers with a defined composition as precursors for a ceramic with induced properties. The synthesis of Si–C–N and Si–C–N–iron polymer precursors are performed in improved configuration of plasma assisted chemical vapor deposition (CVD) coupled with chemical transport reaction (CTR) with inorganic monomers, hexamethyldisilazane and ferrocene/hexamethyldisilazane as precursors. Further, the resulted polymers are then pyrolysed at 1200 °C under nitrogen atmosphere into nanostructured ceramics (such as Si3N4, Fe3C).The conversion process of the polymer precursors into a nanostructured ceramic was followed mainly by FTIR, XRD, TEM and SEM investigation. Infrared spectroscopy of polymers revealed the presence of Si–C, Si–N, C–N and hydrogenated bonds. Transmission electron microscopy showed that the polymers are made of nanometric round-shape particles with the average particle size around 20–40 nm for SiCN and 40–80 nm for SiCN containing iron.

Predicting the Tensile Strength of Compacted Multi-Component Mixtures of Pharmaceutical Powders

Pharmaceutical tablets are generally produced by compacting a mixture of several ingredients, including active drugs and excipients. It is of practical importance if the properties of such tablets can be predicted on the basis of the ones for constituent components. The purpose of this work is to develop a theoretical model which can predict the tensile strength of compacted multi-component pharmaceutical mixtures. The model was derived on the basis of the Ryshkewitch-Duckworth equation that was originally proposed for porous materials. The required input parameters for the model are the relative density or solid fraction (ratio of the volume of solid materials to the total volume of the tablets) of the multi-component tablets and parameters associated with the constituent single-component powders, which are readily accessible. The tensile strength of tablets made of various powder blends at different relative density was also measured using diametrical compression. It has been shown that the tensile strength of the multi-component powder compacts is primarily a function of the solid fraction. Excellent agreement between prediction and experimental data for tablets of binary, ternary and four-component blends of some widely used pharmaceutical excipients was obtained. It has been demonstrated that the proposed model can well predict the tensile strength of multi-component pharmaceutical tablets. Thus, the model will be a useful design tool for formulation engineers in the pharmaceutical industry.

MICROSTRUCTURE DEVELOPING MECHANISM IN SELECTIVE LASER SINTERING OF MULTI-COMPONENT Cu-BASED ALLOY POWDER

Selective laser sintering of a multi-component Cu-based metal powder with the Cu, CuSn and CuP weight ratio of 55 : 35 : 10 has been successfully processed. The CuSn metal powder with a lower melting point acts as the binder, while the Cu powder with a higher melting point acts as the structural metal. The CuP powder is taken as a fluxing agent to improve the wetting characteristics. The dominant sintering mechanism is liquid formation and particle rearrangement. Care should be taken to determine the suitable processing parameters (laser power of 275~400 W and scan speed of 0.03 ~ 0.06 m·s-1) in order to ensure the melting of the binder CuSn but the non-melting of the structural metal Cu. Under condition that the mechanism of liquid phase sintering with partial melting of the powder prevails, increasing laser power or decreasing scan speed can generally improve sintering density and structural homogeneity.

Atomization of metal fluorides for enhanced flow characteristics of a multicomponent powder

The National Aeronautics and Space Administration's (NASA's) PS304 coating is a plasma spray deposited tribological coating with feedstock composed of NiCr, Cr 2O 3, Ag and BaF 2–CaF 2 powders. The effects of rounded BaF 2–CaF 2 particles on the gravity-fed flow characteristics of PS304 feedstock have been investigated. The BaF 2–CaF 2 powder was fabricated by water atomization using four sets of process parameters. Each of these powders was then characterized by microscopy and classified by screening to obtain 45–106 μm particles and added incrementally from 0–10 wt.% to the other constituents of the PS304 feedstock, namely nichrome, chromia and silver powders. The relationship between feedstock flow rate, measured with the Hall flowmeter, and concentration of fluorides was found to be linear in each case. The slopes of the lines were between those of the linear relationships previously reported using angular and spherical fluorides and were closer to the relationship predicted using the rule of mixtures. The results offer a fluoride fabrication technique potentially more cost-effective than gas atomization processes or traditional comminution processes.

Thermal transitions in Fe–Ti–Cr–C quaternary system used as precursor during laser in situ carbide coating

The temperature range of thermal transitions within the quaternary system (Fe, Ti, Cr, and C) and the thermal stability of the evolved phases were studied with the help of differential scanning calorimetry (DSC). DSC studies indicated that the major exothermic reactions (formation of carbides) take place within 850–1150 °C. The evolved phases (TiC, M 7C 3, Fe–Cr, and Fe 3C) were characterized using X-ray diffraction (XRD). This multicomponent powder mixture was used as a precursor for synthesizing a composite coating on the surface of steel via laser surface engineering (LSE). The intended wear applications of the coating made thermal stability investigations vital. Experimental evaluation of thermal stability of the phases formed was done.

Characteristics and Applications of Nanostructured Nitrides Synthesized by Vapor Phase Reactions

AbstractGas phase ammonolysis of volatile metal chlorides at elevated temperatures is a favorable way to produce nitride or oxynitride nanopowders. Their composition as well as the physico-chemical properties is determined by reaction temperature, molar ratio of the reactants and the residence time of the gases in the reaction zone. Both single and multi component powders can be obtained. Typical particle sizes are in the range of 50 to 350 nm. The specific surface can reach values up to 300 m2/g. Microporous analysis revealed the presence of pores with a diameter between 0.6 and 0.7 nm in amorphous silicon nitride. The powders can be used, depending on the characteristics, as catalyst or basic catalyst support. The paper gives an overview about vapor phase synthesis of single and multi component nitrides as well as the use of amorphous silicon nitride as a basic catalyst support for dehydrogenation of propane.

Application of the Genetic Algorithm Joint with the Powell Method to Nonlinear Least-Squares Fitting of Powder EPR Spectra

The application of the stochastic genetic algorithm (GA) in conjunction with the deterministic Powell search to analysis of the multicomponent powder EPR spectra based on computer simulation is described. This approach allows for automated extraction of the magnetic parameters and relative abundances of the component signals, from the nonlinear least-squares fitting of experimental spectra, with minimum outside intervention. The efficiency and robustness of GA alone and its hybrid variant with the Powell method was demonstrated using complex simulated and real EPR data sets. The unique capacity of the genetic algorithm for locating global minima, subsequently refined by the Powell method, allowed for successful fitting of the spectra. The influence of the population size, mutation, and crossover rates on the performance of GA was also investigated.

Joint-probability methods for indexing impure and multi-component powder diffraction patterns

Joint-probability methods for indexing impure and multi-component powder diffraction patterns