Powder Gas Research Articles

Process Evaluation of AISI 4340 Steel Manufactured by Laser Powder Bed Fusion

Laser powder bed fusion (L-PBF) involves the consolidation of metal powder, layer by layer, through laser melting and solidification. In this study, process parameters are optimized for AISI 4340 steel to produce dense and homogeneous structures. The optimized process parameters produce mechanical properties at the center of the build plate that are comparable to wrought in the vertical and horizontal orientations after heat treatment and machining. Four subsequent builds are filled with specimens to evaluate the mechanical behavior as a function of location and orientation. Variations in the mechanical properties are likely due to recoater blade interactions with the powder and uneven gas flow. The results obtained in this study are analyzed to assess the reliability and reproducibility of the process. A different build evaluates the performance of near-net-shaped tensile specimens angled 35°-90° from the build plate surface (horizontal). Ductility measurements and surface roughness vary significantly as a function of the build angle. In the stress-relieved and as-built conditions, the mechanical behavior of vertically oriented specimens exhibits somewhat lower and more variable ductility than horizontally oriented specimens. Therefore, several process variables affect the mechanical properties of parts produced by the L-PBF process.

Measurement correction method for force sensor used in dynamic pressure calibration based on artificial neural network optimized by genetic algorithm

We present an optimization algorithm to obtain low-uncertainty dynamic pressure measurements from a force-transducer-based device. In this paper, the advantages and disadvantages of the methods that are commonly used to measure the propellant powder gas pressure, the applicable scope of dynamic pressure calibration devices, and the shortcomings of the traditional comparison calibration method based on the drop-weight device are firstly analysed in detail. Then, a dynamic calibration method for measuring pressure using a force sensor based on a drop-weight device is introduced. This method can effectively save time when many pressure sensors are calibrated simultaneously and extend the life of expensive reference sensors. However, the force sensor is installed between the drop-weight and the hammerhead by transition pieces through the connection mode of bolt fastening, which causes adverse effects such as additional pretightening and inertia forces. To solve these effects, the influence mechanisms of the pretightening force, the inertia force and other influence factors on the force measurement are theoretically analysed. Then a measurement correction method for the force measurement is proposed based on an artificial neural network optimized by a genetic algorithm. The training and testing data sets are obtained from calibration tests, and the selection criteria for the key parameters of the correction model is discussed. The evaluation results for the test data show that the correction model can effectively improve the force measurement accuracy of the force sensor. Compared with the traditional high-accuracy comparison calibration method, the percentage difference of the impact-force-based measurement is less than 0.6% and the relative uncertainty of the corrected force value is 1.95%, which can meet the requirements of engineering applications.

Low temperature synthesis of uranium mononitride powder

The uranium mononitride (UN) powder was successfully synthesized through the quantitative nitridation between uranium powder and nitrogen gas at 873 K in this work. After quantitative nitridation at 873 K for 16 h, the single phase of UN powder could be obtained. The realization of the low-temperature synthesis of UN was attributed to the solid-phase reaction between uranium sesquinitride and uranium. The reaction product was mainly UN after calcining the mixture of uranium sesquinitride and uranium powder at 873 K for 8 h, for the Gibbs free energy of this reaction at the 873 K was −160.91 kJ/mol.

Effects of process parameters on properties of porous foams formed by laser-assisted melting of steel powder (AISI P21)/foaming agent (ZrH2) mixture

This paper describes the fabrication of lightweight metal foams using the directed energy deposition (DED) method. DED is a highly flexible additive manufacturing process wherein a metal powder mixed with a foaming agent is sprayed while a high-power laser is used to simultaneously melt the powder mixture into layered metal foams. In this study, a mixture of a carbon steel material (P21 powder) and a widely used foaming agent, ZrH2, is used to fabricate metal foams. The effects of various process parameters, such as the laser power, powder feed rate, powder gas flow rate, and scanning speed, on the deposition characteristics (porosity, pore size, and pore distribution) are investigated. The synthesized metal foams exhibit porosities of 10% or lower, and a mean pore area of 7×105μm2. It is observed that the degree of foaming increases in proportion to the laser power to a certain extent. The results also show that the powder feed rate has the most pronounced effect on the porosity of the metal foams, while the powder gas flow rate is the most suitable parameter for adjusting the size of the pores formed within the foams. Further, the scanning speed, which determines the amounts of energy and powder delivered, has a significant effect on the height of the deposits as well as on the properties of the foams. Thus, during the DED process for fabricating metal foams, the pore size and distribution and hence the foam porosity can be tailored by varying the individual process parameters. These findings should be useful as reference data for the design of processes for fabricating porous metallic materials that meet the specific requirements for specialized parts.

Structural and mechanical properties of CVD deposited titanium aluminium nitride (TiAlN) thin films

Titanium aluminium nitride (TiAlN) thin films were deposited by chemical vapour deposition using TiO2 powder, Al powder and N2 gas. The morphology and mechanical properties of the films were characterized by scanning electron microscopy and nanoindentation technique, respectively. The structural properties were characterized by Raman spectroscopy and X-ray diffraction. The XRD result shows TiAlN films are of NaCl-type metal nitride structure. Micro-Raman peaks of the TiAlN thin film were observed within 450 and 642 cm−1 for acoustic and optic range, respectively. A maximum hardness and Young modulus up to 22 and 272.15 GPa, respectively, were observed in the TiAlN film deposited at 1200 °C.

Analysis of track formation during laser metal deposition

A fundamental understanding of the physical phenomena associated with the coaxial laser metal deposition (LMD) process is essential to enhance the science base and thereby improve the process itself. The interaction between the laser beam and the powder particles leads to an attenuation of the beam intensity and to a temperature rise of the powder particles before reaching the melt pool. To understand this mutual influence and their influence on the process result better, the powder gas stream was analyzed with an image-based particle density measurement system. This system illuminates the powder gas stream from the side with a line laser light source and monitors the particles plane by plane with a coaxially aligned camera through the powder nozzle. A high image rate allows to record the number and position of individual powder particles. The particle density distributions in the planes are determined by averaging over the images. With this, a statistical model can be derived with regard to the particles trajectories. Finally, with these results it is possible to analyze the shadowing of the laser beam by the powder particles and the change of the particle temperature in detail. The transmitted laser intensity distribution and mean particle temperature are used as boundary conditions for the governing equations of the mathematical model for the real LMD process. LMD represents mathematically a free boundary value problem. This means that the track geometry is part of the solution. The mathematical model is based on an integration of the time dependent heat equation and the computation of the track geometry with the nonlinear Young-Laplace equation, whereby a mass balance with regard to the particles which reach the melt pool surface is taken into account. The governing equations are solved with the Finite Element Method and the moving mesh approach is used in order to implement a track adapted meshing. The results concerning the track geometry show excellent agreement with the experimental ones which are determined by cross sections of laser material deposited tracks and images from high speed videography. The model does not use any geometrical approximation of the melt pool surface but determines the melt pool surface shape by the balance equation for capillary forces and mass balance.

Effect of addition of micron-sized TiC particles on mechanical properties of Si3N4 matrix composites

Abstract The effect of micron-sized TiC particles on mechanical properties of Si 3 N 4 matrix composites was investigated. Si 3 N 4 TiC composites were fabricated by using powder metallurgy and gas pressure sintering (GPS) methods. In order to achieve high mechanical properties, the experimental data were carried out with five different Si 3 N 4 TiC contents. Hardness, fracture toughness and relative density of Si 3 N 4 TiC composites were characterized. The result indicated that the highest relative density (98.0%) and fracture toughness (K IC = 8.4 MPa m 1/2 ) were measured for monolithic silicon nitride and 5 wt% TiC, respectively. Qualitative and quantitative phase compositions were analyzed by X-ray diffraction (XRD). The experimental analyses indicated that the TiC phase reacted with Si 3 N 4 during the liquid phase sintering, resulting in formation of TiC 0.3 N 0.7 . The phase transition, crystal growth, microstructure and mechanical properties of composites were investigated by scanning electron microscopy (SEM). Due to the inhibition of the grain growth, the aspect ratio exhibited a higher value from SNT0 (aspect ratio = 4.54) to SNT5 (aspect ratio = 5.60). The toughening mechanism of Si 3 N 4 TiC composites was attributed to crack deflection and crack impedance by periodic compressive stress in the Si 3 N 4 matrix. However, the increase of the TiC content easily led to excessive connection microcrack, which would not be beneficial for the strength.

Scanning Speed Influence on the Microstructure and Micro hardness Properties of Titanium Alloy Produced by Laser Metal Deposition Process

Ti6Al4V is an important automobile and aerospace alloy because of its excellent properties, but it is challenging to process this material through the conventional manufacturing processes. Laser metal deposition process which is an additive manufacturing technologies an alternative manufacturing process that offers lots of advantages for processing difficult to manufacture materials like titanium and its alloys. Laser metal deposition process has the ability to improve the properties of materials and also improve the fuel efficiency of moving parts by making them lighter and hence help to reduce the carbon foot printing in the transportation industry. Laser metal deposition process (LMD) is fairly new and some of the process physics still needs to be understood. In this study, the effect of scanning speed on the resulting metallurgical and mechanical properties of Ti6Al4V powder deposited using LMD was studied. Ti6Al4V powder was deposited coaxially with a 4.0 Kw Rofin Sinar Nd: YAG laser on Ti6Al4V substrate. The laser power, powder flow rate and gas flow rate were kept constant while the scanning speed was varied between 0.005 and 0.095m/sec. The microstructures of the samples were studied using the optical microscope and the micro hardness was also measured using the Vickers hardness tester. The properties of the deposited samples were studied with the varying scanning speed.The micro hardness was found to increase with the increase in the scanning speed

CFA-4 - a fluorinated metal-organic framework with exchangeable interchannel cations.

The syntheses and crystal structures of the fluorinated linker 1,4-bis(3,5-bis(trifluoromethyl)-1H-pyrazole-4-yl)benzene (H2-tfpb; 1) and the novel metal-organic framework family M[CFA-4] (Coordination Framework Augsburg University-4), M[Cu5(tfpb)3] (M = Cu(i), K, Cs, Ca(0.5)), are described. The ligand 1 is fully characterized by single crystal X-ray diffraction, photoluminescence-, NMR-, IR spectroscopy, and mass spectrometry. The copper(i)-containing MOF crystallizes in the hexagonal crystal system within the chiral space group P6322 (no. 182) and the unit cell parameters are as follows: a = 23.630(5) Å, c = 41.390(5) Å, V = 20 015(6) Å3. M[CFA-4] features a porous 3-D structure constructed from pentanuclear copper(i) secondary building units {Cu(pz)6}- (pz = pyrazolate). Cu(I)[CFA-4] is fully characterized by synchrotron single crystal X-ray diffraction, thermogravimetric analysis, variable temperature powder X-ray diffraction, IR spectroscopy, photoluminescence and gas sorption measurements. Moreover, thermal stability and gas sorption properties of K[CFA-4] and Cu(I)[CFA-4] are compared.

Pressure prediction model based on artificial neural network optimized by genetic algorithm and its application in quasi-static calibration of piezoelectric high-pressure sensor.

This paper applies back propagation neural network (BPNN) optimized by genetic algorithm (GA) for the prediction of pressure generated by a drop-weight device and the quasi-static calibration of piezoelectric high-pressure sensors for the measurement of propellant powder gas pressure. The method can effectively overcome the slow convergence and local minimum problems of BPNN. Based on test data of quasi-static comparison calibration method, a mathematical model between each parameter of drop-weight device and peak pressure and pulse width was established, through which the practical quasi-static calibration without continuously using expensive reference sensors could be realized. Compared with multiple linear regression method, the GA-BPNN model has higher prediction accuracy and stability. The percentages of prediction error of peak pressure and pulse width are less than 0.7% and 0.3%, respectively.

Using Modern Solid-State Analytical Tools for Investigations of an Advanced Carbon Capture Material: Experiments for the Inorganic Chemistry Laboratory

A simple and straightforward synthesis of an ultrastable porous metal–organic framework (MOF) based on copper(II) and a mixed N donor ligand system is described as a laboratory experiment for chemistry undergraduate students. These experiments and the resulting analysis are designed to teach students basic research tools and procedures while emphasizing one of the most challenging environmental issues we are facing as a society: reduction of anthropogenic carbon dioxide emissions, and potential technologies that may achieve this. The described experiments take advantage of modern solid-state analytical tools, such as powder X-ray diffraction, thermogravimetric analysis, and gas sorption, to characterize the properties of this particular MOF. The adsorption studies, performed volumetrically and gravimetrically, both have simple experimental setups and enable the students to critically interpret and compare their results. Most importantly, students are required to question structure–property relationships i...

감압 순환유동층 플라즈마 반응기의 축방향 고체체류량

감압상태(1torr)의 순환유동층 플라즈마 반응기(내경 10 mm, 높이 800 mm)에서 기상 유속과 고체순환속도가 축방향 고체체류량 분포에 미치는 영향을 연구하였다. 폴리스타이렌 고분자 입자와 질소가스를 고체 및 기상 물질로 각각 사용하였다. 감압상태 순환유동층의 고체 순환량 변화는 상승관의 많은 기체 유량(40~80 sccm)에 의한 변화만큼 고체재순환부의 작은 유량 변화(6.6~9.9 sccm)에 의해서도 가능하였다. 감압상태 순환유동층의 고체 순환속도는 재순환부 기체 유속에 따라 증가하였다. 상승관내의 축방향 고체 체류량 분포는 하부의 농후상 영역에서 상부의 희박상 영역까지 높이에 따라 감소하는 형태를 나타내었다. 상승관 내 각 높이에서 고체순환속도의 증가에 따라 직선적으로 고체 체류량이 증가하였다. 이로써 플라즈마 형성과 유지 그리고 플라즈마 반응을 위해 적절한 플라즈마 로드 위치를 결정할 수 있다. The effects of gas velocity and solid circulation rate on the axial solid holdup distribution have been determined in a 10 mm-I.D. <TEX>${\times}$</TEX> 800 mm-high circulating fluidized bed plasma reactor under reduced pressure (1torr). Polystyrene polymer powder and nitrogen gas are used as solid and gas materials respectively. The change of solid circulation rate by a large gas flow rate of the riser (40~80 sccm) is also possible by a relatively small gas flow rate of the solid recirculation part (6.6~9.9 sccm). The solid circulation rate in the reactor under reduced pressure increases with increasing aeration velocity in the solid recirculation part. The axial solid holdup in the riser decreases from the dense at the bottom to the dilute phase at the top section of the riser. Solid holdups at the axial positions in the riser increase linearly with increasing solid circulating velocity. From these results, we could determine the position of plasma load for good plasma ignition, maintain and plasma reaction.

Two highly porous single-crystalline zirconium-based metal-organic frameworks

Herein we report two highly porous Zr-based metal-organic frameworks (MOFs, 1 and 2 ) constructed by the truncated octahedral secondary building unit (SBU) of Zr6O4(OH)4(CO2)12 and the organic linear ligand of 4,4ʹ-stilbenedicarboxylic acid (H2sbdc) or 4,4′-azobenezenedicarboxylic acid (H2abdc). Both Zr-based MOFs are obtained as single crystals of suitable size for single-crystal X-ray diffraction analysis. Furthermore, these two Zr-based MOFs have been fully characterized by powder X-ray diffraction (PXRD) studies, thermogravimetric analysis (TGA), infrared spectroscopy (IR) and gas adsorption analysis. In particular, their CO2 gas adsorption behaviors have been investigated and discussed.

Isostructural and cage-specific replacement occurring in sII hydrate with external CO2/N2 gas and its implications for natural gas production and CO2 storage

A replacement technique has been regarded as a promising strategy for both CH4 exploitation from gas hydrates and CO2 sequestration into deep-ocean reservoirs. Most research has been focused on replacement reactions that occur in sI hydrates due to their prevalence in natural gas hydrates. However, sII hydrates in nature have been also discovered in some regions, and the replacement mechanism in sII hydrates significantly differs from that in sI hydrates. In this study, we have intensively investigated the replacement reaction of sII (C3H8+CH4) hydrate by externally injecting CO2/N2 (50:50) gas mixture with a primary focus on powder X-ray diffraction, Raman spectroscopy, NMR spectroscopy, and gas chromatography analyses. In particular, it was firstly confirmed that there was no structural transformation during the replacement of C3H8+CH4 hydrate with CO2/N2 gas injection, indicating that sII hydrate decomposition followed by sI hydrate formation did not occur. Furthermore, the cage-specific replacement pattern of the C3H8+CH4 hydrate revealed that CH4 replacement with N2 in the small cages of sII was more significant than C3H8 replacement with CO2 in the large cages of sII. The total extent of the replacement for the C3H8+CH4 hydrate was cross-checked by NMR and GC analyses and found to be approximately 54%. Compared to the replacement for CH4 hydrate with CO2/N2 gas, the lower extent of the replacement for the C3H8+CH4 hydrate with CO2/N2 gas was attributable to the persistent presence of C3H8 in the large cages and the lower content of N2 in the feed gas. The structural sustainability and cage-specific replacement observed in the C3H8+CH4 hydrate with external CO2/N2 gas will have significant implications for suggesting target gas hydrate reservoirs and understanding the precise nature of guest exchange in gas hydrates for both safe natural gas production and long-term CO2 sequestration.

Entrainment characteristics of fine particles in fluidized bed under preheating conditions

The entrainment characteristics of fine silicon particles from solid mixtures (Geldart groups C and B) are investigated in a cylindrical fluidized bed with an inner diameter of 30mm and a height of 450mm and that is equipped with an agitator and an electromagnetic vibration table. Silicon particles (mean size of 2.7μm) are used as entrained materials (group C), hollow alumina pellets (mean size of 1200μm) are used as coarse particles (group B), and nitrogen gas is applied as carried gas. The effects of the superficial velocity of nitrogen gas at room temperature (U, 0.39m/s to 0.98m/s), the initial loading quantity of fine particles (M, 5g to 20g), the vibration intensity (Γ, 1.3 to 4.83), the stirring speed of agitator (V, 75rpm to 195rpm), the mass ratio of coarse to fine particles (N, 0 to 1.5), and the preheating temperature of nitrogen gas (T, 20°C to 170°C) on the entrainment characteristics (entrainment rate Wi and entrained powder–gas ratio R) are experimentally studied under atmospheric pressure. Significance analyses of U, M, Γ, and V are performed via the analysis of variance. M and U both significantly affect Wi, but only M significantly affects R. The experimental results show that an increase in U, M, N, and T constantly improves the entrainment characteristics, an increase in Γ deteriorates such characteristics, whereas there exists an optimal value for V to obtain the optimum entrainment characteristics. This study also determines that an optimal operating condition can result in optimal entrainment characteristics (Wi, 9.27g/min and R, 0.19g/g), which can be achieved with a U of 0.98m/s, M of 20g, Γ of 1.3, V of 155rpm, N of 1.0, and T of 170°C.

Zirconium Phosphate Supported MOF Nanoplatelets.

We report a rare example of the preparation of HKUST-1 metal-organic framework nanoplatelets through a step-by-step seeding procedure. Sodium ion exchanged zirconium phosphate, NaZrP, nanoplatelets were judiciously selected as support for layer-by-layer (LBL) assembly of Cu(II) and benzene-1,3,5-tricarboxylic acid (H3BTC) linkers. The first layer of Cu(II) is attached to the surface of zirconium phosphate through covalent interaction. The successive LBL growth of HKUST-1 film is then realized by soaking the NaZrP nanoplatelets in ethanolic solutions of cupric acetate and H3BTC, respectively. The amount of assembled HKUST-1 can be readily controlled by varying the number of growth cycles, which was characterized by powder X-ray diffraction and gas adsorption analyses. The successful construction of HKUST-1 on NaZrP was also supported by its catalytic performance for the oxidation of cyclohexene.

Material Integration for Flexible Electronics for Energy Application Using Nanoparticulated Dense and Stress-Free Ceramic Thick Film

Material Integration for Flexible Electronics for Energy Application Using Nanoparticulated Dense and Stress-Free Ceramic Thick Film

Sintering and properties of MIM M2 high speed steel produced by prealloy and master alloy routes

The advantages of powder metallurgical processing of tool steels have been recognized for many years with water atomized [1] powder being used in press & sinter valve seat parts for many years and gas atomized tool steel powders consolidated by HIP used in high performance applications [2] . While coarse HIP powder grades dominate high volume tool steel markets, the advent of fine powder gas atomization has enabled the use of MIM for the production of an increasing number of industrial components where hardness and wear resistance is required. Examples include hand- and power-tool components, pump impellers and textile machinery. Tool steels typically have carbon content in the range 0.5–1.5% and heat treatment cycles are carefully controlled to achieve the optimum distribution of matrix carbides to deliver required wear performance.

Wafer-scale monolayer MoS2 grown by chemical vapor deposition using a reaction of MoO3 and H2S

Monolayer MoS2 nanosheets are potentially useful in optoelectronics, photoelectronics, and nanoelectronics due to their flexibility, mechanical strength, and direct band gap of 1.89 eV. Experimentalists have studied the synthesis of MoS2 using chemical vapor deposition (CVD) methods in an effort to fabricate wafer-scale nanofilms with a high uniformity and continuity for practical electronic applications. In this work, we applied the CVD method to a reaction of MoO3 powder and H2S gas to grow high-quality polycrystalline monolayer MoS2 sheets with unprecedented uniformity over an area of several centimeters. The monolayer MoS2 was characterized using Raman spectroscopy, photoluminescence (PL) spectroscopy, atomic force microscopy (AFM), x-ray photoemission spectroscopy (XPS), and transmission electron microscopy (TEM). The top-gate field-effect transistor prepared with a 30 nm HfO2 capping layer displayed an electrical mobility of 1 cm2 v−1 s−1 and an Ion/off of ~105. This method paves the way for the development of practical devices with MoS2 monolayers and advances fundamental research.

CFD modeling of a pilot-scale countercurrent spray drying tower for the manufacture of detergent powder

ABSTRACTA steady-state, three-dimensional, multiphase computational fluid dynamics (CFD) modeling of a pilot-plant countercurrent spray drying tower is carried out to study the drying behavior of detergent slurry droplets. The software package ANSYS Fluent is employed to solve the heat, mass, and momentum transfer between the hot gas and the polydispersed droplets/particles using the Eulerian–Lagrangian approach. The continuous-phase turbulence is modeled using the differential Reynolds stress model. The drying kinetics is modeled using a single-droplet drying model, which is incorporated into the CFD code using user-defined functions (UDFs). Heat loss from the insulated tower wall to the surrounding is modeled by considering thermal resistances due to deposits on the inside surface, wall, insulation, and outside convective film. For the particle–wall interaction, the restitution coefficient is specified as a constant value as well as a function of particle moisture content. It is found that the variation in the value of restitution coefficient with moisture causes significant changes in the velocity, temperature, and moisture profiles of the gas as well as the particles. Overall, a reasonably good agreement is obtained between the measured and predicted powder temperature, moisture content, and gas temperature at the bottom and top outlets of the tower; considering the complexity of the spray drying process, simplifying assumptions made in both the CFD and droplet drying models and the errors associated with the measurements.