Dynamic Powder Compaction Research Articles

Aluminum coatings via kinetic spray with relatively large powder particles

Coatings have been produced by entraining relatively large diameter metal powders in a supersonic airflow. For the first time, most of the particles in the powders have diameters >50 μm. Substantial plastic deformation is involved in the conversion of the particle's kinetic energy into heat and strain energy in this kinetic spray process. As suggested by simple estimates and confirmed by coating grain structures, the particles are not melted or thermally softened in this coating process. These coatings have a relatively low oxide content, low thermal stress, high adhesion, low porosity and hardness somewhat higher than those of corresponding bulk materials. Threshold or critical velocities for coating formation are discussed. Critical velocities for the relatively large particles were observed to be substantially less than have been reported earlier for smaller diameter (<50 μm) particles. Coating particle rotation and deformation due to particle impact resulted in a corresponding decrease in porosity. Bond formation, particle deformation and grain deformation were found to be highly anisotropic, depending on the direction of the incident particle velocity. At higher incident velocities, increasing metallic bond formation between particles was observed. This is consistent with a metallic form for stress/strain curves obtained via tensile tests on Al coatings removed from the substrate. The coating elastic modulus was found to be less than half that of bulk Al. Measured ultimate tensile strengths and yield points of Al coatings were comparable to those of bulk Al. This may be due to work hardening resulting from the plastic deformation necessary for coating formation. These tensile test results are consistent with coating cohesive strengths as measured by stud pull tests. Higher powder feed rates produced coatings with higher failure loads in three point bending, higher coating cohesion and lower coating strength anisotropy, presumably due to a peening effect. Four velocity-dependent stages of coating formation are proposed based on observations reported here. Coating properties arise from a competition between these stages. Parallels with models of dynamic (explosive) powder compaction are made. This is the first comprehensive model for kinetic spray coating formation.

Analysis of dynamic powder compaction

Analysis of dynamic powder compaction

Dynamic powder compaction for parts with high-aspect ratio

A computer program has been developed to analyse one-dimensional elasto-plastic wave propagation in a powder-filled container. A numerical integration along characteristic curves is introduced in this program. Characteristic curves are derived from an equation of motion, a constitutive equation and a compatibility equation. In the constitutive equation, the effect of strain rate is taken into consideration. Using this computer program, loading conditions to obtain uniform strain distribution are examined, varying parameters such as the duration and peak of impulses. The following results were obtained: (1) the increase in strain near the fixed end of the container caused by the reflection of the plastic wave contributes to the uniform strain distribution; (2) this wave reflection has the same effect as the usage of a floating die; and (3) for the part with a specific aspect ratio, there is an optimum condition of the duration and peak of the impulse.

Ｍａｌｖｅｒｎ型構成方程式を用いた金属粉末の動的圧粉解析

In powder Metallurgy process, some dynamic powder compaction methods have been proposed because they have advantages of giving uniform density distribution even for high-aspect-ratio parts and breaking surface oxides of powders, comparing with static powder compaction methods.Constitutive equations considering strain-rate effect are usually used to analyze the dynamic deformation of solid materials. One-dimensional dynamic analyses using static stress-strain relations were carried out so far. However, in case of powder materials, constitutive equation considering the strain-rate effect has not been applied.In this paper a Malvern-Type constitutive equation, Ee=σ+K(σ-f(e)) for powder materials is employed to analyze dynamic behavior of powder materials. A constant, K, in the equation is obtained by comparing the experimental and analytical results in terms of plastic strain distribution at longitudinal in a container. In the case of rapidly solidified Al-Li powder, K=2×105 is obtained.This method can widely be applicable to get dynamic constitutive equations for powders.

Simulation of dynamic compaction of metal powders

This article presents numerical studies on the deformation of particles during dynamic compaction of metal powders. The analysis of the process is based on a micromechanics approach using multiple particle configurations. The material considered is elastoviscoplastic with interparticle friction. Two-dimensional studies on particles in close packed arrangement were carried out using plane strain conditions for deformation and thermal response. The finite element method using an explicit dynamic analysis procedure was used for the simulations. The influence of speed of compaction, strain hardening, strain rate dependency, interparticle friction and size of the powder particles on the final shape and temperature variations within the particles were analyzed. The studies offer useful information on the shape and temperature variations within the particles. The results provide a better understanding of the dynamic compaction process at the micromechanics level.

動的圧粉体に及ぼすパンチ形状の影響

In the present study, the thin film forming of pure aluminum powders is carried out by a dynamic compaction method. The influence of processing parameters on the density, mechanical properties and microstructures of compacted powders is investigated. The control of stress wave is also attempted in order to obtain a high compacting stress due to the superimpose of stress waves. The dynamic powder compaction is carried out by an electromagnetic induction method. This method allows easy control of stress pulse. Two kinds of punches with a straight shape and a sudden increase in cross section are used for the dynamic powder compaction. Pure aluminum powders of 37, μm in average are used as a raw material for the compaction. The compactions are carried out at room temperature in air. A density measurement shows that the compacted Al powders have a relative density of 0.90-0.97. As the stress has increased with a superimpose of the incidence stress wave and reflection stress wave in using the punch with the sudden increase in cross section, the bending strength of the compacted powders is stronger than the one in using the punch with a straight shape.

An improved high-temperature shock compression and recovery system using underwater shock wave for dynamic compaction of powders

Abstract A high-temperature shock compression system using converging underwater shock waves has been developed and the performance is under attempted improvement in the present investigation. A maximum temperature of 1100°C was obtained, and the use of PBX explosive with detonation velocity of 8.5 km s−1 gave us the higher shock pressure. Also, scaling up the size of the experimental apparatus especially in the size of explosive made possible an increase in the duration of shock pressure. Small fragments of consolidated diamond powders were recovered due to difficulty of recovery of the new system, but the sample showed very high Vickers hardness above 60 GPa.

Ion-Beam Driven Shock Loading Device for Compaction.

Ion-beam driven shock loading device is proposed to make efficient dynamic compaction of nanocrystal and non-equilibrium powders. Different form the conventional gas-guns and powder fire-guns, the repetitive application of shock pressure pulse to targeting materials and the fine control of pressure pulse are intrinsic features to the present approach. Since the generated plasmoid is electro-magnetically accelerated to launch the flyer, no limitation to flyer velocity is present. The laser doppler velocimetry is used to make real time measurement of copper flyer velocity. The efficiency is estimated to be about 6 % for conversion from the accumulated energy in the condenser bank to the kinetic energy of a flyer.

Effects of temperature rise on dynamic powder compaction

The effects of temperature rise caused by plastic deformation and friction on one-dimensional dynamic powder compaction are made clear. The numerical integration of the equation of motion shows that temperature rise is influenced by the peak values of the dynamic load and the friction. In the vicinity of both ends of the powder, the temperature rises with increase in the dynamic load. For greater coefficients of friction, the temperature rises remarkably near to the impact end, the maximum temperature rise of 40°C being observed at the impact end for the dynamic load condition of P 0 = 500 MPa, T = 100 μs, μ = 0.25. The temperature rise reduces the stress and the wave propagation speed, whilst the strain increases slightly.

Dynamic compaction of powders by an oblique detonation wave in the cylindrical configuration

A new method has been applied to dynamically compact ceramic powders in the cylindrical configuration. In this method, a converging oblique detonation is used instead of the sliding detonation used in the standard method. The oblique detonation is generated by a configuration using two explosive layers. X-ray flash photographs have been made that show the detonation and shock fronts in both the standard and new configuration. In the present article, the shock wave and particle velocities in the B4C powder have been calculated using the shock and detonation angles obtained from the photographs in combination with the measured detonation velocity. In the two-layer configuration, the pressure applied to the powder was increased by a factor of 3.5 compared to the one-layer configuration, in agreement with calculations. The working principle of the two-layer configuration is discussed and compared with a computer simulation of the process.

The calculation of the shock velocity — particle velocity relationship for a copper powder by direct numerical simulation

The dynamic compaction of ceramics, oxide superconductors, and superhard materials is an active area of research world-wide. The current knowledge about shock processes in materials is based primarily on phenomenological modeling. In order to optimize the dynamic powder compaction process, a detailed understanding of the micromechanical behavior of the powder during the compaction process is necessary. As a first step, the shock compaction of a moderate number (~100) of discrete powder particles is simulated with an explicit Eulerian finite element program. To verify the accuracy of the calculations, the relationship between the particle velocity and the shock velocity for a copper powder has been calculated and compared to experimental results. Copper was chosen for these calculations because of the extensive experimental results that are available in the literature.

Analysis of dynamic deformation mechanisms in powder metals

In this paper, numerical analysis of stress wave propagation in powder by a characteristic method is presented. The results of the dynamic analysis show the distribution of time-dependent parameters; stress, strain, density, particle velocity, and wave propagation speed. The results prove that the powder has different dynamic behavior as compared with ordinary solid materials, because of its peculiar mechanical properties which depend on the density.Owing to the density change, the wave propagation speed of elastic and plastic waves increases with stress increment. Moreover, the following processes are made clear. The loading wave front gets sleeper with its propagation. After the peak of the stress, an unloading wave takes place. Another secondary elastic wave is caused by the unloading wave.These results obtained by the analysis may be effective in the breaking an oxide surface layer covering aluminum powder, and for controlling density distribution under the dynamic powder compaction.

Synthesis and dynamic compaction of ceramic nano powders by techniques based on electric pulsed power

Studies on the production of nanometer-sized powders by the exploding wire method were conducted. The aim of the work was to attain a particle distribution with a high yield of particles below 20 nm in size. Powders of alumina and titania were generated during the experiments by maintaining a definite partial pressure of oxygen inside the explosion chamber. The particles are spherical in shape with specific surfaces up to 100 m 2/g. The output capacity is on the order of 1 kg/h with an energy consumption of 2 kWh/kg. Alumina powders crystallize in the gamma and delta structures, titania powders consist of anatase and rutile. The second part of the studies deals with the compaction of nano-sized powders by application of pulsed electro-magnetic power. For the compaction of nano-sized Al 2O 3 powder pressure pulses in the range from 1 GPa to 5 GPa, lasting 3 – 300 μs, were applied. The simply shaped bulk samples maintained a nano-crystalline structure and reached 62 to 83 % of the theoretical density.

Dynamic magnetic consolidation and compaction of tungsten alloy powders: B. Chelluri et al (IAP Research Inc, USA)

Dynamic magnetic consolidation and compaction of tungsten alloy powders: B. Chelluri et al (IAP Research Inc, USA)

Different types of dislocations in YBa2Cu3O7- delta.

In the present study, dense pellets of polycrystalline YBa2Cu3O7-delta were made by dynamic powder compaction. The shock wave, which passes through the initially loose powder, generates multiple defects. Its hydrostatic component suppresses the brittle nature of YBa2Cu3O7-delta, and so plastic deformation such as dislocation generation and glide is expected. This paper reports on the characterization of structure defects observed in shock loaded samples, compacted at E/M ratios ranging from 0.8 to 2.3. The microstructure of shock compacted samples is compared to that of the initial, noncompacted powders. Apart from the well-established [100](001) glide system, two additional glide systems have been identified: [110](110BAR) and [010](100). They are characterized both by diffraction contrast and high-resolution transmission-electron-microscopy techniques. The interaction between the different types of dislocations and other structure defects, as well as their role in cleavage and stacking fault generation is investigated. Finally, the possible role in flux pinning of the dislocation types is briefly discussed.

Die stress and internal friction during quasi-static and dynamic powder compaction

Die stress and internal friction during quasi-static and dynamic powder compaction

Die stress and internal friction during quasi-static and dynamic powder compaction

Three commercial iron powders have been studied in terms of their particle morphology and frictional characteristics. The frictional characteristics were measured in shear cell experiments at normal applied loads of up to 4.7 MPa and deduced from measurements of axial stress and radial stress in an instrumented die used in quasi-static and dynamic compaction experiments at axial stresses of up to 300 MPa. Particle shape factor and specific surface area did not greatly affect the coefficient of internal friction. For the range of powder parameters considered, it was most affected by particle size with the smaller particle samples having the higher friction. There was good qualitative agreement between the coefficient of internal friction deduced from shear cell and die pressing experiments. Despite evidence of the development of cohesion in the powders in the die pressing experiments, the linearity of the axial stress-radial stress relations suggested that the powder response could be characterised in terms of a constant value of the coefficient of internal friction. In dynamic compaction, appreciably lower radial stresses are developed. This is consistent with a higher value of internal friction under these loading conditions.

Shock wave compaction of powders and porous bodies — dynamic compaction of powders in rigid dies

Shock wave compaction of powders and porous bodies — dynamic compaction of powders in rigid dies

Dynamic compaction of amorphous Nd15Fe77B8 alloy powders

Dynamic compaction of amorphous Nd15Fe77B8 alloy powders

Numerical modeling of dynamic powder compaction using the Kawakita equation of state

Dynamic powder compaction is analyzed using the assumption that the powder behaves, while it is being compacted, like a hydrodynamic fluid in which deviatoric stress and heat conduction effects can be ignored throughout the process. This enables techniques of computational fluid dynamics such the equilibrium flux method to be used as a modeling tool. The equation of state of the powder under compression is assumed to be a modified version of the Kawakita loading curve. Computer simulations using this model are performed for conditions matching as closely as possible with those from experiments by Page and Killen [Powder Metall. 30, 233 (1987)]. The numerical and experimental results are compared and a surprising degree of qualitative agreement is observed.