High velocity compaction of 0.9Al2O3/Cu composite powder

The 0.9Al₂O₃/Cu composite powder was compacted by high velocity compaction (HVC) technique and the effects of sintering temperature on density and mechanical properties such as tensile strength and hardness were studied. The results showed that with an increase in impact velocity the green density of the compacts significantly increased. At impact velocity of 9.40 m s⁻¹, the maximum green density of the compacts reached up to 8.460 g/cm³ (RD 96.8%). The green compacts were then sintered at different temperatures and it was found that with the increase in sintering temperature the sintered density and the mechanical properties also increased. At sintering temperature of 1080 °C, the compacts obtained the maximum relative sintered density of 98%, a tensile strength of 346 MPa and hardness of 71.1 HRB. Additionally with the increase in sintering temperature, the shrinkage along both axial and radial direction increased. The electrical conductivity of the samples was measured as 71% IACS.     

Densification behaviour analysis of ZrO2 nanopowders for dental applications compacted by magnetic pulsed compaction

Sintered bulks of commercial ZrO₂ nanopowders were produced by combined application of magnetic pulsed compaction (MPC) and subsequent two-step sintering, and finally, their density, hardness, shrinkage and formability were analyzed. The formability tests were conducted by a CAD/CAM system. Nearly fully dense (∼98%) commercial ZrO₂ bulks were successfully obtained. With increasing MPC pressure, there was a decrease in the grain size of zirconia block. The ratio of PVA did not have a remarkable effect on the grain size. The optimum compaction pressure during MPC was 1 GPa and mixing conditions included using 1.0 wt. % PVA. The optimum processing condition included MPC process, followed by two-step sintering (first at 1000 and then at 1450 °C). The bulk under these conditions was found to have good formability, ∼97% density, reasonable hardness (1150 Hv) and ∼19% shrinkage.     

不同放电能量下铜粉的电磁压实特性与烧结体性能研究

目的 研究放电能量对铜粉电磁压实特性与烧结体性能的影响,提升铜材料的制备效率与质量.方法 通过电磁粉末压实技术在不同放电能量下制备铜压坯,研究压坯的相对致密度与微观形貌随放电能量的变化趋势.随后对其进行真空烧结,对烧结体的拉伸性能与断口形貌进行测试,评估放电能量对烧结体性能的影响.结果 随着放电能量的增加,铜压坯的相对...     

Comparative research on high-velocity compaction and conventional rigid die compaction

Experiments were carried out with different apparatus to compact electrolytic copper powders at distinct loading speeds. It appears that green densities of compacts prepared by HVC out-number that by conventional compaction by one percent. Compacts by quasi-static compaction are almost as dense as those by HVC under comparable peak pressure. The relationship between green compact density and peak pressure accords with Hang Pei-yun formula well. Spring-backs of HVC compacts are far smaller than those of conventional compaction and quasi-static compaction. HVC compacts are harder than compacts by conventional compaction and quasi-static compaction when they have the same density.     

Comparative research on high-velocity compaction and conventional rigid die compaction

Experiments were carried out with different apparatus to compact electrolytic copper powders at distinct loading speeds. It appears that green densities of compacts prepared by HVC out-number that by conventional compaction by one percent. Compacts by quasi-static compaction are almost as dense as those by HVC under comparable peak pressure. The relationship between green compact density and peak pressure accords with Hang Pei-yun formula well. Spring-backs of HVC compacts are far smaller than those of conventional compaction and quasi-static compaction. HVC compacts are harder than compacts by conventional compaction and quasi-static compaction when they have the same density.     

Effect of lubricants on warm compaction process of Cu-based composite

The use of lubricant is the key of warm compaction technology. Because of admixed different lubricants, the optimal parameters of warm compaction process were also different. This paper investigated the effect of two kind of lubricants (zinc stearate and polystyrene) on the parameters of warm compaction process by compared properties of Cu-based composite. It was shown that with the rise of compacting pressure, the density and hardness of the Cu-based composite increased, but the resistivity and gaining weight reduced. With increasing compacting temperature, the density and hardness first increased and then decreased, but the trend of resistivity and gaining weight just reversed. For the samples admixed zinc stearate (ZS), the optimal admixed concentration was 0.4 wt%, and the sample prepared at 120 °C and 650 MPa had the highest density and hardness, the lowest resistivity and gaining weight. For the samples admixed polystyrene (PS), these parameters were 0.7 wt%, 140 °C and 650 MPa, respectively. The properties of samples admixed PS were superior to that of admixed ZS.     

Effect of impact force on Ti–10Mo alloy powder compaction by high velocity compaction technique

Ti–10Mo alloy powder were compressed by high velocity compaction (HVC) in a cylinderical form of height/diameter (h/d) in die 0.56 (sample A) and 0.8 (sample B). Compactions were conducted to determine the effect of impact force per unit area of powder filled in die for densification and mechanical properties of Ti–10Mo samples. The micro structural characterization of samples were performed by scanning electron microscope (SEM). The mechanical properties of the compressed samples such as Vickers hardness, bending strength, and tensile strength were measured. Experimental results showed that the density and mechanical properties of sample A and sample B increased gradually with an increase in impact force and decreased with an increase in height/diameter ratio. The relative green density for sample A reached up to 90.86% at impact force per unit area 1615 N mm⁻². For sample B, it reached 79.71% at impact force per unit area 1131 N mm⁻². The sintered sample A exhibited a maximum relative density of 99.14%, Vickers hardness of 387 HV, bending strength of 2090.72 MPa, and tensile strength of 749.82 MPa. Sample B revealed a maximum relative sintered density of 97.73%, Vickers hardness of 376 HV, bending strength 1259.94 MPa and tensile strength 450.25 MPa. The spring back of the samples decreased with an increase in impact force.     

Consolidation of mixed diamond and cobalt granule powders by magnetic pulsed compaction

Magnetic pulsed compaction (MPC) was introduced to consolidate mixed diamond and cobalt (Co) granule powders for the production of drilling segments. The diamond-Co samples prepared by MPC at the compacting pressure of 4 GPa showed a high sintered density of 99.6% as well as a high green density of 86.4%. A fine and homogeneous microstructure and a high hardness were also observed in the sintered bulk. Finally, a perforating test revealed that a higher drilling speed of 11.71 cm/min and a longer tool life of 7.96 m were obtained for the drilling segments prepared by the MPC process, whereas the values for those fabricated by a conventional process were 10.15 cm/min and 6.55 m, respectively. This property improvement of the MPCed segments was attributed basically to the enhanced green density and the homogeneous distribution of the diamonds.     

Hot shock compaction of nanocrystalline alumina

An experimental investigation of hot shock compaction of a nanocrystalline alumina powder was performed. The effects of variations in shock pressure and compaction temperature on the properties of the compacted materials were studied. It was found that the bulk density and hardness of the compacted material increased with shock pressure. Increasing compaction temperature resulted in increases in compact hardness and bonding, and reductions in cracking within the compacted specimens. The results suggest that dense, well bonded, crack free nanocrystalline ceramics may be fabricated more effectively using hot shock compaction, than by room temperature shock compaction followed by sintering or room temperature static compaction followed by sintering.     

Compaction of different boron carbide powders using uniaxial die compaction and combustion driven compaction

Compaction of pure B₄C and Ni₂B nanolayer coated B₄C was studied using uniaxial die compaction and combustion driven compaction techniques. Effects of different compaction techniques and the Ni₂B nanolayer around B₄C particle surfaces on green B₄C sample characteristics are the focus of this study. The combustion driven compaction process yields much higher green density and strength than the uniaxial die compaction process. For the samples obtained from the same compaction technique, the Ni₂B nanolayer on individual B₄C particle surfaces improves the green density and strength of the B₄C powder compacts. For the combustion driven compaction process, optical images show micro-cracks on the surface of pure B₄C compact while crack-free surface is observed for Ni₂B nanolayer coated B₄C sample. Scanning electron microscopy analysis shows the same trend as the green density and strength measurements. Combustion driven compaction diagram for hard and brittle materials such as B₄C is discussed.     

Effect of liquid phase on densification in electric-discharge compaction

The effect of liquid phase on densification in electric-discharge compaction (EDC) was explored in the present work. The temperature at contact area of particles in EDC was estimated from random packing model incorporated with electric current distributions. Consolidation of cemented carbide and tungsten heavy alloys was conducted under varying current densities. WC-11Co/Fe/WC-11Co sandwich powder compacts were designed to investigate the effect of liquid phase flow. It is found that the densification occurred only when liquid phase formed, and relative density increased with the increasing of liquid phase volume. In the case of WC-11Co powders, the faceted grain evolution occurred but the significant grain growth was hardly observed, which meant the densification was mainly induced by particle rearrangement. The depth of liquid penetration of Fe in WC-11Co/Fe/WC-11Co sandwich compact also agreed with that caused by particle rearrangement processing. The possible effects of electric current on densification were also discussed.     

The effect of ultrasonic vibration on the compaction characteristics of ibuprofen

An ultrasonic (US) compaction rig has been developed, capable of providing compaction pressure together with high-power ultrasonic vibrations of 20 kHz to a powder or granular material in a die. The rig has been used to investigate the effect of ultrasound on the compaction properties of ibuprofen, a drug with poor compaction properties which produces tablets that are weak and frequently exhibit capping. It was found that coherent ibuprofen tablets could be prepared by ultrasound-assisted compaction at pressures as low as 20-30 MPa. Application of ultrasound before and after compaction was found not to be as effective as ultrasound applied during compaction. The breaking forces of the tablets produced with ultrasound applied during compaction were found to be consistently significantly higher than when compaction was performed conventionally, or with ultrasound applied before or after compaction. Application of ultrasound during compaction made it possible to increase tablet mechanical strength, typically by a factor of 2-5. It was concluded that pressure should be applied together with ultrasound in order to achieve a better acoustical contact, which is required to transmit vibrations from the horn to the material, and also to bond the surfaces of the particles.

Ultrasound application during ibuprofen compaction also resulted in an increase in the apparent density, in relation to the apparent density of conventionally prepared tablets, of up to 14.4%. Ultrasound appears to improve particle rearrangement and provides energy for partial melting of particle asperities and subsequent fusion of particle surfaces, so as to increase interparticulate bonding. Solid bridge formation was thought to result in a reduction of void space, which in turn reduced the rate of water penetration into the compacts and consequently increased disintegration and dissolution times.

It was found that the results of ultrasound-assisted compaction are influenced by formulation and US time. When ibuprofen was mixed with a second material, such as dibasic calcium phosphate dihydrate (DCP) or microcrystalline cellulose (MCC), stronger tablets were prepared by ultrasound-assisted compaction compared to the compacts containing no filler. Positive interactions were considered to have occurred due to ultrasound-induced bonding between the two materials. With an increase in DCP and MCC concentration in ibuprofen formulations, disintegration and drug dissolution rates of the tablets produced with ultrasound significantly increased.

Using temperature-sensitive labels it was found that thermal changes occurred in powdered solids undergoing ultrasound-assisted compaction. Increases in the temperature of tablets were related to US amplitude and US time. With an increase in US amplitude from 5 to 13 µm, the temperature of the DCP tablet surface increased from 40 to 99°C. With an increase in US time from 1 to 5 sec, the temperature of the surface of ibuprofen tablets increased from 43 to 60°C. Increased tablet temperature was thought to be due to ultrasonic energy dissipation turned into heat.

X-ray powder diffraction (XRD) studies of ibuprofen tablets prepared by ultrasound-assisted compaction at 32 MPa revealed that no changes in chemical or/and crystalline structure of the material occurred when ultrasound was applied for up to 5 sec (US amplitude 7 µm). An XRD study of DCP tablets produced by ultrasound-assisted compaction at 32 MPa with ultrasound of different amplitudes (5, 7, 13 µm) applied for 2 sec indicated that no material deterioration occurred in all the tested samples.     

Effect of particle size distribution on green properties during high velocity compaction

Iron powders with two different particle size distributions were compacted by high velocity compaction. The influences of particle size distribution and impact velocity on green properties, including green density, springback, tensile strength and bending strength etc., were studied with scanning electron microscopy (SEM) and a computer controlled universal testing machine. The results show that the particle size distribution and the impact velocity strongly affect its properties. Wider size distribution results in green compact with higher density and better strength. Furthermore, springback of compacts is lower produced by the powder with wider size distribution, especially for radial springback. As impact velocity increases, its green density and green strength gradually increases, but the increasing rate of density decreases gradually. No special relation is found between springback and impact velocity. In addition, the axial springback and the bending strength are higher than the radial springback and the tensile strength, respectively.     

铁粉的高速压制成形

采用高速压制技术制备铁基制品,探讨了冲击能量及冲击速度与冲击行程之间的关系,并研究了冲击能量、压制方式对生坯密度、最大冲击力、脱模力和径向弹性后效的影响.结果表明:在高速压制过程中,冲击能量与冲击行程呈线性关系,而冲击速度与冲击行程呈抛物线关系.生坯密度随着冲击能量的增加而逐渐增大.单次压制时,当冲击能量增加到6510 J时,生坯密度达到7.336 g/cm~3,其相对密度约为97%.在总冲击能量相同的情况下,两次压制制备出的试样生坯密度最大,三次压制的最小.在高速压制过程中,试样的脱模力及其径向弹性后效均远低于传统压制.     

Effect of particle size distribution on green properties during high velocity compaction

Iron powders with two different particle size distributions were compacted by high velocity compaction. The influences of particle size distribution and impact velocity on green properties, including green density, springback, tensile strength and bending strength etc., were studied with scanning electron microscopy (SEM) and a computer controlled universal testing machine. The results show that the particle size distribution and the impact velocity strongly affect its properties. Wider size distribution results in green compact with higher density and better strength. Furthermore, springback of compacts is lower produced by the powder with wider size distribution, especially for radial springback. As impact velocity increases, its green density and green strength gradually increases, but the increasing rate of density decreases gradually. No special relation is found between springback and impact velocity. In addition, the axial springback and the bending strength are higher than the radial springback and the tensile strength, respectively.     

Shock compaction of silicon carbide powder

A series of shock compaction experiments on SiC powder were carried out over a wide range of shock pressures and shock temperatures up to 30 GPa and 3400 K. Large changes in some physical properties and a variety of unique microstructures were observed in the shock-treated samples with changes in impact conditions. For an iron plate impactor, the optimum impact condition, which depends on the initial density, is 2.5 km sec^–1 for 70% initial density and 2.0 km sec^–1 for 50%. The best-sintered compact of SiC with 97% density and micro-Vicker's hardness of 2700 kg mm^–2 was obtained under optimum conditions. Good compacts with high relative density and high strength exhibit the disruptive effects of the shock wave, which are indicated by microstrain increase and crystallite size reduction. The skin model is presented here in order to estimate the heterogeneous shock state which is realized under and after shock loading of the initial powder aggregates.     

Fabrication and properties of hollow powder porous structures

Low-cost steel porous structure materials have been prepared from hollow sphere mill-scale powders by using a simple method. Hollow spheres of mill-scale material were fabricated by coating polystyrene spheres, using pelletizer disc. The coated powders were mixed with 1 wt.% inorganic binder diluted in 4 wt.% water, and then were uniaxially pressed at 0, 100, 200 and 400 MPa in a die to produce rectangular shape compacts (30×15×15 mm), calcined at 550 °C for 30 min (to burn off the organic materials). After calcination, the compacts were then sintered in hydrogen atmosphere for 40 min at 1150 °C.The resulted steel porous materials have different relative densities varied from 32.3% to 50.89%, depending upon the previous compaction pressing before sintering. It is noted that the relative density increased with the increase of compaction pressing, whereas the porosity content decreased. Increase of properties, such as hardness, transverse rupture strength, and compression yield stress, occurred due the increase of compaction pressing of the compacts before sintering.     

Investigation on the effect of lubrication and forming parameters to the green compact generated from iron powder through warm forming route

In order to generate green compacts of iron ASC 100.29 powder at above ambient temperature and below its recrystallization temperature, a warm compaction rig is designed and fabricated which can be operated at various temperature and load. The aim of this paper is to present the outcomes of an investigation on the effect of lubrication and forming parameters, i.e., load and temperature to the green compacts generated through warm compaction route. The feedstock was prepared by mechanically mixing the main powder constituent, i.e., iron ASC 100.29 powder with different weight percent of zinc stearate at different mixing time. Compaction load was varied from 105 kN to 125 kN using simultaneous compaction mechanism. The microstructures of the green compacts were analyzed by Scanning Electron Microscopy (SEM), and the mechanical properties are measured through density measurement, hardness test and electrical conductivity test. The study found that increase in compaction load as well as forming temperature give improved microstructure and mechanical properties. It is also found that effects of lubrication to the mechanical properties of green compacts are strongly dependant on the lubricant content as well as mixing time of iron powder with the lubricant.     

Comparative Evaluation of A New Direct Compression Excipient, SoludexTM 15

Soludex^TM15, a new corn-based maltodextrin, has been evaluated and compared to nine frequently used commercial excipients for direct compression. The properties of the excipients reported are median size, particle size distribution, bulk density, flow rate, repose angle, moisture content, and hardness and compressibility at several compaction pressures. The influence of concentration of lubricant and mixing time with a lubricant on hardness of Soludex 15 compacts were determined. The effect of 1% magnesium stearate on the hardness of compacts was determined for the ten excipients. Model formulations for direct compression tablets using Soludex 15 are presented, and for a batch of these tablets the weight variation, friability, hardness, disintegration and dissolution are reported. Soludex 15 exhibited excellent flow and compressibility, and model tablets using Soludex 15 as the direct compression diluent met USP specifications and provided a rapid dissolution of the active ingredient.     

Ultrasonic Characterization of Iron Powder Metallurgy Compacts during and after Compaction

Ultrasonic measurements in powder metallurgy (PM) compacts at various stages of production are presented both as a practical means of improving PM production and as a method of providing a fuller understanding of PM materials. Ultrasonic monitoring during powder compaction, a novel process instrumentation technique to follow powder densification, is reviewed. Measurements taken during the compaction of simple PM disk demonstrate that the ultrasonic velocity can be used as a measure of the in situ density. This connection arises due to the acoustic equivalence between powder during compaction and PM compacts after sintering. Ultrasonic monitoring during compaction of a two-level PM part is demonstrated to be fully capable of independently following the density in each level. The results also provide evidence of different regimes of powder flow behaviour during compaction. Ultrasonic velocity mapping of the two-level compact after sintering provides confirmation of the monitoring results. Subsequently, measurements of the ultrasonic velocity in green PM compacts are shown to be consistent with a dependence on the quality of inter-particle bonding. Finally, laser ultrasonic measurements in PM compacts are used to determine the ultrasonic attenuation. Attenuation values in a sintered compact are shown to follow a simple Rayleigh scattering dependence on frequency which yields a powder particle size consistent with the known value.