The powders of the AA 7075-ZRO2 were mixed by mechanical milling, but it was found that the system presents a few disadvantages when processed by conventional sintering and hot extrusion, since intermetallic phases be...The powders of the AA 7075-ZRO2 were mixed by mechanical milling, but it was found that the system presents a few disadvantages when processed by conventional sintering and hot extrusion, since intermetallic phases between ZrO2 particles and alloying elements were formed. Equal channel angular pressing （ECAP） processing was proposed as an alternative method to consolidate the composite where there is no intermetallic formation. The analysis of the ECAP process showed that the intermediate temperature （220℃） produced a higher consolidation level than conventional sintering and hot extrusion （400 and 500℃, respectively）. This fact was supported by relative density analysis. In the case of the sintered and hot-extruded sample, the relative density exhibited a value of 0.95, while ECAP sample showed a value of 0.98. Hardness values show that microstructural refinement obtained during mechanical milling was preserved during ECAP processing even when it was carded out at 220℃.展开更多
Based on the characteristic of high energy milling and the micromechanics of composite material, a plastic constitutive equation is implemented for milled composite powders. To check the equation, the extrusion of Ti/...Based on the characteristic of high energy milling and the micromechanics of composite material, a plastic constitutive equation is implemented for milled composite powders. To check the equation, the extrusion of Ti/Al composite powders prepared by high energy milling was simulated. It was from the numerical analysis that the predicted extrusion pressure mounted up with milling time and extrusion ratio increasing, which was perfect agreement with experimental results.展开更多
The temperature and density of plasma jets were estimated with a Boltzmann plot and Stark broadening of Ar I(696.54 nm) lines by optical emission spectroscopy(OES) in the process of plasma plastic, and the morphology ...The temperature and density of plasma jets were estimated with a Boltzmann plot and Stark broadening of Ar I(696.54 nm) lines by optical emission spectroscopy(OES) in the process of plasma plastic, and the morphology and microstructure of tungsten(W) powders were investigated by scanning electron microscope(SEM) and x-ray Diffraction(XRD), respectively.The results show that the assumption of local thermodynamic equilibrium(LTE) was invalid at the end of the plasma jets, and earlier than this after the injection of tungsten powder. The temperature and electron density of the plasma jets were up to about T?=?6797 K with Qc?=?50 slpm and ne?=?1.05?×?1016 cm-3 with Qs?=?115 slpm at Z?=?60 mm, respectively, and both dropped rapidly with the injected tungsten powders of 20 μm. After the plasma plastic process,the spherical tungsten powders were prepared and there were some satellite particles on the surface of the spherical products. The tungsten powders were both composed of a single equilibrium α-W phase with a body centered cubic(bbc) crystal structure before and after plasma treatment.展开更多
An experimental investigation on the workability behaviour of sintered Fe-0.35C steel preforms under cold upsetting,have been studied in order to understand the influence of aspect ratio and lubrication condition on t...An experimental investigation on the workability behaviour of sintered Fe-0.35C steel preforms under cold upsetting,have been studied in order to understand the influence of aspect ratio and lubrication condition on the workability process.The above mentioned powder metallurgy sintered preform with constant initial theoretical density of 84% of different aspect ratios,namely,0.4 and 0.6 respectively were prepared using a suitable die-set assembly on a 1 MN capacity hydraulic press and sintered for 90 min at 1200 ℃.Each sintered preform was cold upset under nil/no and graphite frictional constraint,respectively.Under the condition of triaxial stress densification state,axial stress,hoop stress,hydrostatic stress,effective stress and formability stress index against axial strain relationship was established and presented in this work.Further more,attained density was considered to establish formability stress index and various stress ratio parameters behaviour.展开更多
The gas in plastics mould has great influence on performance, appearance and lifespan of the injection molded parts. Venting channel and its appendix system should be used for gas exhausting in general. However, the d...The gas in plastics mould has great influence on performance, appearance and lifespan of the injection molded parts. Venting channel and its appendix system should be used for gas exhausting in general. However, the dependence on the venting system complicates the mould design. Furthermore in certain condition, it is difficult to integrate the venting system into the mould. Currently a kind of mold material which has gas permeability has been developed in abroad, but the applications of this mold material were restricted by its higher cost and smaller size. In this research, a porous material which was made by powder metallurgy was applied to plastic mould to replace the venting system. Permeability of the steel with different secondary processing was tested and compared with a special apparatus. The metallographic samples of the steel with different secondary processing were prepared and investigated. Finally an actual injection set was established to investigate the applications of permeable steel. The metallographies indicate that the micro-holes inside permeable steel were interconnected. Moulds made of permeable steel exhibit good permeability in the plastic-injection experiments and gas generated in the mould cavity was smoothly exhausted. The melted plastic did not penetrate into the mould or block in the micro-holes. After several times of plastic-injection experiments, the mould still retained good permeability. The strength of this permeable steel is between 200–250 MPa and suitable for industrial applications. The venting systems simplified by permeable steel in plastic-injection have simple structures, which can be applied into any place that requires gas exhausting.展开更多
Studies were carried out to determine asbestos fiber levels in cosmetic (talc powder) and non-cosmetic (gauze pad, plastic filler and ceiling tiles) products sold in market outlets within Enugu, metropolis, Enugu Stat...Studies were carried out to determine asbestos fiber levels in cosmetic (talc powder) and non-cosmetic (gauze pad, plastic filler and ceiling tiles) products sold in market outlets within Enugu, metropolis, Enugu State, Nigeria, using standard established procedures. The samples were pretreated based on its physical make-up and the asbestos fiber levels determined using scanning electron microscopy (SEM) with energy dispersing spectroscopy techniques. The mean range of asbestos fiber was, 0.02 - 0.06;0.01 - 0.05;0.01 - 0.04 and 0.03 - 0.06 f/cc for talc powder, gauze pads, plastic filler and ceiling tile samples respectively. The mean levels of asbestos fibers in the studied samples were within the recommended permissible limits. The samples contain asbestos fiber in the following decreasing order: ceiling tiles > talc powders > gauze pads > plastic fillers. Asbestos fiber was found present in the investigated local and foreign items sold in market outlets within the metropolis. This study shows that despite the ban on the use of asbestos in the industry in the manufacture of items meant for human use, its enforcement appears weak and lethargic and this could portend health danger especially in the use of produced items with high asbestos fiber friability such as talc powder.展开更多
A simple gravity drop experiment was run to investigate plastic deformation of powder aggregrate sprayed on a hard ball under impact of another free falling hard ball and measure coefficient of restitution and plastic...A simple gravity drop experiment was run to investigate plastic deformation of powder aggregrate sprayed on a hard ball under impact of another free falling hard ball and measure coefficient of restitution and plastic strain of powder aggregate. Experimental results show that coefficient of restitution and plastic strain of powder aggregate increase as the velocity of ball increases and initial height (h 0) of powder aggregate has great effects on plastic deformation of powder aggregate. At a higher initial height (h 0), much of kinetic energy is dissipated is interparticle frictional work and coefficient of restitution is very small. Plastic strain of powder aggregate first increases as h 0 increases until a maximum value and then decreases as h 0 increases.展开更多
基金supported by Universidad Autónoma de San Luis Potosi, Centro de Investigación en Materiales Avanzados Unidad Chihuahua and Universitat Politècnica de CatalunyaFinancial support by CONACYT is appreciatedfinancial support from FAI-UASLP under the project CI5-FAI-04-45.45
文摘The powders of the AA 7075-ZRO2 were mixed by mechanical milling, but it was found that the system presents a few disadvantages when processed by conventional sintering and hot extrusion, since intermetallic phases between ZrO2 particles and alloying elements were formed. Equal channel angular pressing （ECAP） processing was proposed as an alternative method to consolidate the composite where there is no intermetallic formation. The analysis of the ECAP process showed that the intermediate temperature （220℃） produced a higher consolidation level than conventional sintering and hot extrusion （400 and 500℃, respectively）. This fact was supported by relative density analysis. In the case of the sintered and hot-extruded sample, the relative density exhibited a value of 0.95, while ECAP sample showed a value of 0.98. Hardness values show that microstructural refinement obtained during mechanical milling was preserved during ECAP processing even when it was carded out at 220℃.
文摘Based on the characteristic of high energy milling and the micromechanics of composite material, a plastic constitutive equation is implemented for milled composite powders. To check the equation, the extrusion of Ti/Al composite powders prepared by high energy milling was simulated. It was from the numerical analysis that the predicted extrusion pressure mounted up with milling time and extrusion ratio increasing, which was perfect agreement with experimental results.
基金supported by National Natural Science Foundation of China (Nos. 11805058, 11535003)Sichuan Science and Technology Program (No. 19ZDYF0012)
文摘The temperature and density of plasma jets were estimated with a Boltzmann plot and Stark broadening of Ar I(696.54 nm) lines by optical emission spectroscopy(OES) in the process of plasma plastic, and the morphology and microstructure of tungsten(W) powders were investigated by scanning electron microscope(SEM) and x-ray Diffraction(XRD), respectively.The results show that the assumption of local thermodynamic equilibrium(LTE) was invalid at the end of the plasma jets, and earlier than this after the injection of tungsten powder. The temperature and electron density of the plasma jets were up to about T?=?6797 K with Qc?=?50 slpm and ne?=?1.05?×?1016 cm-3 with Qs?=?115 slpm at Z?=?60 mm, respectively, and both dropped rapidly with the injected tungsten powders of 20 μm. After the plasma plastic process,the spherical tungsten powders were prepared and there were some satellite particles on the surface of the spherical products. The tungsten powders were both composed of a single equilibrium α-W phase with a body centered cubic(bbc) crystal structure before and after plasma treatment.
文摘An experimental investigation on the workability behaviour of sintered Fe-0.35C steel preforms under cold upsetting,have been studied in order to understand the influence of aspect ratio and lubrication condition on the workability process.The above mentioned powder metallurgy sintered preform with constant initial theoretical density of 84% of different aspect ratios,namely,0.4 and 0.6 respectively were prepared using a suitable die-set assembly on a 1 MN capacity hydraulic press and sintered for 90 min at 1200 ℃.Each sintered preform was cold upset under nil/no and graphite frictional constraint,respectively.Under the condition of triaxial stress densification state,axial stress,hoop stress,hydrostatic stress,effective stress and formability stress index against axial strain relationship was established and presented in this work.Further more,attained density was considered to establish formability stress index and various stress ratio parameters behaviour.
基金supported by Guangdong-Hong Kong Key Project of China (Grant No. 2007Z010)National Basic Research Program of China (973 Program, Grant No. 2007CB616905)
文摘The gas in plastics mould has great influence on performance, appearance and lifespan of the injection molded parts. Venting channel and its appendix system should be used for gas exhausting in general. However, the dependence on the venting system complicates the mould design. Furthermore in certain condition, it is difficult to integrate the venting system into the mould. Currently a kind of mold material which has gas permeability has been developed in abroad, but the applications of this mold material were restricted by its higher cost and smaller size. In this research, a porous material which was made by powder metallurgy was applied to plastic mould to replace the venting system. Permeability of the steel with different secondary processing was tested and compared with a special apparatus. The metallographic samples of the steel with different secondary processing were prepared and investigated. Finally an actual injection set was established to investigate the applications of permeable steel. The metallographies indicate that the micro-holes inside permeable steel were interconnected. Moulds made of permeable steel exhibit good permeability in the plastic-injection experiments and gas generated in the mould cavity was smoothly exhausted. The melted plastic did not penetrate into the mould or block in the micro-holes. After several times of plastic-injection experiments, the mould still retained good permeability. The strength of this permeable steel is between 200–250 MPa and suitable for industrial applications. The venting systems simplified by permeable steel in plastic-injection have simple structures, which can be applied into any place that requires gas exhausting.
文摘Studies were carried out to determine asbestos fiber levels in cosmetic (talc powder) and non-cosmetic (gauze pad, plastic filler and ceiling tiles) products sold in market outlets within Enugu, metropolis, Enugu State, Nigeria, using standard established procedures. The samples were pretreated based on its physical make-up and the asbestos fiber levels determined using scanning electron microscopy (SEM) with energy dispersing spectroscopy techniques. The mean range of asbestos fiber was, 0.02 - 0.06;0.01 - 0.05;0.01 - 0.04 and 0.03 - 0.06 f/cc for talc powder, gauze pads, plastic filler and ceiling tile samples respectively. The mean levels of asbestos fibers in the studied samples were within the recommended permissible limits. The samples contain asbestos fiber in the following decreasing order: ceiling tiles > talc powders > gauze pads > plastic fillers. Asbestos fiber was found present in the investigated local and foreign items sold in market outlets within the metropolis. This study shows that despite the ban on the use of asbestos in the industry in the manufacture of items meant for human use, its enforcement appears weak and lethargic and this could portend health danger especially in the use of produced items with high asbestos fiber friability such as talc powder.
文摘A simple gravity drop experiment was run to investigate plastic deformation of powder aggregrate sprayed on a hard ball under impact of another free falling hard ball and measure coefficient of restitution and plastic strain of powder aggregate. Experimental results show that coefficient of restitution and plastic strain of powder aggregate increase as the velocity of ball increases and initial height (h 0) of powder aggregate has great effects on plastic deformation of powder aggregate. At a higher initial height (h 0), much of kinetic energy is dissipated is interparticle frictional work and coefficient of restitution is very small. Plastic strain of powder aggregate first increases as h 0 increases until a maximum value and then decreases as h 0 increases.
