Effect of particle size on densification of copper powder during electric-field activated sintering for micro-scale forming

A novel Micro-forming technology, called electric-field activated sintering for micro-scale forming (Micro-FAST), was introduced for the forming of micro-components. The effect of particle size on densification is revealed for copper powder being sintered under the influence from electrical field and force-field during forming of micro-components. Three kinds of copper powders of different particle sizes ((i) average particle size of 0.5μm; (ii) average particle size of 30μm and (iii) the mixture powders with 20% weight of 30μm and 80% weight of 0.5μm) with no binder were used for the experiments. The results show that the density of the compact sintered with mixed copper powders is the largest due to more volume of liquid phase was formed in the particle's contacts. The result being in correspondence with the analytical results of computer simulation. The new understanding developed would help to better quality control during the sintering of micro-components

Fabrication of binder-free ultrafine WC-6CO composites by coupled multi-physical fields activation technology

A novel sintering method, named as coupled multi-physical fields activation technology, has been introduced for the forming of various material powder systems. Compared with the conventional ones, this technique presents more advantages: lower sintering temperature, shorter forming time, and remarkable inhibition of the grains coarsening. In the study, the cylinders of Φ4.0mm×4.0mm had been formed with ultrafine WC-6Co powders. The relative properties of sintered WC-6Co cemented carbides, such as hardness and the microstructures, had been obtained. The study has shown that a relative density, 97.80%, of the formed samples, could been achieved when the case of temperature 850℃, heating rate 50℃/s, pressure 75MPa and Electro-heating loop 6 times, were used. More importantly, the circumscription for the growth of grain size of WC, attributed to the effect of electrical field, renders coupled multi-physical fields activation technology applicable for getting WC-6Co cemented carbides with fine grain size and good properties

Sintering kinetics of the powder during fields-activated micro-forming and sintering (Micro-FAST) of copper micro-gears

Forming of micro-components from powder with fields-activated sintering technology (FAST) renders different forming and sintering mechanisms, comparing to that occurring during the forming of macro-sized components with a similar technology. Establishing a good understanding of these mechanisms would help process design and control aiming at achieving desired quality of the components to be formed. This paper presents a study and the results on the sintering kinetics of the powder during Micro-FAST for the fabrication of micro-gears (the module is 0.2 and the pitch diameter 1.6 mm) from copper powder. The results showed that the densification of copper powder is related largely to the bulk plastic-deformations of the particles and the melting of the particles at contact interfaces. Particularly, it is revealed that plastic deformations of the copper particles mainly occurred at approximately 340 °C and melting of the particle-interfaces at approximately 640 °C. Differently, in a densification process with a traditional powder sintering method, grain growth and neck growth would, normally, be two dominant mechanisms that achieve the densification of powder

A new densification mechanism of copper powder sintered under an electrical field

A new sintering mechanism is revealed for copper powder sintered under the influence of an electrical field and a force field during the formation of microcomponents. Analysis of the microstructure and grain boundary evolution of the sintered samples showed that the disappearance of the interface at contact areas between particles is a continuous process which involves new grain formation and grain refinement during this innovative microsintering process. The densification process is therefore different from what is known in a conventional powder sintering process

Forming alumina (Al2O3) by micro-FAST

The Alumina (Al2O3), also known as Aluminium oxide, has a good thermal conductivity, but it is an electrical insulator. The Alumina is being used widely in the industry. Several research the sintering of Alumina using the conventional hot pressing process or spark plasma sintering (SPS). However, these methods are and have their own limits and disadvantages, such as long process chains and low efficiency with the processes and, rarely developed for the forming of miniature and micro-scale components. In this study conducted in the report. A new process has been used adapted from the electric-current activated sintering techniques (FAST) and it is been combined with micro-forming technology and called the (Micro-FAST). The Alumina powders were loaded directly into the die, followed by electric-sintering under certain pressure. In this paper Ø4.00 mm×4.00 mm and Ø2.00 mm×2.00 mm cylinder solid samples were produced. This experiment was conducted by use of a Gleeble 3800 thermal-mechanical simulator. Several properties of the solid samples, such as relative density, ESM and EDS, were examined, and these showed good results have been obtained

Forming of titanium and titanium alloy miniature-cylinders by electrical-field activated powder sintering and forming

As demands on miniature products increase significantly, a rapid process and production system for high-throughput, highly flexible and cost-efficient volume production of miniaturised components made from a wide range of materials is needed. A novel and electrical-field-activated sintering and forming process shows the potential to produce solid parts from powder material without any binder. Using titanium (Ti) and titanium alloy (90Ti10Sn) powder material, several processing parameters have been investigated, such as pressure, heating rate, heating temperature and holding time, which helped to contribute to the optimum result. In this study, using graphite dies, graphite punches and tungsten carbide punches, solid samples were produced, having a cylinder shape of Ø4.00 mm × 4.00 mm. Several properties of the solid Ti and 90Ti10Sn samples, such as density, hardness and the microstructures, were examined, and these showed that good results have been obtained

Fabrication of micro components with MSZ material using electrical-field activated powder sintering technology

The electrical Field Activated Sintering Technology (FAST) process uses low voltage and high current, pressure-assisted sintering and synthesis technique, which has been used recently in materials processing. This method can be used to densify materials and create compounds, and it is similar to hot pressing, but the mechanism of the heating and powder densification are different. In this paper an innovative methodology has been adapted from the FAST process that can decrease the volume of the components into micro scale and called (MicroFAST). This process is a rapid powder consolidation technology and shows the possibility to produce solid parts from powder material. Using MagnesiaStabilized Zirconia (MSZ) powder material, several processing parameters have been investigated, such as pressure, heating rate, heating temperature and holding time, which helped to gain optimum results. In this paper Ø4.00mm × 4.00 mm and Ø2.00mm × 2.00 mm cylinder solid samples were shaped. The SEM and EDS have been conducted and the relative density has been examined and the results showed a very good fabricated sample with 99.83% relative density

Improvement of the fatigue life of an electron-beam welded Ti2AlNb joint subjected to an electromagnetic coupling treatment

The local stress concentration created by the seam welding process often reduces the fatigue life of the material along and around the seam. Post-welding heat treatment is usually used to improve the weld performance, but the improvement effect on fatigue life may not be obvious. In this study, a new treatment method of electromagnetic coupling was applied to regulate the Ti2AlNb electron beam weld after heat treatment, so as to improve the fatigue properties of the welded joint. The results show that after electromagnetic coupling treatment, the fatigue limit of the welded joint is increased by 10.4 %, the residual compressive stress is increased, and the fatigue crack propagation rate is decreased. The microstructure analysis shows that after electromagnetic coupling treatment, the fatigue crack source starts in the subsurface layer, the substructural crystals in the fusion zone and the heat affected zone decrease, the recrystallization content and the large angle grain boundary increase, and the dislocation density increases and tends to be homogenized. An increase of at least 2.3 % in hardness of the welded joints also indicates the increase in the dislocation density. Local high density dislocation is found in the grain, which causes dislocation entanglement and hinders crack initiation and propagation and this provides an important basis for improving fatigue properties. This study provides a new method for improving the fatigue properties of Ti2AlNb electron beam welds which can also be used to study the properties of other welded joints

An electromagnetic coupling treatment for improving the cutting performance of cemented carbide-coated tools

To improve the cutting performance and prolong the service life of a carbide-coated tool in the process of ductile iron machining, an electromagnetic coupling treatment (EMCT) was carried out. The cutting experiments show that the cutting force and cutting temperature are reduced after EMCT, and the roughness of the machined surface is reduced. It is found that after EMCT with optimal parameters the dislocation density, microscopic strain, microhardness and bonding strength of an alumina coating increase by 109.2%, 28.2%, 28.3% and 26.6%, respectively. Using the actual machining of a differential housing to verify the tool life, it is found that after EMCT, a single tool can process 18.4 more workpieces or in other words, the tool life increased by 44%. EMCT can promote element diffusion, optimize coating properties and have great potential in coating tool life extension

Improving fatigue life of a titanium alloy through coupled electromagnetic treatments

TC11 titanium alloy is widely used in the manufacture of key components such as blades of gas turbine and aero engine because of its high specific strength and good processing performance. In the case of gas turbine or aero engine, the fatigue performance of TC11 will directly determine the life of the turbine or engine, and the surface residual stress generated on the alloy during manufacturing often affects the fatigue life of the material. In this study, a new method of coupled electromagnetic treatment (CEMT) was applied to regulate the surface residual stress of the alloy after manufacturing, so as to improve the fatigue life of the TC11. The results show that after the CEMT, the residual compressive stress in the length direction and width direction increased by 63.7% and 56.0% respectively, the fatigue life of the TC11 is increased by 39.9%. The microstructure analysis shows that after CEMT, the width of fatigue striations is significantly reduced. This paper proposes that CEMT can be used as an effective method to adjust the residual stress of materials and improve the fatigue life of titanium alloys. The research is also relevant for improvement of the fatigue life of other alloy materials