A method to fabricate the metallic closed cellular material has been developed. Powder particles of polymer coated with a nickel-phosphorus alloy layer using electro-less plating were pressed into pellets and sintered at high temperatures by a furnace and a spark plasma sintering (SPS) system. A metallic closed cellular material containing different materials from that of cell walls was then fabricated. The mechanical properties of this material were measured. The results of the compressive tests show that this material has the different stress-strain curves among the specimens that have different thickness of the cell walls and the sintering temperatures of the specimens affect the compressive strength of each specimen. Also, it seems that the results of the compressive tests show that this material has high-energy absorption and Young's modulus of this material depends on the thickness of the cell walls and the sintering temperature. These obtained results emphasize that this material can be utilized as energy absorbing material and passive damping material.
Particles dispersively coated with other material is a kind of composite particles, i.e., core particles are dotted with other material. Two methods have been developed for such the composite particles. One is a forced electrification method and the other a rotating drum method. The former utilizes the electrostatic force, i.e., positively electrified core particles and negatively electrified child particles are mixed. The latter is a mechanical method as follows. Core particles and child particles are charged into a cylindrical vessel, and mixed by rotating the vessel for several hours. We prepared composite particles of PTCR (Positive Temperature Coefficient of Resistivity) barium titanate and the junction metal such as indium and solder. When the composite particles are filled, the junction metal always exists between the neighboring core particles. The PTCR property of the filling is almost the same with that of the sintered barium titanate. We fabricated a PTCR thin sheet by packing the composite particles between two sheet electrodes. If the composite particles are electrically connected but fixed not firmly, the sheet shows PTCR property and can bend by rearrangement of the particles. Thin ceramics sheet is practically impossible because of the brittleness. However, flexibility can be given to the sheet of the PTCR-junction metal composite particles. The composite particles are fixed by enveloping in an evacuated bag or by embedding in a heat resistant resin. Advantages and disadvantages of the preparation methods and fabrication methods are discussed. Preliminary experiments for a new approach to the PTCR sheet are introduced.
New method to fabricate the metallic closed cellular material containing organic materials for the damping systems has been developed. Powder particles of polystyrene coated with a nickel-phosphorus alloy layer using electro-less plating were pressed into pellets and sintered at high temperatures by a furnace and a spark plasma sintering (SPS) system. A metallic closed cellular material containing polystyrene was then fabricated. The physical, mechanical and damping properties of this material were measured. The density of this material is smaller than that of other structural metals. The results of the compressive tests show that this material has the different stress-strain curves among the specimens that have different thickness of the cell walls and the sintering temperatures of the specimens affect the compressive strength of each specimen. Also, it seems that the results of the compressive tests show that this material has high-energy absorption and Young's modulus of this material depends on the thickness of the cell walls. The loss factor of this material was measured and the results show that this material has a large loss factor than that of structural metals. These obtained results emphasize that this metallic closed cellular material can be utilized as energy absorbing material and passive damping material.
Recently our group has succeeded, by producing very small particles of NbC carbides in austenite, in improvement of shape memory effect (SME) of the low-cost conventional Fe-Mn-Si based SMAs to such an extent that the so-called "training" treatment is no longer necessary. It was also found that the shape memory properties of the Fe-Mn-Si based SMAs were further improved by pre-rolling at 870K. The present paper describes similar improvement of shape memory properties of an Fe-15Mn-5Si-9Cr-5Ni-0.5NbC (mass %) by more convenient way of pre-extension at room temperature. This alloy is high corrosion-resistant (equivalent to SUS430) as well as low cost material, which is also one of the important requisites for industry application in various fields. A nearly perfect shape recover (90%) of an initial 4% strain was achieved when the alloy was pre-extended 12% at room temperature and then aged at 1070K for 10min. The origin of this improvement of SME has been studied by atomic force microscopy (AFM) and trasmission electron microscopy (TEM). It is concluded that uniform distribution of fine martensite plates with the same variant on the primary system is the key factor to obtain a perfect shape memory recovery.
By addition of small amount of Nb and C to the conventional Fe-Mn-Si based shape memory alloys, shape memory properties are greatly improved in such an extent that the costly 'training' heat treatment is no more necessary. The key to this remarkable improvement of shape memory effect is to produce small NbC precipitates of about several nm in size in austenite. In order to generate such very small NbC particles, the sample is firstly rolled at 870 K and then aged at 1070 K. An example of Fe-28Mn-6Si-5Cr-0.53Nb-0.06C (mass %) alloy is shown; 95% shape recovery for initial strain of 4% is obtained and the shape recovery stress of about 300 MPa is attained for the sample pre-rolled 14%, which is well above the criterion for industry application of pipe jointing. A pipe jointing with this material is demonstrated.
A metallic closed cellular material containing organic materials for the smart materials has been developed. Powder particles of polystyrene coated with a nickel-phosphorus alloy layer using electroless plating were pressed into green pellets and sintered at high temperatures. A metallic closed cellular material containing organic materials was then fabricated. On the fabricated metallic closed cellular materials, compressive properties, Young's modulus, ultrasonic attentuation coefficient internal friction were measured. The compressive tests shows that this material has the different stress-strain curves among the specimens that have different thickness of the cell walls. Each stress-strain curve has a long plateau region, the sintering temperatures of the specimens affect the compressive strength of each specimen, and energy absorbing capacity is very high. Young's modulus of this material depends on the thickness of the cell walls and the sintering temperature. The attenuation coefficient of this material observed by ultrasonic measurement is very large. Internal friction of this material is very large and depends on the sintering temperaturer. These results indicate that this metallic closed cellular material can be utilized as energy absorbing material and passive damping material.
Material damage is too fine to be detected by non-destructive tests and difficult to be repaired during use. Therefore self-healing of damage is most desirable to improve the reliability of materials and structures. In heat resisting steels, creep cavities nucleate at grain boundaries by long time use at high temperatures. These creep cavities grow along grain boundaries, from grain boundary cracks by linking up each other and cause the premature and low ductility fracture. Therefore long time creep rupture life and ductility chiefly depend upon the behavior of nucleation and growth of creep cavities. If the growth of creep cavities could be suppressed, the creep rupture properties of creep rupture life and ductility should be improved due to prevention of the premature fracture. Ordinary austenitic stainless steels contain sulfur as impurity and the sulfure segregates preferentially to creep cavity surface because of its high surface actiivty. It is possible to remove sulfur almost completely by doping cerium and adding titanium to the austenitic stainless steels. By adding boron and nitrogen, boron nitride precipitates on creep cavity surface. It was thought that the boron nitride on creep cavity surface suppresses creep cavity grwoth and improve creep rupture life and ductility by its healing effect on cavities.
KEYWORDS: Diffusion, Cavitation, Cerium, Chemical compounds, Scanning electron microscopy, Process control, Control systems, Electron microscopes, Corrosion, Reliability
In heat resisting steels, micro holes, called creep cavities, are formed at grain boundaries by long term use at high temperatures. These creep cavities grow along grain boundaries, form grain boundary cracks by linking up each other anc cause low ductility and premature fracture as shown in Fig. 1. Therefore long term creep rupture strength and ductilities chiefly depend upon the behavior of nucleation and growth of creep cavities. If the growth of creep cavities could be suppressed, creep rupture strength and ductilities should be improved remarkably. Present work is intended to propose a self-healing process for the cavitation, and improve the creep rupture properties by the self-healing. It is thought that chemical compound of BN precipitates at inside surface of creep cavity by addition of B and N to heat resisting steels. As the BN is very stable at high temperatures, the precipitation of BN at creep cavity surface is expected to suppress the creep cavity growth and bring about the healing effect on the cavitation.
Electroceramic particles with electrodes of solder are prepared y a low cost and high productivity process. The electroceramic particles can be used as single particle devices, and moreover as multi-functional devices by their assembling. PTCR material is one of the electroceramics, having a positive temperature coefficient of resistivity. We prepare the PTCR particles with electrodes of solder as follows. Semiconducting barium titanate (BaTiO3) particles, a typical PTCR material, and solder particles are charged into a cylindrical vessel, and the vessel is rotated for several hours. The product is semiconducting BaTiO3 coated by solder particles. The solder particles are flattened out at the surface of the core particle. The solder forms small dot-like islands, and they are isolated each other. Several applications of such kind of composite particles are described. Single particle device is a PTC thermistor, which consists of one composite particle of semiconducting BaTiO3. Flexible and self-thermostatic sheets can be produced by packing the composite particles between two thin electrodes. Using NTC particles instead of the semiconducting BaTiO3 single particle devices of NTC thermistor and flexible NTC sheets can be produced. Twin particles device is a combination of a single particle PTC thermistor and a single particle NTC thermistor in series, and will be a V-type thermistor, having both PTC and NTC properties. The V-type thermistor can be obtained also by stacking the layer of PTC composite particles and that of NTC composite particles in series. It can be applied to a protective device.
A metallic closed cellular material containing organic materials for the smart materials has been developed. Powder particles of polystyrene coated with a nickel-phosphorus alloy layer using electroless plating were pressed into green pellets and sintered at high temperatures. A metallic closed cellular material containing organic materials was then fabricated. The density of this metallic closed cellular material was measured. The density of this material is smaller than that of other structural metals. On the fabricated metallic closed cellular materials, compressive properties, Young's modulus and ultrasonic attenuation coefficient were measured. The compressive tests showed that this material has the different stress-strain curves among the specimens that have different thickness of the cell walls. Each stress-strain curve has a long plateau region, the sintering temperatures of the specimens affect the compressive strength of each specimen, and energy absorbing capacity is very high. Young's modulus of this material depends on the thickness of the cell walls and the sintering temperature. The attenuation coefficient of this material observed by ultrasonic measurement is very large. These results indicate that this metallic closed cellular material can be utilized as energy absorbing material and passive damping material.
We aim to fabricate microstructure and microdevices by integrating and arranging powder particles, i.e., the particle assemblage. We have developed three assembling techniques of the particles. The details of the assembling techniques and samples of the assembled microstructures are introduced. A manipulator is developed to manipulate and to weld metal particles by using a tungsten probe. Nickel alloy particles of 50 micrometers were piled on a gold substrate by the manipulator, and a leaning tower of the particles is fabricated. The array of the leaning tower is considered to act as an actuator. For the integration of a great number of particles, we developed another method based on the principle with the xerography. An electron beam or an ion beam is irradiated on an insulating substrate. An electrified pattern is formed on the substrate by the doped electron or doped ion. Fine particles are attracted to the pattern by the electrostatic force. Thus, we can arrange particles by immersing the substrate in the suspension of particles. The third is a productive method of ordered mixture by the electrostatic force. A self- thermostatic heater is made from the composite particles of BaTiO3 and In produced by the method.
We have developed a novel method for simple and quick fabrication of various 2D photonic crystals consisting o polymer rods arranged regularly in air using molds made by laser light. Square- and honeycomb-lattice photonic crystals, in which the radius of a rod, the spacing between nearest-neighbor rods, and the real part of a dielectric constant of the polymer were 22 micrometers , 90-100 micrometers and 3.7, respectively, were created, and far-IR transmission spectra were measured. The experimental and calculated result agreed with each other, indicating that our samples were genuine photonic crystals. In addition to well-known opaque regions in transmission spectra due to photonic band gaps and optical branches of uncoupled mode, we have discovered that the transmission is suppressed drastically at branches with flat dispersion due to the influence of absorption of light.
Probe manipulation of fine particles has been investigated in our laboratory. The feature of our system is that wide range of voltage, 0-10kV, can be applied between the probe and the substrate. In this method, we can pick up a fine particle at the tip of the probe, carry, place and weld the particle at a predetermined point on the substrate by controlling the applied voltage to the probe. When the particle is picked up, 10-50V is applied. And 2-10kV is applied for the welding. Breaking shear stress of welded particles is measured as follows. A sheet spring, where the strain gauges are stuck, is prepared. One end of the sheet spring is held, and moved to push off the welded particle by the free end. The shear stress is calculated from the output of the strain gauges. The breaking shear stress is 44-71MPa for gold particles welded on a gold substrate. Self- sustaining characters, 'NRIM', are formed from gold particles of 40micrometers as an example of microstructure. Preliminary experiments for the application to the ball grid array are carried out. We also fabricated a slant tower of magnetostrictive particles. It will be used as a micro- actuator in the alternative magnetic field.
Ausforming treatment can improve the shape memory effect of Fe-Mn-Si based shape memory alloys, however, the mechanism of this improvement is not so clear. In this paper, the influence of ausforming treatment on stress-induced martensitic transformation and its reverse transformation in an Fe-28Mn-6Si-5Cr shape memory alloy has been studied using atomic force microscope and TEM aiming to clarify the origin of this improvement. It was found that the ausforming treatment at 970K by 9 percent pre-straining, which is the optimum condition for improving shape memory recovery, can introduce many uniformly distributed stacking faults on the same slip plane in austenite. When an external stress is applied to such an ausformed specimen for shape change, uniformly distributed martensite bands with the same variant are produced in a grain due to the assistance of those preexisted stacking faults. When being heated over Af, these martensite bands are nearly completely reverse-transformed to parent phase through the same atomic pass as for the forward transformation, so a nearly perfect shape memory effect is obtained.
We propose a novel method to create various 3D arrangements of particles. In suspension such as an uncured polymer containing particles, the particles are aligned parallel to an imposed electric field, which are called particle chains, only on micro pillars of metal preformed at intended positions on a flat electrode due to an intensified electric field. The 2D arrangements of the 1D chains lead to the 3D arrangements of the particles. After the formation, the polymer is cured by heating in the electric field to stabilize the arrangements. According to this method, we succeed in making arrangements of glass beads with a diameter of 30 micrometers in silicone elastomer.
A new powder particle beam drawing apparatus is being developed in order to realize a solid free-form fabrication using a focused powder particle beam. The powder particle beam drawing apparatus was constructed of a powder particle injector, a powder particle beam gun, a beam deflector and focusing lenses. The powder particle injector supplies micro-sized powder particles of 0.1 to 100 micrometers gradually and continuously from a powder particle reservoir to a powder particle beam gun. The powder particle beam gun generates the beam of highly charged powder particles. The powder particles draws lines and figures on substrates through the beam deflector and focusing lenses. Preliminary experiments were carried out using carbon powder particles of 10 micrometers size. It was possible to focalize the beam size within 500 micrometers diameter and draw lines using the beam. These results suggests that the powder particle technology can be applied to fabrication processes of micro-electronics devices and micro-machines.
Five micrometers silica particles can be arranged on CaTiO3 substrates by drawing an electrified pattern on the substrate (drawing step) and then dipping it in a suspension of the particles (arranging step). The fixing treatment of the arranged particles is necessary in order to repeat the above two steps and to fabricate 3D micro-structures. A thin film of the fluoride polymer is formed on the substrate after the particle arrangement to fix the arranged particles. The effect of the coating film on the drawing step and arranging step was studied. It was found that the coating film improved both steps rather than cause interference. The drawing, arranging and fixing are the elemental techniques of the particle arrangement process, and 3D micro-structures can be constructed by repeating these steps in order. Application of the process to a gas sensor was discussed.
A new material for damping and energy-absorbing has been developed using a powder particle assembling technique. Powder particles of polystyrene coated with nickel-phosphorous alloy layers using electroless plating were assembled and sintered at high temperature. A closed cellular solid structure containing polystyrene was then constructed. The mechanical and ultrasonic properties of this cellular solid were measured at room temperature and at high temperatures. The compressive tests show that Young's modulus of this cellular solid is very small as are the changes due to increasing temperature, and the cellular solids have a high energy absorption. Ultrasonic measurement showed that the attenuation coefficient of this cellular solid is very large and would change due to increasing temperature. These results indicate that this cellular solid can be used for energy absorbing and passive damping systems.
In the previous paper, preliminary research results on powder particle assemblage technique using a microprobe was reported. It was shown that the technique makes it possible to manipulate powder particles one by one, etch microscopically and weld the powder particle into a substrate or other powder particles. In this work, the welding mechanism of this method and metallurgical properties of welded parts were investigated, and micro- actuators were fabricated by means of powder particle assemblage technique using the microprobe. The results indicated the potentiality of this technique for application to assemblage of micro-machine and micro-devices.
The purpose of the present work is to develop the materials with new functions by combining two kinds of particles electrified reciprocally. This paper reports a preparation method and the positive temperature coefficient of resistivity (PTCR) properties of complex particles consisting of semiconductive BaTiO3 granules and metallic indium powder particles. The conclusion obtained by the present experiment are as follows. (1) Vibrating cylindrical electrode can forced-electrify metal, semiconductor and insulator particles positively or negatively. (2) When the particles electrified reciprocally are mixed in the same region at the same time, complex particles can be created by the electrostatically attractive force working between the two kinds of particles. (3) Indium-semiconductive BaTiO3 complex particles made by this processing offer the new PTCR material which can be used in arbitrary shapes by filling and packing or drawing and painting.
A particle assembly using the electron beam was proposed as a process for creation of multi- functional and intelligent materials. Silica (SiO2) particles of 5.1 micrometers in diameter were arranged along the prescribed pattern on calcium titanate (CaTiO3) substrates as the first step on the particle assemblage. Latent electrified images were drawn on CaTiO3 substrates by scanning electron beam. The substrates were dipped in a suspension of SiO2 (dipping method) or the suspension was dripped on the higher end of the inclined substrates (dripping method). The SiO2 particles in the suspension were adhered on the latent image by electrostatic force. And the latent image was visualized as a image of particles arrangement. The images of particles arrangement were processed by an image analysis software. It was shown that the adhered particles can be represented by the normal distribution for the transversal direction to the electrified line, and the uniform distribution for the longitudinal direction. The sharpness of the images by particles was appraised by the above distribution model. It became quantitatively clear that the better images were obtained by the dipping method than by the dripping method.
Using a tungsten micro-probe with a tip of 2 micrometers radius, fine metallic powder particles could be manipulated one by one. By applying low voltage (about 10 V) between the probe and a metallic substrate, the powder particle on the substrate was adsorbed to the tip of probe easily, and by cutting off the voltage the powder particle was desorbed from the tip. Therefore it is possible to arrange powder particles as designed by controlling the voltage and movement of the probe. In addition to the powder particle manipulation, powder particles welding was studied. The tungsten micro-probe was contacted with the powder particle on the metallic substrate, and high voltage (about 10 kV) was applied between the probe and the substrate. It was observed that the glow discharge was caused between the powder particle and the substrate. The contacting parts of the powder particle and the substrate were melted and welded each other. By the manipulation and the welding, micro-structures composed of fine powder particles (about 60 micrometers ) were constructed. Powder particle towers and a micro- actuator were fabricated by way of trial. The results demonstrated the potential of the micro- probe assembly for the fabrication of electronic devices, micromachines and intelligent materials.
We proposed a particles assembling method to create intelligent and multi-functional materials. The arrangement of particles on substrates was studied as one of the important techniques for this approach. The arranging process is as follows. Electrified patterns were drawn on dielectric calcium titanate (CaTiO3) substrates with electron beam scanning. The substrates were dipped in a solvent where silica (SiO2) particles of 5.1 micrometers (phi) were dispersed. The particles were attracted to the electrified patterns by the electrostatic force, and were arranged along the electrified patterns. In this paper, undrawn substrates were used to know how many particles adhered on the unelectrified part, and then, arranging experiments using drawn substrates were carried out under various conditions to confirm the above process. We also discussed on the basic aspects of the arrangement, such as attraction force, motion of particles in the solvent, etc.
KEYWORDS: Moire patterns, Scanning electron microscopy, Electron beams, Copper, Fringe analysis, Electron beam lithography, Metals, Electron microscopes, Process modeling, Gold
Microcreep deformations in pure copper specimens are studied by a new moiré method. In this method, a fine micrograting prepared by electron beam lithography is used as a model grating, and a scanning exposure ofthe primary electron beam in a scanning electron microscope (SEM) as a master grating. The scanning exposure of the electron beam on the specimen with the model grating produces moiré fringes of bright and dark lines formed in response to the different amounts of the emitted secondary electrons for each primary electron. This new method makes it possible to obtain a clear and fine moiré fringe without an image-processing system and to observe the moiré fringe pattern and the SEM image at the same time. By this method, the inhomogeneous microcreep deformations such as grain boundary sliding, coarse slip, and localized strain are measured with high accuracy. It is confirmed that the creep strain is nonuniform even in the same grain and the strain distribution is caused mainly by the grain boundary sliding.
A new Moiré method using a scanning electron microscope (SEM) for the measurement of micro-deformation has been developed. This new method makes it possible to observe the Moiré fringe pattern and SEM image at the same time. In this method, a fine microgrid prepared by electron lithography is used as a model grid, and scanning exposure of the electron beam in a SEM as a master grid. The exposure of electron beam on the specimen with the model grid produces Moiré fringes of bright and dark lines formed by the different amount of the secondary electrons. This fine Moiré fringe pattern is fine and clear enough to measure the strain distribution in a small area. By this method, concentrated strains around a small holes in polyimide resin specimens and also the inhomogeneous micro-deformations such as grain boundary sliding in copper specimens were measured, with high accuracy.
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