Super High Temperature Research Articles

광중합에 의한 초고온 MEMS용 SiCN 미세구조물 제작과 그 특성

This paper describes the fabrication of SiCN microstructures for super-high temperature MEMS using photopolymerization of pre-ceramic polymer. In this work, polysilazane liquide as a precursor was deposited on Si wafers by spin coating, microstructured and solidificated by UV lithography, and removed from the substrate. The resulting solid polymer microstructures were cross-linked under HIP process and pyrolyzed to form a ceramic of withstanding over <TEX>$1400^{\circ}C$</TEX>. Finally, the fabricated SiCN microstructures were annealed at <TEX>$1400^{\circ}C$</TEX> in a nitrogen atmosphere. Mechanical characteristics of the SiCN microstructure with different fabrication process conditions were evaluated. The elastic modules, hardness and tensile strength of the SiC microstructure implemented under optimum process condtions are 94.5 GPa, 10.5 GPa and 11.7 N/min, respectively. Consequently, the SiCN microstructure proposed in this work is very suitable for super-high temperature MEMS application due to very simple fabrication process and the potential possiblity of sophisticated mulitlayer or 3D microstructures as well as its good mechanical properties.

Solidification characteristics of Tb 0.27Dy 0.73Fe x ( x = 1.8, 1.95) alloys during the directional solidification

Solidification characteristic of intermetallic compound is complex and dependent on its composition and the solidification conditions. Tb 0.27Dy 0.73Fe x ( x = 1.8, 1.95) alloy, as an intermetallic compound, exhibits different solidification behavior during its directional solidification. Experimental investigations of the behavior were carried in a super high temperature gradient directional solidification equipment developed by authors. The relationships between the solidification behavior and the solidification condition of Tb 0.27Dy 0.73Fe x ( x = 1.8, 1.95) alloys were determined. For Tb 0.27Dy 0.73Fe 1.8 alloy, solidification characteristics with short cylindrical, plate-like and mixed structure were exhibited under the different solidification conditions and zone with a plate-like structure is enlarged with the increase of the temperature gradient and the crystal growth velocity. For Tb 0.27Dy 0.73Fe 1.95 alloy, however, Terfenol-D crystal always grows with a plate-like structure in the experimental ranges. Plate-like structure zone is also enlarged with the increase of the crystal growth velocity and the temperature gradient. The experiment results are helpful for preparing an appropriate Terfenol-D crystal.

Preparation of a (Ti,Nb,W)C particulate reinforced nickel-base superalloy via super-high temperature treatment of melt

A well-dispersed (Ti,Nb,W)C particulate reinforced nickel-base superalloy was prepared via super-high temperature (above 2123 K) treatment of melt. Scanning electron microscope (SEM) observation and energy dispersive X-ray spectroscopy (EDS) results show that most of the (Ti,Nb,W)C particles have a carbonitride core. Gas analysis shows that nitrogen content in the alloy with super-high temperature treatment of melt is much higher than that in the conventional cast superalloy. The well-dispersed (Ti,Nb,W)C particles could be attributed that nitrogen combines with Ti in the alloy melt to produce TiN, which acts as the nucleator to form (Ti,Nb,W)C. This work provided a new way to prepare the TiC particulate strengthened composites.

Preparation of Terfenol-D with precise 〈110〉 orientation and observation of the oriented growth crystal morphology

In a super high temperature gradient directional solidification equipment developed by the authors, φ7 mm rare earth giant magnetostrictive rods with precise 〈110〉 orientations were manufactured successfully without any seed crystal. A dispersion of only 3° exists between the 〈110〉 oriented growth direction and the axis of the rod. During the directional solidification process, there exists a certain relationship between the crystal growth morphology and the crystalline orientation degree. The crystallites’ orientation degree can be determined conveniently through the observation of the crystal morphology. Under the condition of the temperature gradient of 800 K/cm and the withdrawal velocity of 6 μm/s∼10 μm/s, Tb 0.27Dy 0.73Fe 1.9 rod with 〈110〉 oriented crystals can be obtained when the solidified part of the rod reaches 20 mm. When the length of the solidified part is at least 30 mm, the 〈110〉 oriented crystallines can grow in a stable way.

Technique of melting and casting of (TbDy)Fe 2 matrix alloy bars

The technique of melting and casting rare earth giant magnetostrictive bars was investigated with super high temperature gradient directional solidification equipment developed by the authors. A number of φ7×120-mm bars with a smooth appearance were manufactured successfully; bars with different dimensions can be obtained by changing the molds. The results reveal that the fabrication process is available and simple. Under normal melting, the losses of Tb and Dy can be controlled to within 1 and 3%, respectively. The mean composition errors of the rare earth elements Tb and Dy are less than 1.5%. Metallographic examinations reveal that the microstructure is notably dependent on the mold temperature. In addition, the full process from melting and casting to directional solidification can be performed in the same equipment, and investment in facilities for melting and casting is not required.

High Volume Reduction and Group Separation of Simulated Fission Products by Cold Crucible.

An advanced technology of SHTM (Super High Temperature Treatment Method) using an induction cold crucible for the treatment of fission products generated after the reprocessing of spent fuel is proposed as the future stage of the current vitrification. Without adding any glass materials, 2000 g of simulated fission products consisting of 23 elements, including lanthanides oxides simulating highly active nuclides and corrosion products, together with the minimum amount of reducing agent were inductively heated up to 2000°C, followed by melting and solidification in a convergent type cold wall crucible. Internal diameter of the crucible, applied electric power and the frequency was 100 mm, less than 100 kW and 25 kHz, respectively. As a result, highly volume-reduced materials, approximately 1/20 of the current vitrification, was obtained. Platinum metal group, such as palladium and ruthenium, got together in the center and bottom of the crucible, surrounded with the titanium oxides immobilizing lanthanides elements. Validity of the process con-ceptwas confirmed experimentally. A cylindrical mathematical model with three phases coupled with electromagnetic field, heat conduction and mass balance has been developed to get better understanding of SHTM. The model predicts the presence of critical value of magnetic flux density and the initial dimension of the pretreated fission products that triggers the whole melting of the fission products in the crucible surrounded with the cold wall. Reaction free layer of fission products plays an important role for the melting. There exits an optimal intensity of the magnetic flux density sustaining high temperature of the material near the cold wall.

Super high electromechanical coupling and zero temperature coefficient surface acoustic wave substrates in KNbO/sub 3/ single crystal

The propagation characteristics of surface acoustic waves (SAW) and piezoelectric leaky surface waves in KNbO(3) single crystal have been investigated theoretically and experimentally. The results show that the electromechanical coupling coefficient k(2) of the surface wave propagating along the X-axis of the rotated Y-cut plate is very large with k(2)=0.53. This is about 10 times as large as that of LiNbO(3) in the surface wave branch. Experimental results for wideband SAW filters show low loss and temperature stable characteristics. The bandwidth is about 20%, and insertion losses are less than 2 to 6 dB. Simulation results for a ladder type filter using Y-cut KNbO(3) indicate that a bandwidth of 40% should be possible. The KNbO(3) substrates exhibit zero temperature coefficient of frequency (TCF) around 20 degrees C in rotated Y-cut substrates.

Investigation on the formation of the preferred orientations in a TbDyFe alloy with directional solidification

The formation of the preferred orientations in a TbDyFe alloy was studied by transmission electron microscopy (TEM). It was found that there were several different preferred orientations in the experimental TbDyFe alloy with directional solidification. 〈110〉, 〈112〉 and 〈113〉 preferred orientations were observed in this alloy solidified by our self-made super high gradient temperature directional solidification device. The preferred orientations changed with the variation of the solidification conditions. Two {111} twinning systems resulted in the 〈110〉 preferred orientation and a single {111} twinning system resulted in the 〈112〉 preferred orientation. The twinning displacement was observed and this formatted the 〈113〉 preferred orientation.

Rapid-Solidified Metallic Actuator Materials Developed by Electromagnetic Nozzleless Melt Spinning Method

AbstractElectro-magnetic nozzleless melt-spinning method was developed by combining the control of the flow down of the molten metals after electromagnetic float-melting(i.e. levitation) with rapid solidification by rotating roll. The metallurgical grain microstructures can be changed by rotating roll speed. It was confinned that the produced, intermetallic TiNi and NiAl system alloy thin plates showed the strong crystal anisotropy, higher shape memory functional properties than those of the conventionally processed melt-worked samples having its same origin. As new SMAs by using this method, ferromagnetic shape memory, FePd alloy having very large magnetostriction and super high temperature shape memory, RuTa alloy having the transformation over 1000°C were developed. Moreover, our recent study on the advanced rapid-solidification machine to produce many kinds of short fibers as well as ribbons is introduced. Finally, harmonic material design for sensor/actuator stacking composite system, namely “Smart Board” for aircraft structures will be introduced.

Magnetostriction of the Oriented Crystals in a TbDyFe Alloy

The preferred growth directions of Tb0.3Dy0.7Fe1.95 grown by a super-high temperature gradient zone melting directional solidification technique were examined over a large range of the crystal growth velocity (0.5-30 mm/min). The [110] preferred growth direction was found in most case, and the [112] orientation only existed with a certain solidification condition. The magnetostriction of the [110] oriented samples was poor and had no obvious "stress effect", which exists in [110] perfect crystals according to calculation. The difference of the magnetostriction between the actual and perfect [110] oriented crystal was discussed in detail. The poor magnetostriction of the [110] oriented samples was attributed to the special 109.5° angular with two (111) twin growth mechanism, which resulted in the [114] direction along axis in twins, and only the [110] along axis in master.

Analysis of thermal stress in a plate of functionally gradient material

Composite materials made of ceramics and metal are already used in heat resistant parts, such as pistons. Functionally gradient materials (FGM) are new composite materials that reduce the thermal stress caused by the difference of thermal expansion and that are resistant to super high temperature. In order to support the design of FGM, we have developed computer programs that analyze the transient heat transfer and the transient thermal stress of FGM by the finite element method (FEM). In this paper, the thermal stress analysis by these programs of an FGM plate, composed of Zr0 2 and Ti-6A1-4V, is discussed.

Ｎｂ‐Ａｌ合金粉末のＨＩＰ焼結体の機械的特性

Since Nb3Al has a high melting point and a low density, it is expected as a material of jet engine and the parts to be used at super high temperature. In this paper, the mechanical properties of HIP consolidations of Nb-Al alloy powder were studied.The compression strengths of HIPed and subsequently heat treated consolidation of Nb-Al alloy powder were higher than those of as-HIP one, because the powder boundary of as-HIP Nb-Al consolidation disappeared after heat treatment at temperature higher than 1873K and also the Nb3Al grain grew.The Nb3Al powder composites blended with Mo, W or a ceramic powder were also consolidated to improve high temperature strength. In the case of Nb3Al composites with Mo or W powder, the compression strength at high temperature were similar to those without Mo or W. On the other hand, the strengths of Nb3Al composites with ceramics were higher than those without ceramics. Especially, Nb3Al+Y2O3 consolidation showed 83MPa peak stress at 1973K.

Colour ferromagnetic state in SU (2) gauge theory at finite temperature

The explicit analytical expression for the one-loop finite temperature effective potential of SU (2) pure gauge theory in the presence of a uniform magnetic field and a background A 0 field is obtained. The high- and low-temperature limits are examined. The real part of the effective potential exhibits a nontrivial minimum at a finite value of the magnetic field strength. This minimum survives even at superhigh temperature thus including a sharp difference from the usual finite temperature Higgs model. For large enough values of the colour condensate A 0 field the imaginary part of the effective potential disappears. The role of the higher order leading infrared contributions is discussed.

Study of Processing Hllw by Super High Temperature Method. Part II*. Reducing Reactions and Formation of Complex Oxides in the Simplified Hllw

AbstractThe reducing reactions of platinum metal oxides and the formation of the complex oxides were studied to estimate the process at high temperatures. Heat treatment of Re207 with TiN causes reduction up to the sublimation point of Re207 and exhibits the highest value of the recovery among the reducing agents used in the present study. Reducing reactions of the platinum metal oxides with the reducing agents lower the melting temperature. The simplified complex oxides contain the complex oxides of the representative elements of FP and the metallic elements of the reducing agents, which contribute to a decrease of melting temperature, neodymium zirconium oxides and neodymium barium oxide which may transform to the other phases during heating. Uranium may dissolve in the phases in which uranium is identified by EPMA but cannot detected by X-ray diffraction.

An explanation for the solar neutrino problem

A new mechanism of thermonuclear reaction is briefly introduced. It shows that a certain amount of thermonuclear reaction can take place in dense, low-temperature (T < 1 × 105 K) plasmas. At a super-high temperature, it is in agreement with the old thermonuclear reaction mechanism first presented by Gamow and Bethe. As most regions in the Sun are at moderate and low temperature, a sufficient amount of fusion energy is generated therein. Therefore the solar central temperature in standard models must be decreased to about 13.8 × 106 K. That would make the flux of high-energy neutrinos conform with the observational results.

Database for super high temperature materials under severe environment

A property database management system of high-performance materials for severe environments is being developed. The types of the high-performance materials include inter- metallic compounds and advanced composites such as carbon/carbon and SiC/intemetallic compound composites. The database system is composed of personal computers and has a computer network connecting governmental institutes, industrial companies and several universities for data input and output. The construction of the database system, the data formats, the testing methods for material properties, the management of the system, the property data of high-performance materials, and the statistical aspects of the data are investigated.

SOME NEW ASPECTS OF SUPER-HIGH TEMPERATURE SUPERCONDUCTORS

We review some salient features of the recently observed experimental evidence of ceramic super-high temperature superconductivity (T c &gt; 200 K ). Two theoretical estimates which are capable of accounting for super-high T c will be presented. For comparison, several reports on non-ceramic oxide super-high temperature superconductors will also be discussed.

HIGH TEMPERATURE SUPERCONDUCTIVITY AND COLD FUSION

There are numerous historical and scientific parallels between high temperature superconductivity (HTSC) and the newly emerging field of cold fusion (CF). Just as the charge carrier effective mass plays an important role in SC, the deuteron effective mass may play a vital role in CF. A new theory including effects of proximity, electron shielding, and decreased effective mass of the fusing nuclei can account for the reported CF results. A quantum-gas model that covers the range from low temperature to superhigh temperature SC indicates an increased T c with reduced dimensionality. A reduced dimensionality effect may also enhance CF. A relation is shown between CF and the significant cluster-impact fusion experiments.

Phase and superconductivity of SrBaYCuFO system

The superconductivity and phases of SrBaYCuFO system are studied. The superconducting critical temperature T c, of this system is about 85K. When more SrCO 3 is added into the SrBaYCu 3F 2O 6, the 1–2–3-like phase is formed whose superconductivity is quite different from that of multiphase SrBaYCuFO system, and this phase may be responsible for the superhigh temperature superconductivity of 105K.

Study on the super high pressure and high temperature apparatus

Study on the super high pressure and high temperature apparatus