Low-volume-fraction particulate preforms for making metal-matrix composites by liquid metal infiltration

A preform technology for making particulate metal-matrix composites with a low particulate volume fraction (as low as 18%) by liquid metal infiltration is provided. This technology used a non-combustible reinforcement (SiC) as the primary particulate and combustible particles (carbon) as the secondary particulate in the preform. The secondary particulate was removed from the preform by oxidation prior to liquid metal infiltration.     

Doping of optical fiber preforms via porous silica layer infiltration with salt solutions

A process is described for reproducible deposition of porous layers uniform along the preform axis, and the effect of the nature of the solvent on the infiltration of salt solutions into the porous layer is analyzed in relation to the fabrication of fiber preforms with controlled doping level. Data are presented on the variation of the retention volume in the porous layer with sintering temperature.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 363–368.Original Russian Text Copyright © 2005 by Khopin, Umnikov, Guryanov, Bubnov, Senatorov, Dianov.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Thermoprobe method of measuring the temperature of molten metal and the difference between metal temperature and crystallization point

The authors propose a method of measuring T_m and T_s=t_m–T_cr based on the laws of heat transfer between a cooled wall and molten metal.     

Fatigue crack growth rates in a porous metal

Fatigue crack growth rates were studied in A1S1 4600 alloy steel containing various levels of porosity. The materials used for the study were prepared using powder metallurgical techniques, with porosity content controlled by hot press-forging of sintered billets. Growth rates of fatigue cracks were found, when fitted to a simple power law in stress intensity range, to exhibit two distinct response patterns. When the cyclic plastic zone size was less than, or roughly equal to, the average pore diameter, growth rates were governed by relatively large exponents. For larger values of the stress intensity range, and correspondingly larger plastic zones, the growth rate exponent was reduced. The larger zone sizes were found to be equivalent to the average interpore spacing. The implications of varying crack growth rates on design and failure analysis of porosity-prone structures are discussed.     

Fabrication of short carbon fiber preforms coated with pyrocarbon/SiC for liquid metal infiltration

A novel method of fabricating short carbon fiber preforms was proposed for liquid metal infiltration. The preforms were shaped by wet forming and strengthened by pyrocarbon (PyC). SiC layers were prepared on carbon fibers by the reaction of SiO and PyC at 1600 °C. X-ray Diffraction, Scanning Electron Microscopy, and Energy Dispersive X-ray Spectroscopy were applied in the characterization of the preforms. Gas pressure infiltration was done to demonstrate the feasibility of the preforms for the liquid metal infiltration. The microstructure analysis indicates that carbon fibers are uniformly distributed in the preforms, and fibers are coated with an inner layer of PyC and an outer layer of SiC. The infiltration experiment proves that the prepared preforms are feasible for liquid metal infiltration under low infiltration pressure and temperature.     

A new method of measuring the snow-surface temperature

Because a snow cover is so tenuous, measuring its surface temperature is not easy. The surface is illdefined and easily disturbed; invasive transducers commonly used for other surfaces are, thus, generally inappropriate for snow. We therefore describe a hygrometric method of measuring the snow-surface temperature. The advantages are that the method is non-invasive, that its accuracy depends only weakly on the surface structure, and that it is reliable even in bright sunlight. The key assumption is that the air at a snow surface is in saturation with the snow; the dew-point temperature of air right at the snow surface is thus the surface temperature. Consequently, under a fairly wide range of conditions we can, in effect, measure the surface temperature by measuring the dew-point temperature 10 cm above the surface. We develop a theoretical justification for the hygrometric measurement, discuss the meteorological parameters that affect the accuracy of the method, and compare hygrometer data with more traditional measurements.     

Photoemission method of measuring temperature

A photoemission method of measuring temperature is presented, and the range of its application is indicated. Expressions are obtained for calculating the systematic error, and a nomogram is given for determining it.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 2, pp. 257–265, August, 1978.     

A high temperature high purity source for metal beam epitaxy

We report the first use of modulated beam mass spectrometry to assess the purity of metal beams generated from two types of Knudsen effusion oven used in metal beam epitaxy. One of these types contained sapphire components in contact with tantalum heater windings. In this case considerable contamination of gold and silver beams by Al₂O and aluminum was observed over the temperature range 1000–1400°C. Thermodynamic considerations support the view that these contaminants originated from contact reduction of the sapphire by the tantalum metal. The condensation of these impurities on an (001) indium phosphide surface at not greater than 40°C was detected by Auger electron spectroscopy.In the second type of oven all oxide components were replaced by pyrolytic boron nitride and the tantalum windings by molybdenum windings. Gold and silver beams generated from this oven were of high purity with no detectable oxide species or other beam contaminants. Aluminium beams contained Al₂O as a transitory beam impurity due to atmospheric oxidation of the aluminium charge prior to loading.The implications of the beam impurities from the first type of source are discussed, and the performance of the second type of source in generating epitaxial silver, aluminium and gold films on indium phosphide at growth temperatures not greater than 40°C is reviewed.     

Dynamic tensile deformation and fracture of metal cylinders at high strain rates

An experimental study has been presented on the radial deformation of aluminium and copper cylinders of internal diameter 52 mm and wall thickness 1–7 mm, internally loaded with high explosives. High speed photography and flash radiography have been employed to record the distance–time (x–t) history of the cylinder wall, which has been found to expand under strain rates of 10⁴–10⁵ s⁻¹. The rupture of the cylinder is identified by the leakage of detonation gases, through the cracks in the cylinder wall. Rupture strains of 70–160% have been found for commercially pure aluminium. For a fixed wall thickness, the rupture strain increases with the strain rate. However, when the cylinder wall thickness is changed, a maximum is observed in a graph showing the strain and strain rate relationship. Aluminium appears to follow the Ivanov rupture criteria. From the experimental data the macroscopic viscosity coefficient for aluminium has been found to be 0.55–0.87×10³ Pa s. In the deformation of a copper cylinder the cracks initiate at strains of 30–60%, followed by rupture at very high strains up to 300%. The crack propagation velocity through the copper cylinder wall has been found to be 250–300 m/s. Recovered fragments show wall thinning by 50–60% and also exhibit shear fracture which dominates the radial fracture in high velocity deformation of the metal cylinder.     

Wetting in infiltration of alumina particle preforms with molten copper

The high-temperature wettability of alumina particulate preforms by copper is investigated by means of infiltration experiments conducted at 1473 K under low oxygen partial pressure. Wetting is quantified in terms of drainage curves, which plot the volume fraction of metal in the porous medium vs. the applied pressure. Mercury porosimetry is also used on similar preforms for comparison. The effect of volume fraction, particle geometry and capillary parameters on the drainage curve are studied and compared with the expression proposed by Brooks and Corey. The influence of the particle volume fraction and capillary parameters characterizing wetting in the two systems is discussed to derive an effective contact angle for wetting of alumina particles by molten copper.     

A method of measuring electrode temperature for arc powercalculation

A technique for the construction of the thermocouple probe used for the measurement of electrode temperature under the influence of arcing in a low-power circuit breaker at break is reported. The problem of appreciable heat diffusion to the surroundings during the short time of arcing at break, typically 3-6 ms (depending on the speed of break), is dealt with by placing the thermocouple probe as near as possible to the electrode's surface, and in the center where, in most cases, the arc occurs. Under dc test conditions the amounts of the are power received by each electrode for various parameters such as current and electrode spacing are calculated     

Processing of Al2O3/SiC ceramic cake preforms and their liquid Al metal infiltration

In order to prepare ceramic preforms, chemical processes were used rather than using mixing of ceramic powders to obtain porous Al₂O₃/SiC ceramic foams. A slurry was prepared by mixing aluminium sulphate and ammonium sulphate in the water, and silicon carbide powder was added into the slurry so that a uniform mixture of Al₂O₃/SiC cake could be produced. The resulting product was (NH₄)₂SO₄·Al₂(SO₄)₃·24H₂O plus silicon carbide particles (SiC_p) after dissolving chemicals in the water. This product was heated up in a ceramic crucible in the furnace. With the effect of heat it foamed and Al₂O₃/SiC cake was obtained. Resulting Al₂O₃ grains were arranged in a 3D honeycomb structure and the SiC particles were surrounded by the alumina grains. Consequently, homogeneous powder mixing and porosity distribution were obtained within the cake. The morphology of the powder connections was networking with flake like particles. These alumina particles resulted in large amounts of porosity which was desired for ceramic preforms to allow liquid metal flow during infiltration. The resulting high porous ceramic cake (preform) was placed in a sealed die and liquid aluminium was infiltrated by Ar pressure. The infiltration was achieved successfully and microstructures of the composites were examined.     

多孔金属材料高温吸声性能测试及研究

以多孔金属材料在高温环境下的吸声特性研究为背景,以不锈钢纤维烧结型多孔金属材料为主要研究对象,首先在理论上研究了计算多孔材料吸声特性随温度变化的特性,然后设计并研制了一种温度可控的高温阻抗管测量装置。通过实验测试,获得了具有不同声学参数的金属纤维板在不同环境温度下的吸声系数,研究了温度对其吸声性能的影响规律。理论结果与实验结果基本吻合,证明了理论分析以及实验装置设计的合理性。     

A method for measuring strip temperature in the steel industry

In the steel industry, there are many processes that include measuring and control of temperatures. With higher demand on quality, increased production, and effective energy consumption, the use of noncontact temperature measuring techniques has increased. After the cooling section in a continuous annealing-pickling line, the strip temperature is estimated by using the grey box technique. Temperatures are measured in the cavity between the strip and the roller using radiation thermometers. A model is made for estimating strip temperature using the measured temperatures and knowledge of the physics of the process.     

Direct measurement of drainage curves in infiltration of SiC particle preforms

Drainage curves (plots of the non-wetting fluid saturation versus applied pressure) for infiltration of SiC particle preforms with Al and Al–12.2 at.% Si are measured at 1023 K (750 °C) with a pressure infiltration apparatus adapted for direct tracking of the metal ingress into the porous preform. From these curves the work of immersion is estimated by integration over the whole range of saturation and pressures from 0.1 MPa to 10 MPa, which in turn is used to deduce the metal contact angle on the ceramic. Drainage curves obtained for powder beds based on monomodal SiC particles of mean diameter from 6.5 μm to 40 μm yield values for the work of immersion and contact angles that are consistent among themselves and are in good agreement with data in the literature determined by the sessile drop method.     

Facing targets type of sputtering method for deposition of magnetic metal films at low temperature and high rate

A new type of cathode sputtering apparatus with two targets facing each other has been developed to prepare magnetic films at a high deposition rate without the extreme rise of the substrate temperature. When two disks of iron and nickel were used as targets, the maximum deposition rates obtained were approximately 4000 and 5000 Å/min, respectively. The substrate temperature was not elevated above 200°C during sputtering. The high rate deposition of Mo permalloy films also was attempted by co-sputtering of two facing targets composed of disks of iron and nickel and chips of molybdenum. The Vicker's hardness of the obtained Mo permalloy films was about 900 and the typical values of permeability at 1 MHz magnetic field and coercive force at dc magnetic field of them were about 2500 and 0.16 Oe, respectively.     

Fabrication and squeeze casting infiltration of graphite/alumina preforms

The manufacturing of a suitable rigid porous graphite/alumina preform has been investigated taking into account the influence of the binder type, the graphite/alumina content in the preform and the percentage of binder in water. The preforms showing an acceptable rigidity have been infiltrated with a CuSn12 bronze alloy by squeeze casting considering two different pouring temperatures. The composite quality is strongly influenced by both the graphite/alumina volume fractions and the binder type. The optimal quality has been obtained by infiltrating a Carsil 2000^TM binded preform containing 30 vol % graphite flakes and 70 vol % alumina fibres.     

Dynamic method of measuring the thermal conductivity of gases at high temperatures

The author proposes a method of measuring and a formula for calculating the thermal conductivity of gases during monotonic heating.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 5, pp. 850–858, May, 1972.     

Pressure-pulsed chemical vapour infiltration of TiN to SiC particulate preforms

SiC particulate preforms were infiltrated by TiN matrix from a gas mixture of TiCl₄ (5%), nitrogen (30%) and hydrogen using a repeating pressure pulse between 760 and about 1 torr. SiC particle sizes of 5 and 20 m were used. For matrix packing into deep level, optimum temperature was determined between 800 and 850 °C, and the maximum packing ratio reached 67% after 4 × 10⁴ pulses at 850 °C. The increase of TiCl⁴ concentration to 10% resulted in higher deposition rate and packing ratio. The decrease of nitrogen concentration led to slower deposition, that is, a similar effect to temperature lowering. The maximum flexural strength measured was 140 MPa.