摘要:

Thermochemical analyses are performed for the Ti–O–C, Fe–O–C, Al–O–C, Si–O–C, Mg–O–C, Be–O–C, Y–O–C, Cr–O–C, and U–O–C systems at 1800 K. The role of hydrogen, water vapor, and nitrogen in connection with these systems is exemplified. LogpMexOyvs logpO2and logpCvs logpO2diagrams are prepared to illustrate in a simple manner the relations between condensed phases and the equilibrium pressures of gaseous species over the different condensed phases. The diagrams are used to evaluate the correctness or applicability of available thermochemical data, and to predict or interpret reactions in or between the different systems, with particular reference to vacuum metallurgical processes.

ISSN:0022-5355    

DOI:10.1116/1.1315922

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

A brief review of the theoretical and experimental work on the kinetics of the vacuum degassing of liquid metals is given. This review is limited to the case usually encountered where the transport in the melt alone is rated determining, i.e., where desorption processes at the melt surface and the transport in the gas phase may be neglected. Different models describing the mass transfer from the interior of the melt to the interface are also discussed. The course of degassing of a melt pool without bubble formation, based on the mathematical treatments of Kraus (see Refs. 1 and 2) and Machlin (see Ref. 3) is described. In the model of Kraus—which may be applied, for instance, to ladle degassing—convection currents in the interior of the melt develop by density differences caused by the heat loss of the freely radiating melt surface. The calculations of Machlin refer to inductively stirred melts. Formulas for the mass transfer coefficients for these two cases are given. If layers of surface active elements or slags accumulate at a melt surface, the rate of degassing may be largely reduced. There is also an examination of how far the model of Kraus is applicable to degassing in electron-beam and vacuum-arc melting with consumable electrodes. Most technical degassing processes rely on the formation of bubbles, for only with them are the high rates required for economical degassing obtained. Also shown are the conditions under which bubble nuclei may exist and growth of the bubbles in a melt pool or in stream degassing is possible. Reference is made to the calculations of the gas pick-up of ascending CO bubbles in a steel melt made by Kraus (see Refs. 1 and 2), which also permit the calculation of the mass transfer coefficient if, in this case, a surplus of nuclei in the melt exists. If the gas content is too low for spontaneous bubble nucleation, the use of a neutral scavenging gas is advantageous. Computations of its purging effect have been made by Bradshaw and Richardson (see Ref. 4) as well as by Lange et al. (see Ref. 5). Stream degassing is not accessible to an exact mathematical treatment. However, an estimation of the degassing rates of droplets and experimental results show that the removal of hydrogen probably takes place mainly by diffusion from the external surfaces of metal droplets and bubbles, whereas nitrogen and oxygen removal depends more on the bubble formation in the metal stream and melt pool.

ISSN:0022-5355    

DOI:10.1116/1.1315905

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

Continuous electron-beam evaporation of binary alloys was studied. Silver-copper wires with 5, 10, 20, and 30 at.% of silver were fed into an evaporation source which was heated by an electron beam. Beam powers up to 4.5 kW were used and evaporation temperatures from 1625–1960 K were obtained. Methods were developed to study mass and composition distribution of the vapor flux, the transient period, and the steady-state conditions. Prediction of the transient and the steady-state relationships among the compositions of the feed wire, the evaporant bath, and the vapor deposit, based on (a) published thermodynamic properties of silver-copper alloys, and (b) the assumption that the Langmuir equation correctly relates the evaporation rate of a particular component from solution to the equilibrium partial pressure of that component, agrees closely with experimental results. This means that transport within the liquid phase by diffusion or convection is not a significant rate-controlling factor.

ISSN:0022-5355    

DOI:10.1116/1.1315912

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

The role of computers in applied research is discussed. Computer simulation is considered as a new set of mathematical techniques which augments and goes beyond the older analytic techniques. The major challenge of simulation methods is scientific rather than computational in the selection of models to represent a physical process. Models are discussed in the context of the problems of applied science. The simulation approach differs from conventional methods in that several models are combined to represent the one physical process. The role of the computer is to fit the models together in an interactive ensemble. Simulation techniques are exemplified first by a simulation of the bending and fracture of a Charpy impact specimen. The simple simulation is shown to be a powerful technique for automatically analyzing the data output from an automated test system. Two applications of simulation techniques to solidification processes are next described. The first deals with dendrite growth. A computer simulation shows that models for heat (or solute) flow coupled with a model for the solid-liquid interface are adequate to account for the branching and growth velocity of dendrites. The second deals with a solidifying casting aud illustrates the way additional models can be added to allow the description given by the simulation to resolve finer details of behavior. The wide scope of simulation techniques is illustrated by reference to the simulation of transmission electron micrographs. In conclusion, the sequential approach to simulation is recommended. In this approach, the simplest possible simulation is developed first. Then, additional models are added to refine the original treatment and improve its resolution.

ISSN:0022-5355    

DOI:10.1116/1.1315913

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

This paper describes a semicontinuous heat treatment equipment with some of its operating results for metal strips or foils. Work accelerated electron flux from a hot hollow cathode discharge is used for bombarding the strip. Use of hot hollow cathod discharge for annealing of a metal strip was briefly discussed by Morley in 1963. (see Ref. 1.) Smith, Jr. and Hunt reported in 1965 (Ref. 2) the use of high-voltage high-vacuum electron beam for continuous annealing of metal strips. Homogeneous thermal history, rapid heating cycle, and a very high temperature processing are obtainable by using an electron bombardment heating for running strips. Processing of metal strips while running will also be desirable for high temperature treatment where adhesion between layers of a roll may cause defects. The high-voltage high-vacuum EB is advantageous in obtaining higher energy density than the use of hot hollow cathode EB. The latter, however, operates at a low voltage and often more economically than the former. Less evaporation of a volatile component can be another factor to be considered for some alloys. Thus refractory alloys strip rolls that require high temperature contamination free environment, minimum vaporization of volatile component, and nonsticking between layers will be suitable for the plasma EB semicontinuous or continuous processing.

ISSN:0022-5355    

DOI:10.1116/1.1315914

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

The advantages of electron-beam melting and casting compared to vacuum arc casting techniques will be discussed. The relations between fluidity, superheat, mold material, and mold temperature will be demonstrated using cast stars. Essential mechanical and chemical properties of cast rod samples will also be discussed. Process data of an electron-beam investment casting furnace such as beam power, casting production, and attainable superheat will be correlated. Results of a newly developed pelletizing process for titanium-scrap recycling and the purification of tungsten carbide particles illustrating the influence of pellet shape, gas content, and pellet weight will be discussed and compared to another, but different, recycling process for scrap consolidation by electron-beam melting. Use of the electron-beam continuous flow melting process for the production of long and thin titanium and steel castings will be demonstrated. The possibility of using scrap as starting material will be illustrated and compared with other types of starting stock.

ISSN:0022-5355    

DOI:10.1116/1.1315916

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

Liquid binary alloy targets have been sputtered at ion densities of up to100 W/cm2providing deposition rates in excess of 10 mils/h in a combined sputtering-evaporation mode. At high power densities a serf-sputtering mode has been demonstrated which allows deposition from10−7to10−2Torr. Comparison of sputtered deposit compositions of Pb-24 In, Fe-30 V and Fe-32 Ni with theoretical molar ratios predicted on the basis of thermal vaporization shows that alloy fractionation is substantially reduced. The composition of deposits from solid or liquid Pb-24 In targets had nearly the same Pb/In ratio,5.8 (target ratio= 1.75)although the predicted ratio for thermalized vapor was 1300. For Fe-30 V liquid targets where less than 0.5% vanadium is predicted from thermal vaporization alone, a sputtered deposit containing 10.3% vanadium was found, suggesting that the approximate sputtering/evaporation ratio is 0.3. Liquid phase targets of Fe-32 Ni alloy had average molar ratios of Fe/Ni close to 3 (target ratio was 2.2), whereas the predicted ratio from thermal vaporization was 5.8. There was only a slight increase in Fe/Ni ratio in the self-sputtering mode at10−6Torr over that obtained with argon sputtering at10−3Torr.

ISSN:0022-5355    

DOI:10.1116/1.1315917

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

Thin films of the superconducting compound niobium nitride were deposited at atmospheric pressure on fused silica substrates by reaction of gaseous niobium pentachloride with ammonia and hydrogen gases in a fused silica apparatus. Suitable conditions for the preparation of NbN were found by calculating the free energies of reaction for several possible reactions involving niobium chlorides, ammonia, and hydrogen. Niobium nitride films could be formed at substrate temperature ranging from 900°–1000°C. The deposition rate varied with the reaction conditions from 20 to 1500 Å/sec, and deposits ranged from smooth films of polycrystals in which the individual crystal faces were 20 μ in length. The x-ray diffraction data for the NbN films deposited at 1000°C revealed face-centered cubic structure with cube edge of about 4.358 Å. Niobium nitride films prepared by this method had a wide range of resistivities, temperature coefficients of resistance, and superconducting transition temperatures depending on the deposition conditions. The maximum transition temperature obtained was 15.75 K for the films deposited at 900°C.

ISSN:0022-5355    

DOI:10.1116/1.1315918

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

The supersonic titanium aircraft has requirements for high-strength titanium-alloy foil for honeycomb structures. In conventional rolling of such alloys as titanium-6% aluminum-4% vanadium, multiple high-vacuum anneals are required to reach the thin-foil gages, from 0.001–0.004 in., used for honeycomb cores. The advantages of electron-beam evaporation and deposition in the desired thicknesses, and without rolling and multiple vacuum annealing, are studied. The present research program is designed to prove that foils of such alloys, produced by EB evaporation on a moving substrate, are equivalent to the rolled products. EB foils easily meet the chemical and mechanical property requirements of aerospace specifications. Bend tests are superior to the rolled foil. The metallurgical characteristics have been evaluated using optical micrography and electron micrography with replica, transmission, and scanning techniques. The deposits are fully dense and of grain sizes from 0.2–0.8 μ. Microprobe analyses indicate that the chemical composition is uniform and contains alpha and beta phases. All metallurgical characteristics of EB evaporated foils appear to be suitable for the intended end uses. Evaluations in the form of actual honeycomb structures are underway.

ISSN:0022-5355    

DOI:10.1116/1.1315919

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

A system for zinc vapor generation and deposition onto a strip substrate at high rates is described. A resistance heated graphite crucible with a special design to suppress uncontrolled boiling is able to produce zinc vapor outputs as high as 150 lb/h for the300 in.2hearth area utilized. An efficient system for nozzling the zinc vapor onto the strip substrate from an enclosed hood allows this maximum vaporization rate to be condensed uniformly at a thickness of 0.6 mils across a 12-in. width at a line speed of 100 ft/min. Control of the vaporization rate is obtained through variation in the power input according to a heat flow model and also by means of a barometric liquid-zinc leg which is used to fill and empty the crucible and feed it continuously from outside the vacuum chamber. Other methods used to control the system are also discussed briefly as is the type of coating produced by deposition at these high rates.

ISSN:0022-5355    

DOI:10.1116/1.1315920

出版商:American Vacuum Society    

年代:1970

数据来源: AIP