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Nov 1971

Volume 8, Issue 6, pp. VM5-758


Effects of Some High-Voltage Conditioning Processes on Tungsten Electrodes

J. J. Maley

J. Vac. Sci. Technol. 8, 697 (1971); http://dx.doi.org/10.1116/1.1315379 (4 pages) | Cited 5 times

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The effects of electrical, gas, and heat conditioning on the physical characteristics of projections, or whiskers, on tungsten electrodes have been investigated. The use of a cylindrical projection tube to obtain current-voltage characteristics and the interpretation of this data by Fowler-Nordheim plots has lead to a better understanding of physical processes occurring at the cathode during high-voltage conditioning processes. It was found that typical surface parameters, such as, emitting area, field enhancement, critical breakdown field, and the number of whiskers on the cathode vary considerably, depending on the type of conditioning the cathode received.
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85.45.Bz Vacuum microelectronic device characterization, design, and modeling

Detailed Calculations of the Number of Distinct Sites Visited in Random Walk on Several Two-Dimensional Substrate Lattices

D. J. Pocker and S. J. Hruska

J. Vac. Sci. Technol. 8, 700 (1971); http://dx.doi.org/10.1116/1.1315380 (8 pages) | Cited 3 times

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Calculations of the number of distinct sites visited in random walk on six physically different substrate lattices are carried out with exact, Monte Carlo and approximate analytical techniques. The fraction, λ, of the total possible sites, m, which are distinct is tabulated and plotted for all useful m for four lattice geometries and for 10≤m≤1000 for two more. The validity of this single valued characterization is examined and found to be very good, especially for larger m. Plots of parameters for functional application of the results are given.
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05.40.Fb Random walks and Levy flights

Saturation Density of Stable Clusters in Thin Solid Films: Random-Walk Corrections

D. J. Pocker and S. J. Hruska

J. Vac. Sci. Technol. 8, 708 (1971); http://dx.doi.org/10.1116/1.1315381 (6 pages)

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Expressions for the saturation density of stable solid clusters, as formulated by Lewis and Campbell, are considered and modified. Consideration of the path behavior of randomly migrating monomer shows that the size of trapping areas is reduced by a factor of 10 in typical cases. Computational methods are illustrated to facilitate calculation of desorption and migration activation energies from saturation density data.
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81.15.Aa Theory and models of film growth
05.40.Fb Random walks and Levy flights

Two-Layer Approach in Making Insulating Films Less Than 100 Å Thick

E. J. Hsieh

J. Vac. Sci. Technol. 8, 714 (1971); http://dx.doi.org/10.1116/1.1315382 (4 pages)

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The merit of making very thin insulating layers less than 100 Å thick, by successively forming two layers of different dielectric films, was evaluated. The basic test structure was a capacitor with its insulating layer made up of different thickness combinations of thermally grown Al2O3 and vacuum-evaporated SiO. The two-layer dielectric films always give superior yields. In general, the result seems to indicate that a thinner insulating layer can be made from two layers of different dielectric films than from a single layer of either material.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
77.55.-g Dielectric thin films

A Simple Classical Model for Trapping in Gas–Surface Interactions

W. H. Weinberg and R. P. Merrill

J. Vac. Sci. Technol. 8, 718 (1971); http://dx.doi.org/10.1116/1.1315383 (7 pages) | Cited 20 times

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A simple model based on an assumed attractive square well and impulsive repulsive potential is developed to enable the calculation of initial trapping probabilities from thermal accommodation coefficient data. The gas species impinge on a smooth solid surface and are considered to be trapped if they transfer enough energy to the solid to fall into the interatomic potential well. The amount of energy transfer is determined by empirical values of the thermal accommodation coefficient. The model predicts the correct trends with surface and gas temperature when compared with rare gas scattering data and gives values accurate within a factor of 2 or better. Agreement between the model calculations and the sticking coefficient for deuterium adsorption on platinum is also found.
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34.35.+a Interactions of atoms and molecules with surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Deposition and Detection of Ag and Au Films Below 0.01 Monolayer

Marianne E. Behrndt

J. Vac. Sci. Technol. 8, 724 (1971); http://dx.doi.org/10.1116/1.1315384 (9 pages) | Cited 2 times

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The controlled deposition of extremely small amounts of Ag and Au is described. A shutter arrangement was developed which permits the deposition of metals from 10−3 monolayer upwards, in conjunction with a rate-controlled evaporation source. Either continuous or stepwise variation of film thickness was attained. Deposits below about 1 monolayer consisted of particles which were invisible ill the electron microscope. Their presence was detected by subsequent amplification of their size such that a visible deposit was formed. This was accomplished either by physical development, as known in photographic chemistry, or by vacuum deposition of zinc which was nucleated by these particles. The detection sensitivity of the methods is compared.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Auger Electron Energies (0–2000 eV) for Elements of Atomic Number 5–103

R. N. Yasko and R. D. Whitmoyer

J. Vac. Sci. Technol. 8, 733 (1971); http://dx.doi.org/10.1116/1.1315385 (5 pages) | Cited 1 time

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Auger electron energies for elements of atomic number 5 to 103 have been calculated using the atomic energy level values of Siegbahn et al., and a system of programs. The Auger electron energy table provides a listing of the element, the Auger transition, and all the calculated energies in ascending order from 0 to 2000 eV. These data are in the range of interest to Auger electron spectroscopists involved in surface studies.
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32.80.Hd Auger effect (including Coster-Krönig transitions)

Pressure Considerations Associated with Ion Sampling from Glow Discharges

J. W. Coburn and Eric Kay

J. Vac. Sci. Technol. 8, 738 (1971); http://dx.doi.org/10.1116/1.1315386 (6 pages) | Cited 27 times

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A discussion is presented of the influence of ion-neutral collisions downstream from an orifice through which ions from a glow discharge are being extracted. The effective pressure on the low pressure side of the orifice is treated as the sum of a static pressure (determined from pumping speed and orifice conductance considerations) and a localized beam pressure which is due to the neutral species effusing through the orifice with the ions. It is shown that in most experimental situations the beam pressure has a much greater influence on a collimated ion beam than does the static pressure. Some experimental results which support this conclusion are presented.
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52.70.Nc Particle measurements
52.80.Hc Glow; corona

Physisorption of Ar, Kr, CH4, and N2 on 304 Stainless Steel at Very Low Pressures

M. Troy and J. P. Wightman

J. Vac. Sci. Technol. 8, 743 (1971); http://dx.doi.org/10.1116/1.1315387 (8 pages) | Cited 2 times

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Physisorption isotherms have been measured for argon, krypton, methane, and nitrogen on 304 stainless steel in the temperature range 77–90 K and in the pressure range 10−9−10−4 Torr. A static technique was used to obtain the isotherms whereby the pressure change of the test gas in a constant-volume system was measured on immersion of the commercially available 304 stainless-steel nipple in different cryogenic baths. The ionization gauge was operated at reduced emission current (25–40 μA) to minimize gauge pumping. Adsorption measurements were made at two positions on the nipple and then subtracted to give an isotherm for adsorption on a geometric area of 47.5 cm2. This difference technique was used to minimize the effect of a measured thermal gradient along the nipple wall above the bath level. The effect of system outgassing on the adsorption measurements was shown to be negligible. The isotherm data at each temperature were described empirically using the Dubinin-Radushkevich (DR) equation. Complete correlation by the (DR) equation of the temperature dependence of adsorption was not achieved for any of the adsorbates. Mean energies of adsorption calculated from the slopes of the DR plots were 1290, 1545, 1490, and 1903 cal∕mole for Ar, Kr, CH4, and N2, respectively. This is the same order as has been reported for these gases on Pyrex; however, the interaction is about 10% higher on stainless than on Pyrex for each gas. Isosteric heats of adsorption calculated from the DR equation were 4.9, 6.4, 5.9, and 6.2 kcal∕mole for Ar, Kr, CH4, and N2, respectively at θ=0.002.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Contamination in Films Sputtered From Hot-Pressed Targets

J. L. Vossen

J. Vac. Sci. Technol. 8, 751 (1971); http://dx.doi.org/10.1116/1.1315388 (2 pages) | Cited 5 times

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Abstract Unavailable
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Cd Deposition by sputtering

Design and Construction of Small Conductances (10−3–10−6 Torr⋅liter∕sec) for Ultrahigh-Vacuum Applications

Dallas E. Weaver

J. Vac. Sci. Technol. 8, 752 (1971); http://dx.doi.org/10.1116/1.1315389 (2 pages) | Cited 1 time

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Abstract Unavailable
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07.30.Kf Vacuum chambers, auxiliary apparatus, and materials

Argon Cracking Pattern Using a Monopole Mass Spectrometer

V. A. Wells and M. J. Barry

J. Vac. Sci. Technol. 8, 754 (1971); http://dx.doi.org/10.1116/1.1315390 (2 pages)

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Abstract Unavailable
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07.75.+h Mass spectrometers

The Rate of Sublimation of Cleaved Sodium Chloride

E. G. Clarke and A. W. Czanderna

J. Vac. Sci. Technol. 8, 755 (1971); http://dx.doi.org/10.1116/1.1315391 (2 pages)

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Abstract Unavailable
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64.70.Hz Solid-vapor transitions

Erratum: The Flow of Highly Rarefied Gases through Tubes of Arbitrary Length

P. Clausing

J. Vac. Sci. Technol. 8, 756 (1971); http://dx.doi.org/10.1116/1.1315392 (1 page)

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Abstract Unavailable
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47.45.-n Rarefied gas dynamics
47.60.-i Flow phenomena in quasi-one-dimensional systems
99.10.Cd Errata

Simplified All-Glass Device to Open or to Isolate Part of a Vacuum System Repeatedly

Victor R. Deitz

J. Vac. Sci. Technol. 8, 757 (1971); http://dx.doi.org/10.1116/1.1315393 (2 pages)

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Abstract Unavailable
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07.30.Kf Vacuum chambers, auxiliary apparatus, and materials

A Directly Heatable Hydrogen and Oxygen Diffusion Leak

L. C. Burton

J. Vac. Sci. Technol. 8, 758 (1971); http://dx.doi.org/10.1116/1.1315394 (1 page)

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Abstract Unavailable
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07.30.Kf Vacuum chambers, auxiliary apparatus, and materials

Pressures and Consumable-Electrode Arcs

F. W. Wood and E. D. Calvert

J. Vac. Sci. Technol. 8, VM5 (1971); http://dx.doi.org/10.1116/1.1315408 (8 pages)

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An investigation of arc zone pressures during CEVAR (consumable-electrode vacuum-arc remelting) experiments has shown that pressure differences and gradients within furnaces are functions of pressure itself, electrode composition, and the degree of arc-zone confinement. There is evidence also that some previously puzzling contrasts in arc-furnace behavior may be explainable on the basis that two pressure dependent forms of electrical discharge operate with distinct potentials. The lower voltage form tends to become unstable at pressures <0.5 Torr and behaves best at pressures >1 Torr. The higher voltage form seems to be most stable at pressures <0.1 Torr. For continuous operation and maximum versatility, a CEVAR furnace should be able to accommodate both discharge forms by providing for variability of vacuum conditions.
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81.20.-n Methods of materials synthesis and materials processing

Development Related to Rotatrode Melting as Applied to Production Practice

E. von Tiesenhausen and M. Schlienger

J. Vac. Sci. Technol. 8, VM13 (1971); http://dx.doi.org/10.1116/1.1315395 (1 page)

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Two separate aspects of nonconsumable melting of titanium alloys were discussed. The first one dealt mainly with the general characteristics and type of equipment suitable for this type of melting while the second part dealt with actual production experiences on the nonconsumbale furnace using the rotatrode electrode. The major nonconsumable melting systems which are presently in use for reactive metals were mentioned. Emphasis was placed on the actual design criteria used in the developmeut of a nonconsumable furnace with particular emphasis being placed on the three different methods of melting and∕or withdrawing and pouring. Particular emphasis was given to the design and safety interlocks embodied in the various control systems such as the electrode and crucible controls. A short discussion of the viewing and feeding systems was made. Basic variables affecting the nonconsumable arc were discussed. Data taken on the factors affecting arc length, i.e., pressure, voltage, and amperage were presented but no theoretical explanations of the curves were given. While considerable progress has been made in nonconsumable melting technology, a large amount of research and development work still needs to be done.
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07.20.Hy Furnaces; heaters

Scrap Recovery and Casting with a Nonconsumable Electrode

Albert R. Vaia, Ronald R. Akers, and Sam Damon

J. Vac. Sci. Technol. 8, VM13 (1971); http://dx.doi.org/10.1116/1.1315396 (6 pages)

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This report discusses results from melting with water-cooled nonconsumable electrodes since their introduction to the industry at the 1969 Vacuum Metallurgy Conference in Pittsburgh. In production these electrodes have proven to be attractive for the first melting of titanium sponge and scrap directly into remelt electrodes thereby avoiding the electrode fabrication step previously required. They have also been applied to reclamation of small superalloy scrap directly into forgeable ingot avoiding the two-step practices of air induction melting followed by consumable melting and are currently being used to replace the graphite electrode melting and casting of uranium carbide fuel rods. Experiments reported in this paper were conducted to determine the application of the nonconsumable melting technique to some of the many problems in scrap recovery and the casting industry. For example, we have investigated isolation of high density inclusions from titanium scrap, elimination of low density inclusions, effect of superheating on metal fluidity in casting, and the operation of nonconsumable electrodes at low pressure.
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89.20.Bb Industrial and technological research and development
81.20.-n Methods of materials synthesis and materials processing

Analysis of Operational Data of Vacuum Arc and Electroslag Remelting Plant

Hans J. Mueller-Aue

J. Vac. Sci. Technol. 8, VM19 (1971); http://dx.doi.org/10.1116/1.1315397 (5 pages)

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A production plant containing three vacuum arc remelting (VAR) furnaces and one electroslag remelting (ESR) furnace is described. Production of about ten million pounds of a variety of material grades is analyzed by breakdown of the production program by steel grades and ingot size in order to evaluate the economies of the VAR and ESR processes. A realistic annual remelting capacity of the three VAR furnaces is about 11.5 million pounds for a mixed ingot production program with specific requirements of material quality and processing technology, taking into account the factors influencing the possible annual production. A graph illustrating the scattered values of melt rate and power consumption for steel remelted under varying conditions shows that the complexity of the ESR process can lead to very different statements when comparing the VAR and ESR processes. A correct comparison of the advantages and disadvantages of the two remelting processes and an understanding of the economic factors of each process requires a knowledge of the base on which the figures for comparison are determined.
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89.20.Bb Industrial and technological research and development
81.20.-n Methods of materials synthesis and materials processing

Selected Properties of Beryllium-Base Alloys Consolidated by Vacuum-Arc Melting

C. E. Armantrout and C. O. Sims

J. Vac. Sci. Technol. 8, VM23 (1971); http://dx.doi.org/10.1116/1.1315398 (6 pages)

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A preliminary survey of beryllium-base alloys was conducted by melting and testing small button-shaped ingots. Hardness and impact resistance were compared with those of pure beryllium. Structures were examined by microprobe analysis and conventional metallographic techniques. Larger homogeneous ingots of alloys showing promise were then consolidated by consumable electrode arc melting of pressed electrodes of beryllium and the intermetallic compound NiAl. The ingots were formed into rods of 1.7-cm (⅝-in.) diameter at reductions of 9-1 by impact extrusion. Evaluation of the rods was by tensile tests, hardness measurements, and microprobe analysis. Tensile properties at room temperature ranged from about 51 000 to 55 000 psi; tensile modulus was 30−50×106 psi; elongation was about 1% at room temperature and 2–9% at 600 °C.
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81.05.Bx Metals, semimetals, and alloys
81.20.-n Methods of materials synthesis and materials processing

A Technique for Evaluating Titanium Alloys by Melting, Processing, and Testing Miniature Ingots

A. G. S. Morton and R. B. Pond

J. Vac. Sci. Technol. 8, VM29 (1971); http://dx.doi.org/10.1116/1.1315399 (4 pages)

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A technique of melting, processing, and testing small (80 g) rods of titanium alloys has been developed. The technique is designed for screening large numbers of alloy formulations to determine those with enough potential for further evaluation. The hearth plate of an arc button-melting furnace was modified to produce rod ingots which are forged to a shape suitable for testing. Strength and toughness measurements are used to compare a series of alloys relatively, and with respect to their bulk properties. It is recognized that a number of factors, such as cooling rates and amount of forging, prevent duplication of production material properties. Nevertheless, the apparent alloying and microstructural effects and the degree of correlation with plate properties are discussed.
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81.20.-n Methods of materials synthesis and materials processing
81.05.Bx Metals, semimetals, and alloys

Hollow-Cathode Discharge Melting of Ti–6Al–4V and Nb–56Ti–3.3Zr Alloys

Hiromichi Takei and Yuji Ishigami

J. Vac. Sci. Technol. 8, VM33 (1971); http://dx.doi.org/10.1116/1.1315400 (5 pages) | Cited 1 time

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Sound ingots of titanium and Ti–6Al–4V alloy, 110-mm diam×400 mm long, were cast in a 60-kW HHCD furnace. Oxygen and hydrogen levels were reduced considerably. Triple melting and casting of Nb–56Ti–3.3Zr alloy in an 80-kW HHCD furnace produced a satisfactory superconducting material on which test data is reported. A description of the furnace and the operating procedure is outlined.
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81.20.-n Methods of materials synthesis and materials processing
81.05.Bx Metals, semimetals, and alloys

Titanium Casting with Sand Foundry Techniques

Warren Lee

J. Vac. Sci. Technol. 8, VM38 (1971); http://dx.doi.org/10.1116/1.1315401 (1 page)

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The ability to produce a east titanium configuration has a history of approximately 10 years. It is presently being done in the United States by six companies. Casting of titanium is no simple task when one considers the thousands of foundries in existence producing cast parts from other metals. The difficulties are that titanium must be handled more carefully because molten titanium is very reactive to liquids, gases, and solids. At present, consumable vacuum arc melting offers the only suitable commercial method of producing titanium castings. The rapid contamination of titanium at elevated temperature by oxygen and nitrogen and the severe damage to ductility by small percentages of such contaminants requires that melting of titanium be done in the absence of air. Because liquid titanium is an extremely effective solvent, problems of containing the molten metal within a crucible during the melting operation are encountered. A water-cooled copper crucible is used to extract heat so rapidly from the liquid metal that it solidifies before its solvent reaction can take effect. This provides a thin film of solid titanium between the molten titanium and the copper crucible. This is referred to as skull melting. The liquidus to solidus range of titanium is quite narrow and problems of fluidity exist. When enough molten titanium is accumulated in the crucible, the power is cut, the electrode is rapidly withdrawn, and the pot is tilted, all within a few seconds or the pool will solidify. A centrifuge is used within the furnace vacuum chamber during the pouring of the melt. The high g forces during the casting operation help overcome the lack of fluidity. The centrifuge action assists in filling mold cavities with metal densities vastly superior to those from conventional sand foundry static casting. Conventional materials such as sand, shell, or ceramic molds are unsatisfactory for titanium since titanium above or near its melting point will violently react with these materials. A water soluble, expendable graphite mold system is a relatively new development in titanium casting and configurations with close tolerances and excellent surface finish are obtainable. New information related to the production of titanium castings with the latest applied technology was presented.
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81.10.Fq Growth from melts; zone melting and refining
81.05.Bx Metals, semimetals, and alloys

Integrally Cast Airfoil Components for Small Gas Turbine Engines

J. H. Boyle and J. E. Ingalls

J. Vac. Sci. Technol. 8, VM39 (1971); http://dx.doi.org/10.1116/1.1315402 (1 page)

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In the past two decades, remarkable progress has been made in investment casting of airfoil components for gas turbine engines. Cast turbine blades, operating at high stresses and high temperatures, have been widely accepted. Improved production techniques, notably vacuum melting and casting, have stimulated development of greatly improved nickel and cobalt based superalloys. Although individual turbine blades and vanes have been produced in large quantities since 1950, a more recent development is high-volume production of integrally cast turbine wheels and nozzles for small gas turbine engines. This paper is a review of the state of the art in integrally cast airfoil components. The Monoshell process, as applied to integral castings is reviewed and representative illustrations of a wide range of engine castings are presented.
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81.10.Fq Growth from melts; zone melting and refining

Vacuum Casting of Cored Nickel-Alloy Precision Castings

R. J. Quigg

J. Vac. Sci. Technol. 8, VM39 (1971); http://dx.doi.org/10.1116/1.1315403 (1 page)

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Cast-in cooling passages are required to enable superalloy airfoils to stand up at the present day turbine inlet temperatures. These cooling passages are obtained by casting around ceramic cores. These cores engender problems in handling, core distortion, core removal, and wall thickness measurements. In this paper, each of these problems was discussed.
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81.10.Fq Growth from melts; zone melting and refining
81.05.Bx Metals, semimetals, and alloys

Effect of Reduced Pressure Induction Melting on Short Transverse Properties of 7075 Aluminum

Shingo Inouye and Robert A. Sweeney

J. Vac. Sci. Technol. 8, VM40 (1971); http://dx.doi.org/10.1116/1.1315404 (1 page)

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Vacuum degassing techniques have been successfully applied to aluminum alloys for the production of sound, high strength, shaped castings. However, the use of a low-pressure environment during the melting process has not been utilized to the authors' knowledge. This experimental study has been an attempt to combine the desirable features of induction melting, such as uniform mixing and good temperature control of the melt, with an environment of low pressure for degassing of the melt and restricting the supply of reactive gases. The study has been limited to a single high strength wrought alloy: 7075-T6 aluminum. The short transverse ductility of this material is a sensitive indicator of deficiencies in materials and processing. Therefore, emphasis has been placed on the material properties in this direction as a means of evaluating melting variables. An attempt was made to correlate melt variables, such as starting material purity, gaseous environment and oxide removal methods, with tensile properties, stress corrosion properties and endurance limit in the short transverse direction of forged material in the solution treated and aged (T6) condition. Preliminary data was presented.
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81.10.Fq Growth from melts; zone melting and refining
81.05.Bx Metals, semimetals, and alloys

The Reactivity of Vanadium and Some Vanadium Alloys with Low-Pressure Oxygen and Nitrogen

R. C. Svedberg

J. Vac. Sci. Technol. 8, VM41 (1971); http://dx.doi.org/10.1116/1.1315405 (7 pages)

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The reactivity of pure vanadium (<350 ppm total impurity content) and the alloys vanadium–10.5-wt% chromium, vanadium–9.5-wt% molybdenum, and VANSTAR-7 (V–9 wt% Cr–3 wt% Fe–l.3 wt% Zr–0.05-wt%) with oxygen and nitrogen at low partial pressures in the temperature range of 600–800 °C was determined utilizing a hot-wall ultrahigh vacuum microbalance system. The rate of reactivity was determined from continuous weight-gain measurements as a function of both temperature and pressure, for oxygen partial pressures of 10−5 to 10−7 Torr and nitrogen partial pressures of 10−4 to 10−6 Torr. Linear kinetics were observed, indicative of a process controlled by gas transport to the metal surface. The sticking probability for oxygen of 0.185±0.040 was found to be independent of temperature, pressure, and alloying additions. The rate of reaction with nitrogen was a function of alloying additions, with VANSTAR-7 and V-10.5Cr exhibiting the lowest reactivity. The sticking probabilities were compared with those reported in the literature. These results indicate that the sticking probabilities of low-pressure gases on refractory metals are not well defined and seem to be a function of the particular experimental apparatus utilized.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
81.05.Bx Metals, semimetals, and alloys

Low-Pressure Oxidation of Cb–1Zr Alloy

T. F. Lyon

J. Vac. Sci. Technol. 8, VM48 (1971); http://dx.doi.org/10.1116/1.1315406 (11 pages)

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Resistively heated strip specimens of Cb-1Zr alloy were exposed at 927 °C in a vacuum chamber at various levels of total pressure in the 10−6-Torr range and oxygen partial pressures in the 10−7-Torr range. Pressure levels were maintained by controlled in-leakage of air. Oxygen reacts rapidly with Cb–1Zr alloy under these conditions and final oxygen content of the specimens was between 4000 and 9000 ppm for exposure times between 200 and 500 h. Oxygen reaction rates (sticking probabilities) were calculated both from the total oxygen pickup and from the vacuum chamber gas analyses. Good agreement was obtained between the two methods. Oxygen sticking probabilities were found to depend on whether or not the specimens were annealed immediately before the test exposure. These results indicate that a normally undetectable oxide film exists on the Cb–1Zr surface as a result of oxidation by ambient air, and causes the sticking probability to be lower than on the clean metal surface. Sticking probabilities ranged from 0.65 on the clean surface to 0.16 on the surface with the oxide film. Mechanical tests of the contaminated material showed that Cb–1Zr alloy is considerably strengthened by addition of oxygen to an oxygen level of about 6000 ppm, while still maintaining reasonably good room temperature ductility. At higher oxygen levels, the ductility decreases markedly with little additional increase in strength. Welded and annealed Cb–1Zr is considerably more sensitive to oxygen contamination. The weld metal is brittle after addition of 4300 ppm oxygen.
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81.65.Mq Oxidation
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
81.05.Bx Metals, semimetals, and alloys

Influence of Vacuum Environment on the Composition, Structure, and Mechanical Behavior of the Tantalum Tungsten Hafnium Alloy T-111

K. D. Sheffler

J. Vac. Sci. Technol. 8, VM58 (1971); http://dx.doi.org/10.1116/1.1315407 (6 pages)

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Various heats of a tantalum base alloy containing 8% tungsten and 2% hafnium together with 30 to 130 ppm oxygen as a residual impurity were creep tested in a vacuum environment of less than 1×10−8 Torr. Analyses of the residual gas composition indicated that the major constituents of the vacuum environment were carbon monoxide, hydrogen, argon, and water. Loads and temperatures were selected to provide approximately 1% creep strain in times ranging between 1000 and 40 000 h. Chemical analysis of the test materials before and after creep testing indicated that the exposure to the 10−8 Torr environment caused a significant decrease in the amount of oxygen present in the tantalum alloy. This decrease was accompanied by the disappearance of a grain boundary network of hafnium oxide inclusions which was shown by electron microprobe studies to be present in the material prior to testing. This loss of oxygen during testing had a pronounced influence on creep behavior of the T-111 alloy in the 1600–2200 °F temperature range where an oxygen-associated dynamic strain aging effect has been noted. The strain aging behavior appeared to cause an anomalously low creep rate in the early stages of T-111 creep testing; for example, creep rates below 10−8∕h were measured at 1600 °F and 35 ksi. This period of very slow creep was followed by a transition to a much higher creep rate and this transition was thought to occur as a result of the loss of the oxygen from the test material. Analysis of the creep rates measured after the rate transition provided an activation energy value which was the same order as the self-diffusion coefficient for pure tantalum, indicating after the oxygen was lost that creep proceeded by a conventional diffusion controlled process.
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81.05.Bx Metals, semimetals, and alloys
81.70.Bt Mechanical testing, impact tests, static and dynamic loads

Environmental Aspects of Reactive Metal Production

S. A. Worcester and W. A. Aschoff

J. Vac. Sci. Technol. 8, VM64 (1971); http://dx.doi.org/10.1116/1.1315409 (1 page)

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If vacuum metallurgy were the segment of the production of reactive metals with which one needed to be concerned, environmental aspects would be relatively simple to control. Air pollution could be handled by proper use of vapor and mist traps on mechanical pump exhausts and in the vicinity of oil reclaimers. Prevention of water pollution might prove to be more of a problem because of the difficulties in disposing of both mechanical pump and diffusion pump oils. An integrated plant for producing such a metal as zirconium uses relatively large quantities of chemicals which may be detrimental to the environment, if not carefully controlled. Chlorine, hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, ammonia, ammonium thiocyanate, and methyl isobutyl ketone are among those difficult to handle materials encountered in such an operation. Not only is disposal of waste products a potential evnironmental problem, containment of the reagents themselves present some unusual challenges. In many cases, a bootstrap approach is used wherein a reactive metal such as zirconium is found to possess the necessary corrosion resistant and noncontaminating properties highly desirable in equipment used for handling reagents or by-products encountered in its production.
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89.20.Bb Industrial and technological research and development
81.20.-n Methods of materials synthesis and materials processing

Sulfur—Its Effects, Removal, or Modification in Vacuum Melting

Richard S. Cremisio, Joseph G. Cannon, and C. Frank Elliott

J. Vac. Sci. Technol. 8, VM64 (1971); http://dx.doi.org/10.1116/1.1315410 (1 page)

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Sulfur has long been recognized as one of several elements causing considerable property, difficulty in vacuum melting. Once introduced, usually via raw materials, traditional vacuum melting techniques must be modified to reduce sulfur to acceptable levels. Individual effects of sulfur on certain nickel, cobalt, and iron base alloys were discussed. Techniques for the removal of sulfur during vacuum melting were discussed including some thoughts on the kinetics of desulfurization. Among the sulfur removal techniques indicated are the following: Slag Base Metal Reactions Gaseous Purge Techniques Rare Earth Metal or Alloy Innoculation.
The paper gives some new data with regard to the desulfurization of nickel base superalloys (notably Inco 901) by addition of elemental cerium in vacuum induction melting. Desulfurization levels to 0.001 wt% were achieved without any loss in property response or microstructural degradation.
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81.20.-n Methods of materials synthesis and materials processing

Oh! Where Have the Mountains of Titanium Scrap Gone?

Jerry J. Gray

J. Vac. Sci. Technol. 8, VM65 (1971); http://dx.doi.org/10.1116/1.1315411 (7 pages)

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Results of a secondary titanium market survey indicated that an oversupply of titanium scrap does not exist. The mountains of scrap that existed during the late 1950’s and early 1960’s were consumed down to mole hills by the mid to late 1960’s. During the past two and one-half years, even the mole hills’ roots were consumed. The titanium scrap situation is illustrated by a 10-year statistical model (see Table I). The model in the form of a table contains sponge, ingot, and scrap production and consumption statistics. Three assumptions were used, two concerned with fabrication productivity and the third with nonrecoverable scrap losses. Over the total 10-year period, scrap consumption was larger than scrap supply by 7.6%. For the first six years, 18% more scrap was consumed than was generated. For the last four years, scrap supply and demand were in balance, almost within 100 tons. Currently (1969–1970), scrap is in short supply. For the future, table data trends indicate that the short supply will continue. A major effect of the tight supply will be upward pressure on the price of ingot. Scrap is migrating to the steel (including direct alloying and deoxidizing, ferrotitanium production, and exports) and aluminum industries, instead of returning for recycling, because of lower scrap processing costs and technological needs for titanium metal which cannot be met with sponge.
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89.20.Bb Industrial and technological research and development

Miniseptor—A Modular Approach to Susceptor Design

Henry F. Raufer

J. Vac. Sci. Technol. 8, VM72 (1971); http://dx.doi.org/10.1116/1.1315412 (1 page)

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MINISEPTOR is a susceptor for vacuum hear-treat and melting applications which is made up of a number of multisided polygons, (almost circular rings) primarily of graphite, stacked concentric with the axis of an induction coil. Its modular construction makes feasible hot zones, as large as 11 ft in diameter by 17½ ft high, for operating temperatures to 2750 °C (5000 °F). The reduced mass of the susceptor greatly reduces the stored energy in the susceptor resulting in brisk, temperature cycling. In addition, initial costs and operating costs are lower than for conventional systems. The modular construction of the susceptor and its thermal insulation allows replacement in sections as required, without complete removal, which simplifies maintenance and lowers the required minimum stock of spare parts. Variable configuration of the bars, pins, fit, and grade of the graphite used affect the overall resistance of each ring, the number and configuration of rings determining the power delivered to the susceptor at any given voltage and frequency. The multiplicity of independent concentric “rings” permits altering the spacing between “rings” so that it is possible to control the temperature gradient by distribution of the power along the length of the hot zone. Performance characteristics observed on a hot zone 35 in. in diameter and 51 in. tall are discussed. Uniformity of the temperature gradient across the hot zone and holding temperatures observed on this scale model of the large hot zone described above are reviewed.
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07.20.Ka High-temperature instrumentation; pyrometers

Model for Calculating the Deposit Temperature in High-Rate Physical-Vapor-Deposition Process

Raymond Chow and R. F. Bunshah

J. Vac. Sci. Technol. 8, VM73 (1971); http://dx.doi.org/10.1116/1.1315413 (6 pages)

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81.15.Aa Theory and models of film growth

Investigation of Factors Affecting the Composition of an Alloy Coating Deposited by Sputtering

W. R. Stowell, D. L. Chambers, and D. C. Carmichael

J. Vac. Sci. Technol. 8, VM79 (1971); http://dx.doi.org/10.1116/1.1315414 (1 page)

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Sputtering of relatively thick deposits of alloys for use as protective coatings has shown that the composition of the target is usually not exactly reproduced in the deposit. The elemental values of sputtering rates also do not apply directly to sputtering from alloys, although they are useful in examining the change in alloy composition of the deposit as compared to the original target. To investigate some of the basic relationships involved, a study is being conducted on the sputtering of the system copper–silver. This is a simple eutectic system and thermodynamic data are available. Results of experiments on sputtering of this alloy was presented and underlying relationships were discussed. Substrate biasing has been found to significantly affect the deposited composition of sputtered alloys. The effect of an increasing substrate bias on the composition of sputter-deposited copper–silver alloy was examined in this investigation and the result related to the basic alloy properties. The interaction of deposition variables such as sputtering rate and substrate temperature was also discussed. Copper off-sputters from a forming film more rapidly than does silver. This result is unexpected because the sputtering yield for silver is higher than for copper.
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81.05.Bx Metals, semimetals, and alloys
81.15.Cd Deposition by sputtering

Effect of Deposition Temperature on Condensed Phases in Sputtered Ni–Cr Thick Films

C. Panzera, R. C. Krutenat, and M. J. Donachie

J. Vac. Sci. Technol. 8, VM80 (1971); http://dx.doi.org/10.1116/1.1315415 (6 pages) | Cited 2 times

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A modified triode sputtering technique was used to deposit nickel-chromium alloys on pure nickel substrates maintained at temperatures varying from 550 to 1050 °C by controlled, low energy electron bombardment heating. The coatings (110–200 μ thick), deposited at rates between 960 and 1400 Å∕min, were evaluated utilizing metallographic, chemical analysis, electron microprobe, x-ray diffraction, and electron diffraction techniques. A new phase, designated ϵ, was found when Ni-22 at.% Cr was deposited at temperatures above 750 °C. The volume fraction of the new phase increased from 10% at 750 °C to 13% at 1050 °C. Heat treatment for 200 h at 1050 °C showed no change in volume fraction of ϵ previously deposited at that temperature, indicating that ϵ is the equilibrium phase. The ϵ phase containing 87 at.% chromium had a tetragonal structure with a c∕a=0.55, and a columnar-plate habit and grew perpendicular to the interface. The alloy target containing 12 at.% chromium condensed as ϵ+γ between 750 ° and 950 °C but only γ at 1050 °C. A tentative phase diagram section has been proposed showing the relationship between ϵ and γ, and α phases.
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81.05.Bx Metals, semimetals, and alloys
81.15.Cd Deposition by sputtering

Temperature and Thickness Distribution on the Substrate during High-Rate Physical Vapor Deposition of Materials

Rao Nimmagadda and R. F. Bunshah

J. Vac. Sci. Technol. 8, VM85 (1971); http://dx.doi.org/10.1116/1.1315416 (10 pages) | Cited 1 time

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In high-rate physical-vapor-deposition processes, the thickness of the deposit and the temperature vary along the substrate. The deposition temperature has a strong effect on grain size and density of the deposit. The deposition rate, thickness variation, and temperature variation depend on the 15 experimental variables, viz., evaporation temperature, source to substrate distance, source diameter, etc. This paper illustrates a method of calculating the temperature and thickness distribution of the deposit. The deposition of yttrium and yttria are used as examples to illustrate the actual range of experimental conditions to be explored. An estimate of probable errors in calculated temperatures due to errors in the emittance data used is made. Radiation from the evaporating source, condensation of vapors, and the reaction of the elements are the sources of heat input to the substrate and the relative contributions of these are calculated for various experimental conditions.
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81.15.Aa Theory and models of film growth

High-Rate Physical Vapor Deposition of Hafnium Foil—A Feasibility Study

R. F. Bunshah and R. T. Webster

J. Vac. Sci. Technol. 8, VM95 (1971); http://dx.doi.org/10.1116/1.1315417 (4 pages)

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The high-rate physical-vapor-deposition process has been used to produce high-purity ductile hafnium foil. The ductility of the foils in the 0.001–0.002-in.-thickness range is excellent. The thinner foils (<0.001 in. thick) are considerably less ductile. There appears to be an inverse correlation between the ductility of the foil and the number of pinholes. Elimination of these should improve the ductility of the thinner foils.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.60.Bs Mechanical and acoustical properties

Investigation of Hot-Filament and Hollow-Cathode Electron-Beam Techniques for Ion Plating

C. T. Wan, D. L. Chambers, and D. C. Carmichael

J. Vac. Sci. Technol. 8, VM99 (1971); http://dx.doi.org/10.1116/1.1315418 (6 pages) | Cited 1 time

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The ion plating process has been generally limited to low-melting materials in past coating applications. In this study, several electron-beam melting techniques have been investigated which provide methods for melting various high-melting-point materials within a glow discharge atmosphere. The magnetically focused hot-filament and the cold-hollow-cathode electron sources have been experimentally studied to evaluate their operational and evaporation-deposition characteristics for the ion plating process. The hollow-cathode electron source emits an intense electron beam and is capable of delivering very high beam power. The gun is made of high melting-point sheets or screens formed into a hollow cylinder or sphere having an aperture to allow the emittance of electrons. It operates in an inert-gas, glow discharge environment such as that of ion plating. Gas pressure is a key processing variable in controlling the mode of operation; the hot-cathode mode operates at high pressures with excellent stability and the cold-cathode mode operates at low pressure and is sensitive to gas pressure variation. The operational characteristics of conventional hot-filament electron-beam guns are also described for this type of application. Evaporation-deposition parameters and techniques for each type of electron source have been determined using various materials. Type 304 stainless steel, titanium, iron chromium-aluminum-yttrium, and other alloys and metals have been successfully deposited and the coatings evaluated. The uniformity and adhesion of the coatings were experimentally investigated and are reported for various source and process conditions.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
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