Ion beam nitriding of titanium and titanium alloy

Titanium and Ti8A/1Mo1V alloy have been nitrided with an ion beam source of nitrogen or agon and nitrogen, at a total pressure of 2?10×10^?4 torr. The treated surface has been characterized by surface profilometry, X-ray diffractometry, Auger Electron Spectroscopy (AES), and microhardness measurements. It was found that tetragonal Ti₂N phase forms in pure titanium and Ti8A/2Mo1V alloy with traces of AIN in the alloy. Two opposite processes were found to compete during the ion beam nitriding: (a) formation of nitrides in the surface layers; (b) sputtering of the nitrided layers by the ion beam. The highest surface hardness, of about 500 kg mm^?2 in titanium and 800 kg mm^?2 in Ti8A/1Mo1V, was obtained by nitriding with an ion beam of pure nitrogen at 4.2×10^?4 torr, at beam voltage of 1000 V.     

Sorption kinetics of oxygen at very low pressures by zirconium

The sorption rate of oxygen by zirconium at very low pressures of 4×10^?6 to 4×10^?4 torr has been investigated in the temperature range 500–850°C using a microbalance. The rate law of sorption was separable into two types, i.e., the linear rate law in the initial period and the parabolic rate law in the latter period. In the initial linear sorption, the rate was exactly proportional to the oxygen pressure at each temperature.The data of sorption kinetics of zirconium were rearranged from the viewpoint of vacuum technology, i.e., sticking probability and pumping speed in bulk gettering.The transition in the rate law of sorption is discussed on the bases of Wagner's model which involves simultaneous scale formation and oxygen dissolution into the metal bulk.     

Precise temperature control by a manostat utilizing a sheet of a thin film material

A new type of manostat has been developed, in which a thin-film material is utilized. It is possible to control the liquid He vapour pressure within 0.1 Torr (1.3 × 10 Nm^?2) in the range between 1 atm (1.01 × 10⁵Nm^?2) and 4 Torr (5.3 × 10²Nm^?2) by use of a thin polyethylene film sheet.     

The design and operation of a new extractor gauge for UHV pressure measurements

The design of a new extractor gauge is described for ultra high vacuum pressure measurements. which employs a separate extractor electrode external to the grid. The advantages to be gained by the use of this system, the importance of providing an adequate ion extraction field and also of preventing the flow of electrons into the collector region, are discussed. A method is described of reducing the effect on the residual current of X-rays reflected onto the collector. This allows a residual current of 10^?14 A, at 1 mA electron current, to be achieved. For a gauge sensitivity of 10 torr^?1 this is equivalent to a residual pressure of 1 × 10^?12 torr. The addition of a modulator has been found to give a high modulation factor of 0.95 which should enable the low pressure limit to be extended to below 10^?14 torr.     

Bombardon: an apparatus for investigating the influence of 5–20 keV ions on metal targets

An apparatus for ion bombardment in the energy range of 5–20 keV is described. The ion beam, produced by a duoplasmatron ion source, is purified by a magnetic sector field and directed into a target chamber 60 cm in diameter. The chamber is evacuated by sputter ion and titanium sublimation pumps with a total pumping speed of 20000 ls^?1 for H₂. The energy and angular distributions of particles backscattered from metal targets can be measured with an electrostatic spherical condenser which can be pivoted around the target. The whole apparatus is bakeable up to 250°C. With a 100 μA proton beam a pressure of 10^?9 torr is maintained in the target chamber. The black off pressure is a few 10^?11 torr.     

The effect of high magnetic fields on the vapour pressures of nitrogen,oxygen and argon

Equations are derived for predicting the change in the vapour pressure curves of oxygen, nitrogen and argon in the presence of high magnetic fields. The Gibbs energies of the vapour and liquid phases are equated, thus producing a ‘magnetic Clausius Clapeyron’ equation. The theoretical results are compared with experimental data measured at fields up to 9.5 × 10⁶ Am^?1, using a specially designed cryostat and sample holder.It was found that the effects on the vapour pressure curves of nitrogen and argon were insignificant at any field strength. For oxygen, the effect was small and only accurately measureable at very high fields. The agreement between the theoretical and practical results was good.An effect on the vapour-liquid equilibrium curve for nitrogen-oxygen mixtures predicted by previous authors,² by virtue of an effect on the vapour pressures of the pure components, is unlikely to occur.     

8. A specimen-exchange device for an ultra-high vacuum atom-probe field-ion microscope

A specimen-exchange device is described for an ultra-high vacuum field-ion microscope (FIM). This device completely eliminates the long pump-down period that is required if the FIM chamber is brought back to atmospheric pressure. The pressure in an air-lock is reduced to 10^?6 torr before the exchange takes place and the pressure in the FIM chamber remains below 10^?7 torr during the exchange and it drops to less than 3 × 10^?9 torr within 15 min after the exchange.     

Comparison of two pumping speed measuring methods of oil diffusion pumps

This paper presents a comparative study of two pumping speed measurement methods recommended for oil diffusion pumps. The methods used are the test dome method and the conductance tube method with an auxiliary pumping system which is used at very low pressures when the throughput is below 10^?5 Nm s^?1 (～ 0.1 μl s^?1). It is found that, in order to obtain the comparative results in the overlapping pressure region on the speed measurement of oil diffusion pumps by these two methods, the conductance tube in the conductance tube method should be located at a height 1.2 D from the pump mouth when the position of the inlet gauge is at a distance D/2 from the pump flange, i.e. at the same position as recommended in the dome method to obtain the intrinsic speed of the pump.     

Mass spectrometric determination of oxygen at partial pressures of less than 1.5 μPa (10−8 torr)

During an investigation of chemisorption and photodesorption reactions between oxygen and thin films of zinc oxide, the need arose for the determination of oxygen partial pressures in the range 1 μPa to 100 pPa (10^?8 to 10^?12 torr), in a static system, using a residual gas analyzer. Within this range the pumping actions for various components of the vacuum system were significant and this paper describes these actions and the techniques developed to lower the limit of detection of oxygen by mass spectrometric analysis to about 700 pPa .l (5 × 10^?12 torr .l)     

Continuous adsorption refrigerator for producing temperatures below 1 K

This paper describes an evaporation refrigerator in which the pumping of the vapour above liquid He³ or He⁴ was accomplished with two alternately operating adsorption pumps. In this way temperature can be maintained constant with an accuracy to ～0.003 K for a long time; ～ 10 l helium vapour being used. The refrigeration capacity of the apparatus has been determined.The characteristics of the dilution refrigerator (namely, the rate of He³ circulation, the starting and operating temperatures) have been calculated for He³ circulation using the adsorption pumps and pumping line.This system is shown to be successful for producing very low temperatures at an He³ circulation rate of ～ 10^?5?10^?4 mole s^?1.     

Plutonium dioxide catalyzed reaction between H<Subscript>2</Subscript> and O<Subscript>2</Subscript>

The kinetic characteristics of the reaction between H₂ and O₂ were calculated to more adequately simulate the radiolysis of water adsorbed on PuO₂. The rate constants of this reaction were determined via comparison of the calculated results with the published experimental data. It was found that, with the amount of the adsorbed water increasing from 2 × 10^?4 to 5 × 10^?3%, the rate constant of the reaction decreases from 6.0 × 10^?4 to 1.7 × 10^?5 mol^?1 s^?1. At the water content over 5 × 10^?3%, the rate constant is ≤1 × 10^?5 mol^?1 s^?1. A new mathematical model of the radiation-chemical and physicochemical processes occurring in the PuO₂-H₂O system was presented; the amounts of hydrogen and oxygen yielded by α-radiolysis of the adsorbed water were calculated, taking into account the reaction between H₂ and O₂.     

Measurement of the Diffusion Coefficient of Water in RP-3 and RP-5 Jet Fuels Using Digital Holography Interferometry

The diffusion coefficient of water in jet fuel was measured employing double-exposure digital holographic interferometry to clarify the diffusion process and make the aircraft fuel system safe. The experimental method and apparatus are introduced in detail, and the digital image processing program is coded in MATLAB according to the theory of the Fourier transform. At temperatures ranging from 278.15 K to 333.15 K in intervals of 5 K, the diffusion coefficient of water in RP-3 and RP-5 jet fuels ranges from 2.6967?×?10 ^?10 m²·s^?1 to 8.7332?×?10 ^?10 m²·s^?1 and from 2.3517?×?10 ^?10 m²·s^?1 to 8.0099?×?10^?10 m²·s^?1, respectively. The relationship between the measured diffusion coefficient and temperature can be well fitted by the Arrhenius law. The diffusion coefficient of water in RP-3 jet fuel is higher than that of water in RP-5 jet fuel at the same temperature. Furthermore, the viscosities of the two jet fuels were measured and found to be expressible in the form of the Arrhenius equation. The relationship among the diffusion coefficient, viscosity and temperature is analyzed according to the classic prediction model, namely the Stokes–Einstein correlation, and this correlation is further revised via experimental data to obtain a more accurate predication result.     

Study of a liquid helium jet pump for circulating refrigeration systems

A basic diagram of the refrigeration system, in which liquid helium is circulated by means of a jet pump, is described. The equations have been derived to design jet devices which operate with liquid helium.In the experimental setup with a jet pump the flow rate of liquid was 5 to 10 times larger than that of compressed gas in a direct stream of the refrigerator. After pumping the pressure was equal to (0.15–0.40) × 10⁵Nm^?2. A circulating stream of liquid helium at supercritical pressure, due to the heat load corresponding to the refrigerator capacity, was heated to 0.15–0.25 K.The results of our studies permit one to determine circulation loop parameters and main geometric dimensions of the jet pump.     

Investigations on the heat transfer of boiling binary refrigerant mixturesEtudes sur la transmission de chaleur des mélanges de fluides frigorigènes binaires en ébullition

Heat transfer during nucleate pool boiling was experimentally determined for the mixtures R-12/R-113, R-22/R-12, R-13/R-12, R-13/R-22 and R-23/R-13. For purposes of comparison, the respective five pure refrigerants were also investigated. Dependent upon the mixture, the measurements were made at boiling pressures of p = 0.1 to 2 MPa within the temperature region of t = 198 to 333 (?75° + 60°C) and at heat fluxes of Q = 4 × 10³ to 10⁵ W m^?2. A horizontal, electronically heated copper plate with A = 3 cm² was used. The following quantities were measured: pressure; temperature difference between the heating surface and the boiling liquid; composition and temperature in the liquid and vapour phases; and heat flow rate. The mean error of the heat transfer coefficients found was ± 5%.The results clearly show that the heat transfer for an evaporating mixture deteriorates as compared to the pure components. Essential parameters influencing this reduction are pressure, difference between vapour and liquid composition and heat flux. The fundamental relations and characteristic differences between the individual mixtures are illustrated by figures. The heat transfer coefficients measured can be represented within the whole region studied by a modified relation according to Körner.Observation of the process of evaporation has shown that by agitation (increase of convection) the heat transfer in mixtures can be improved. Additional experiments with evaporation during fluid flow in a pipe are presently in progress.     

Forced convection heat transfer to liquid helium I in the nucleate boiling region

Heat transfer and critical heat fluxes to helium boiling in a 2 mm id copper tube (100 mm long) were measured in the pressure range 1.1–1.5 atm and at mass velocities 18–96 kg m^?2s^?1. Corresponding Reynolds numbers are (1.2–6.2) × 10⁴. Experimentally obtained heat transfer coefficients show satisfactory agreement with those calculated according to the Kutateladze equation but with less pronounced pressure dependence. It was found that in the boiling region developed quality did not influence the heat transfer coefficient. An expression was obtained, which describes with ±10% error, the dependence of critical heat flux on mass flow rate in the pressure range 1.1–1.5 atm and mass quality 0.33–0.6.     

Superplastic behaviour of as received superplastic forming grade IN718 superalloy

Abstract

Tensile specimens of superplastic forming grade IN718 superalloy, containing banded microstructure in the as received state, were deformed at high temperatures T to investigate the stress σ versus strain rate ? · behaviour, the nature of the stress versus strain ? curves, ductility, and microstructure upon failure. The log σ–log ? · plot for the ? · range ～5 × 10^-6–3 × 10^-2 s^-1 at T = 1173–1248 K exhibited a strain rate sensitivity index m = 0·62 at low strain rates and m = 0·26 at high strain rates, representing region II and III behaviour, respectively. The activation energies were estimated to be 308 and 353 kJ mol^-1, respectively. All the σ–? curves, obtained at ? · = 1 × 10^-4 s^-1 for the temperature range 1173–1273 K, and at T = 1198 K for the strain rate range 1 × 10^-4–1 × 10^-2 s^-1, exhibited initial flow hardening, followed by flow softening. The microstructures revealed dynamic recrystallisation, grain growth, cavitation, and a variation in the amount of second phase particles. Grain growth and cavitation were found to increase with temperature in region II. Excessive grain growth at 1273 K led to the elimination of region II. Grain growth and cavitation were both found to be less pronounced as the strain rate increased in region III.     

Effects of directional grain structure on impact properties and dislocation substructure of 6061-T6 aluminium alloy

Abstract

The effects of the grain structure direction on the impact properties and dislocation substructure of 6061-T6 aluminium alloy are investigated under room temperature conditions and strain rates of 1×10³, 3×10³ and 5×10³ s^?1 using a split-Hopkinson pressure bar system. The impact tests are performed using specimens machined from rolled 6061-T6 plates in the longitudinal, transverse and through thickness directions respectively. The results show that for all specimens, the flow stress increases with increasing strain rate. Furthermore, for all strain rates, the highest flow stress occurs in the transverse specimen. For strain rates of 1×10³ and 3×10³ s^?1, the flow stress in the through thickness specimen is greater than that in the longitudinal specimen. However, at a strain rate of 5×10³ s^?1, the flow stress in the longitudinal specimen is higher than that in the through thickness specimen due to a greater dislocation multiplication rate. For all three grain structure directions, the strain rate sensitivity increases with increasing strain rate, but decreases with increasing true strain. The highest strain rate sensitivity is observed in the longitudinal specimen at strain rates of 3×10³ to 5×10³ s^?1. The dislocation density increases markedly with increasing strain rate. Moreover, the square root of the dislocation density varies as a linear function of the flow stress in accordance with the Bailey–Hirsch relationship. The strengthening effect produced by the increased dislocation density is particularly evident in the transverse specimen, followed by the longitudinal specimen and the through thickness specimen.     

Heat transfer and hydrodynamics of channelled cryogenic liquids in fields of centrifugal forces

This Paper reports experimental results on the hydrodynamics and heat transfer during a free-convective and forced motion of cryogenic liquids within a channel in the field of centrifugal forces. Investigations were carried out on the hydrodynamics and heat transfer of a two-phase flow of nitrogen and helium in the heated axial part of the ⊓-shaped duct in the 50–300 range of relative accelerations. It was found that during the free-convective motion the volume flow of liquid nitrogen, with heat fluxes varying from 3 × 10³ to 1 × 10⁴Wm⁻², increased more than 30 times. The volume flow is accompanied by large oscillations and increases with growing relative accelerations. The heat transfer coefficients also are shown to grow with the relative acceleration, which is due to an increase in the hydrostatic pressure at the radial inlet of the duct. Experimental results are presented concerning the heat transfer intensity during forced motion of two-phase helium along a heated axial channel of a rotating □-shaped duct at flow rates <- 7.5 × 10⁻⁵kgs⁻¹. At the relative acceleration of ≈ 100 the heat transfer and critical heat flux are observed to increase with the flow rate. At flow rates <- 10⁻⁴ kg s⁻¹the heat transfer to helium is the same as during pool boiling.     

High strain rate superplasticity of ultrafined Ti–10V–2Fe–3Al compact prepared by sintering and isothermal forging

Abstract

High strain rate superplasticity was obtained for powder Ti–10V–2Fe–3Al (Ti-1023) alloy prepared by powder sintering and isothermal forging technology. The selected powder was cold isostatic pressed, sintered and isothermal forged to prepare this powder alloy. Tensile testing was conducted at optimum superplastic temperaure of 1023 K with different initial strain rate, and the elongation to failure, the flow stress and the microstructure were analysed. The experiment results exhibited that the microstructure of this powder alloy is extraordinary uniform and fine, resulted in considerable enhancement of optimum initial strain rate increased from 3·3×10^?4 s^?1 of conventional cast and wrought Ti-1023 alloy to 3·3×10^?3 s^?1 of this powder alloy. The elongation to failure increased first and then decreased with initial strain rate from 3·3×10^?4 to 3·3×10^?2 s^?1. The strain rate sensitivity m is about 0·46 near initial strain rate of 3·3×10^?3 s^?1, larger than conventional cast and wrought Ti-1023 alloy. Microstructure observations showed that dynamic recrystallisation and grain growth were present during superplastic deforming.     

Investigation by techniques of electron stimulated desorption of the merits of grow discharge cleaning of the surfaces of vacuum chambers at the CERN intersecting storage rings

To provide surface cleaning of the CERN intersecting storage rings, in which the pressure is below 10^?10 torr over a 2 km length of mostly elliptical pipe (160 X 52 mm), ion bombardment during a glow discharge has been utilized. The discharge in argon at a pressure of about 3 × 10^?2 torr was carried out intermittently in the course of a 15 h bake-out at 300°C. Subsequent electron scrubbing enabled the electron desorption efficiency of the surface of the ISR vacuum chambers to be reduced by two to three orders of magnitude. Information is given on the apparatus used and the procedure adopted, together with a discussion of the diagnostic technique and a consideration of the action of the discharge cleaning.