Spatial parameters of the electron beam in interaction with a magnetized target

Abstract:

Prestress shot‐blasting is known to improve the fatigue strength of welded joints. With aluminium alloys, specific criteria must be followed. If this is done, surprising results are found, indicating a very promising development.     

Welding of high-alloy Cr-Ni steels with a magnetically impelled arc and auxiliary electrode

Abstract

An accoúnt is given of an MIAF welding installation for tube to sheet welding with end-face flush-weld preparation, and the problems of its introduction into industry.     

Production-scale molecular beam epitaxy for high-frequency applications

Molecular beam epitaxy wafers are now firmly established as a major component in the production of devices for high-frequency applications. As the markets for such devices mature, producers will face increasing pressure to improve quality and increase volume while continuing to lower prices. Frank J. Bruni earned his PH.D. in metallurgy at the University of Oxford in 1970. He is currently vice president of Picogiga. Linh T. Nuyen earned his Ph.D. in physics at the University of Paris in 1970. He is currently chair of Picogiga.     

Electron beam hardening for the regeneration of turbine blades

Abstract

Wear-resistant protective zones, restricted to pre-set areas on the rotor blades of turbines and made from heat-treatable steels alloyed with chrome, can be produced efficiently by electron beam (EB) hardening. The EB plant of type ESA 150-MR is suitable for carrying out hardening processes on small numbers of blades in combination with a component-specific positioning device.

The method and instruments described here were used to make a fairly large number of turbine blades fit for use again by reconstruction after destruction by erosion.     

Using electron beam surfacing for producing hardened layers on the surface of silumin pistons

Summary

This study relates to the influence of microstructure on resistance to the phenomenon of intergranular corrosion in a 24.4Cr7.4Ni duplex stainless steel. The results obtained are discussed as a function of Huey tests and examination by scanning electron microscope. The TTS diagram corresponding to the experimental conditions under which the tests were carried out is also presented.     

Prediction of penetration depths during electron beam welding

Abstract

An analytical penetration model for electron beam welding is presented, based on a combination of the moving line source solution and the solution for a cylindrical cavity moving through a plate of finite thickness. The input parameters are the net beam power, welding speed, keyhole wall temperature, and diameter of the electron beam from which the penetration depth can be calculated for a range of base materials, such as stainless steels, titanium grade 2, and aluminium alloy AA 5052. It is concluded that the penetration model is sufficiently comprehensive and relevant to be used as a predictive tool in ordinary production welding and some possible applications are briefly outlined.     

Inhibitor protection and corrosion monitoring in Benfield installation to purify gas for synthesis

Abstract

The aggressive media in the Benfield processfor preparing gasfor use in synthesis by means of ‘potassium purification’ consist of KHCO₃ + K₂CO₃ solutions having total contents and molar ratios that vary over a very wide range which also contain diethanoloamine. Operating temperatures are typically 70–120°C. Despite the use of inhibitors, intensive corrosion of mild steel walls has been observed in several installations. In laboratory tests performed in simulated Benfield solutions, a relationship has been established between the inhibitor content necessary to suppress active dissolution and pitting corrosion and the total content and molar ratio of the carbonates. These results have been checked and verified in an industrial installation. The corrosion monitoring system applied to critical parts of the equipment allowed the solution composition to be controlled and an inhibitor content appropriate to the composition of the aggressive medium to be maintained. As a result, substantial decreases in corrosion have been achieved, as was confirmed by microscopic examination of disposable electrodes and by the observation of the inner surface of an installation during routine maintenance.     

Suppression of porosity in beam weaving laser welding

Abstract

The present paper describes a beam weaving laser welding technique to suppress argon or nitrogen porosity, which may appear during laser welding of low carbon steel. Bead on plate welding was performed using a 3 kW CO₂ laser. The weaving frequency was varied within 0–30 Hz and the weaving amplitude within 0–2 mm during welding. The experimental results show that under 2.4 kW laser power and 1.0 m min^-1 welding speed, the nitrogen porosity decreases remarkably with increasing frequency, and it can be eliminated for a weaving frequency of 22 Hz with 0.5 mm weaving amplitude. Under 2.4 kW laser power and 1.5 m min^-1 welding speed, beam weaving laser welding can also effectively reduce argon porosity at a weaving frequency of 22 Hz and amplitude of 1.0–1.5 mm.     

Laser beam welding of wrought aluminium alloys

Abstract

Laser beam welding is now a common manufacturing method for a wide range of steel products from automobiles to razor blades. However, the process has only recently been approved for critical applications involving aluminium alloys, notably in the aerospace and automotive industries. The properties of aluminium alloys influence the interaction between the beam and the material to a far greater extent than for steels. The challenge of developing industrial welding procedures has therefore been considerable. The present review describes the effects of CO₂ and Nd–YAG laser beam processing parameters and the properties of the most common wrought aluminium alloys on the characteristics of welded joints. Porosity, solidification cracking, and poor weld bead geometry are shown to be the most frequently encountered imperfections. These can be eliminated through the use of appropriate filler materials, process gases, material preparation, and in some instances, adaptive control systems. Very little work has been reported on the corrosion properties of laser welded aluminium alloys. Experimental processing parameters are presented and compared using an analytical model, which can also be employed for predictive purposes. A number of industrial applications are described. These demonstrate that, for specific alloys, the process is now sufficiently well understood to be approved for high volume production, particularly in the transport industries.     

Coupled effect of heat input and beam oscillation on mechanical properties of alloy 718 electron beam weldments

Abstract

Autogenous full penetration electron beam welds were made on alloy 718 with and without beam oscillation technique. Weldments were subjected to two types of post-weld heat treatments: direct aging (DA) and solution treatment at 980°C followed by aging (STA). When the welds were prepared using different heat inputs in the welding processes with and without beam oscillation, the influence of beam oscillation could not be studied in isolation but the coupled effect of heat input and beam oscillation was studied. Laves particles were finer in size and lower in amount in unoscillated welds compared with those in beam oscillated welds subjected to DA condition. δ phase needles were observed around Laves particles in the welds subjected to STA condition. The amount of Laves particles was less and that of δ phase was more in unoscillated welds compared with those in beam oscillated welds subjected to STA condition. Unoscillated weldments exhibited longer fatigue lives compared with beam oscillated weldments in both DA and STA conditions owing to less amount of Laves in the former. Weldments in STA condition had longer lives compared with those in DA condition. The role of δ phase needles in fatigue life could not be identified.     

Effects of activating fluxes on pulsed laser beam welded AZ31 magnesium alloy

Abstract

Effects of activating fluxes on macromorphologies, microstructures and mechanical properties of low power pulse laser beam welding of AZ31 magnesium alloy joints were investigated by microstructural observations and mechanical properties tests (including the ultimate tensile strength and hardness). The results showed that activating flux (SiO₂) is more effective in improving the laser welded penetrations when the heat input is at a critical value (E?=?53·42 J mm^?1). Five typical fluxes (SiO₂, TiO₂, ZnCl₂, CaCl₂ and CaF₂) all increased the weld penetrations and D/W ratios of the welded joints. The morphologies of grains in the band zones with fluxes are characterised by dendritic crystals. Moreover, the widths of the band zones with oxide and chloride fluxes are wider than that with fluorine flux. The mechanical properties of the welded joints with fluxes were lower than those without flux. The fracture surface of the welded joints with fluxes exhibited a character of a mixed fracture.     

Joining of materials with millimetre-wave beam source

Abstract

An 83 GHz gyrotron-based, millimetre-wave beam system is being used for a range of material processing. One very promising application of this technology is in joining of ceramic and ceramic composite materials and has unique advantages over competitive techniques. The significant advantage is localisation of heating, with the millimetre-wave beam controlled by reflective optics, permitting inexpensive fixturing and instrumentation and minimising thermal damage to components. Another is the possibility of depositing energy specifically in a narrow joint region, through a guided wave effect. A corollary advantage of the process is the possibility of very rapid thermal cycling during joining, minimising thermal degradation of materials being joined.     

Structure and properties of amorphous diamond-like carbon films produced by ion beam assisted plasma deposition

The microstructure and tribological properties of carbon film produced by ion beam assisted plasma deposition in a plasma source ion implantation (PSII) chamber with energies varied from 0 to 30 keV are examined. The process is illustrated schematically, and Raman spectra as well as TEM images and corre-sponding diffraction patterns of carbon films are shown.     

Mechanical properties and strengthening mechanisms in laser beam welds of pure titanium

Abstract

The mechanical properties and strengthening mechanisms in laser beam welds of pure titanium were investigated. Although grain coarsening is evidently observed in the heat affected zone (HAZ) and fusion zone (FZ) compared with the base metal (BM), the tensile and hardness tests indicate that the HAZ and FZ are stronger than the BM under the welding conditions employed in the present work. The strengthening mechanism in the HAZ is ascribed to the substructure strengthening and that in the FZ is attributed to the combination of the substructure strengthening and the solute solution strengthening.     

Influence of tool design on mechanical properties of AZ31 friction stir spot welds

Abstract

The influence of tool design on the energy output, microstructural features and overlap shear strength properties of friction stir spot welds made of AZ31 base material is examined. The mechanical properties of AZ31 friction stir spot welds made using three-flat/threaded tools are superior to those in joints made using a tool with a threaded pin at all tool rotational speed settings. It is proposed that the failure load properties are optimised when the friction stir spot welding operation is carried out in such a manner that it produces a large bonded width, a small v/t ratio (the height of the hook region above the sheet intersection divided by the thickness of the upper sheet) and a hook region, which is curved outwards from the tool axis.     

Technical note Stress corrosion cracking of ammonia receiver tank

Abstract

A 900 t/day capacity installation, used for recycling of ammonia to a urea plant, with two ammonia streams and four receiver tanks, failed after 3 years in service. The vessels were of the cylindrical bullet type, made of SA 516 grade 70 carbon steel. Of the four receiver tanks, only one suffered stress corrosion cracking, caused by incomplete mixing of the 0·2% water required by the process parameters. The vessel was operated at ambient temperature and a pressure of 1·765 x 10⁶ Pa; the design pressure of the vessel was 2·256 × 10⁶ Pa.     

Refining the macromolecular model – achieving the best agreement with the data from X-ray diffraction experiment

ABSTRACT

Refinement of macromolecular X-ray crystal structures involves using complex software with hundreds of different settings. The complexity of underlying concepts and the sheer amount of instructions may make it difficult for less experienced crystallographers to achieve optimal results in their refinements. This tutorial review offers guidelines for choosing the best settings for the reciprocal-space refinement of macromolecular models and provides practical tips for manual model correction. To help aspiring crystallographers navigate the process, some of the most practically important concepts of protein structure refinement are described. Among the topics covered are the use and purpose of R-free, geometrical restraints, restraints on atomic displacement parameters (ADPs), refinement weights, various parametrizations of ADPs (full anisotropic refinement and TLS), and omit maps. We also give practical tips for manual model correction in Coot, modelling of side-chains with poor or missing density, and ligand identification, fitting, and refinement.     

Electron meets nitrogen: combination of electron beam hardening and nitriding

Abstract

Combined heat treatments, also known as duplex or hybrid technologies, offer new structure/property relationships in layered matrix compounds. The treatment sequence is critical. There are within reach both properties and property gradients that are impossible to achieve using the respective single treatment processes alone nor by simple addition of the effects of the single processes. Good technical progress is given by the combination of thermochemical treatment with high energy beam surface hardening, in particular electron beam hardening. After a historical survey (milestones) of the combination of thermochemical with thermal (surface) heat treatment technologies, the paper deals with the principles of the combining electron beam hardening after nitriding and vice versa , electron beam hardening before nitriding and the effects on microstructure and properties. Typical examples of industrial application are discussed. In this field of heat treatment, further development is focused on combinations of high energy beam hardening (electron or laser beam) with hard coating.     

Effect of weld form in electron beam welding on the properties of the welded joint in low carbon steels in different sections

Abstract

Twenty coupons of 100mm thickness SA 508 C13 and Fe 56.2 steels were electron beam (EB) welded to encourage industrial applications and to verify the advantages and drawbacks of the welding process. Various non-destructive tests and mechanical tests (hardness, tensile, bend, Charpy V and Pellini) were then carried out in different joint positions.

The results are more than satisfactory for the SA 508 C13 steel, whereas a reduction in toughness was observed for the Fe 56.2. Useful information concerning the qualification of the EB welding process was obtained.

This work has been carried out in co-operation between ENEA and TERNI, with the financial support of the ENEA-TIB, under a programme for the publicising of new technologies. The welds were performed by The Welding Institute, UK (TWI), whilst for some aspects concerning the characterisation of joints, useful advice was provided by the Italian Institute of Welding.