Papers by Keyword: Tungsten Electrode

Abstract: The welding performance of E3, Er-W, La-W1and La-W2 was investigated in this paper. The erosion, morphological stability, U-I curve at high temperature and heavy current were studied by direct current straight polarity tungsten inert gas (DCSP TIG) welding. The morphology of erosion on the electrode surface was explored by scanning electron microscopy. The results suggest that when the welding current I₀ = 250 A,after loading 1h the mass loss of Er-W electrode was bigger than other electrodes and the tip size change of Er-W electrode was larger than others. While the mass loss of La-W1 was least and the tip size of La-W1 was relatively stable. The metallographic structure of the electrode tips showed that the recrystallized grain size of La-W1 was much smaller than others,which showed that metal rhenium can refine recrystallized grains of material and improve the electron emission performance. As a result, La-W1 electrode had superiority in welding performance.

Abstract: Autogenous gas tungsten arc welding (GTAW) using different non-consumable pure tungsten electrodes (EWP) from eight different manufacturers was performed on aluminum alloy 5083 samples. Due to the limited literatures of how tungsten microstructure may affect the weld quality, this paper attempts to investigate the change in microstructure of tungsten electrode after welding compared to the original microstructure in as-received condition. The scanning electron micrograph results reveal different grain shapes and sizes and also different grain growth rate during welding. It was found that the ability to control the grain growth or limit grain size within the balled end of pure tungsten electrode during aluminum welding plays a very important role in determining the quality of the electrode and how long the electrode would last.

Abstract: The paper presents the results of studies aimed at justifying and developing the ways and means of cylindrical parts made of hardenable alloys surface hardening by heating of the electric arc between the inert electrode and the element. The shapes of electrode sharpening and the position of the electrode relative to the element are substantiated. The sequence of surface hardening operations is revealed and the critical rate of cooling is determined and its value is proved with numerical experiments. It was necessary to develop a program for calculating temperature fields in details, with a difference-differential scheme obtained from a combination of explicit and implicit schemes being developed for the first time. A number of investigations were conducted to determine the mechanical properties, the residual stresses, the fatigue resistance, the hardness and the microstructure of hardened layers. As a result, the surface hardening technology is recommended for reconditioning and manufacturing cylindrical machine elements.

Abstract: The paper presents the results of the studies devoted to justification and development of methods and means of high-speed thin layer coating. It outlines the layer conditions formation, as well as the requirements for the individual components and surfacing installation assemblies. The following equipment items are designed and manufactured for the implementation of the developed coating processes: surfacing rack, feeding device rotating filler, surfacing head-die and others. The paper presents the completely temperature pattern detailed calculation program with differential-difference scheme-line obtained from a combination of explicit and implicit schemes. The mechanical properties, residual stress, fatigue strength, hardness and microstructure of the coating, etc. have been undertaken as well. The paper recommends the technology to restore worn surfaces of the cylindrical parts with little wear and tear (up to 0.3 mm) and to impart special physical and mechanical properties of the manufactured machine parts surfaces.

Abstract: The electrode is widely used in TIG for its characteristics of high melting point and low work function. This paper provides a general classification of rare earth tungsten electrode, and briefly introduces its development course. At the same time, the emission properties, processing and application of the rare-earth tungsten electrode are reviewed in this paper which briefly overviews the status quo and the developments in research on the Tungsten electrodes. This paper also forecasts the development tendency and application prospect of the electrodes, aiming at providing valuable reference for the research and promotion on rare-earth tungsten electrode materials.

Abstract: The forming of rare earth tungsten electrode is difficult. The mechanical properties and microstructure evolution of several φ2.4mm rare earth tungsten electrodes were studied by SEM, EBSD and TEM technology. The static tensile test was carried out in different pulse current density, and the temperature of the samples in processing was measured with K thermocouple. The results showed that the sample had the best elongation of 8.87% when the pulse current density was 800 A/mm². SEM analysis showed that the second phase was broken and some of them were spheroidized in electric sample. It is indicated that the electric pulse accelerated the formation of [110] texture and the low angle boundaries decreased by EBSD, and TEM analysis revealed that the dislocation cell wall was thinner and the adjacent cell got merged in electric sample.

Abstract: In this paper, the influence of different contents of rare earth oxides of tungsten electrodes on the welding performance has been studied. Tungsten inert gas weld was carried out on 1060 aluminum plate, using different contents of rare earth oxides of tungsten electrodes. The content of CeO₂ are 2% and 4%, the content of composite rare earth oxides (La₂O₃: CeO₂: Y₂O₃ = 1:1:3) is 4%. The mechanical properties of these welded joints were investigated. The results indicated that the loss of the CeO₂ content of 4% electrode weight was the maximum. The arc stability of the three kinds of tungsten electrodes was good. The arc static characteristic curve of the composite rare earth—tungsten electrode was lower than that of the cerium—tungsten electrode. The loss of rare earth oxides of electrode had little effect on the mechanical properties of welded joints.

Abstract: The welding which is used to seal the hole on the nuclear fuel rod is performed in a chamber which is filled with high-pressure helium. Experiments were done with different current and distance of tungsten and the end plug. Each current curve and voltage curve was analyzed. The results show that the effect of increasing the welding current or shortening the distance between the tungsten electrode and the end plug on the arc is that arc voltage is smaller and the arc stability is improved. The plan that positioning head is composed of two parts was put forward to control the fuel rod positioning accuracy. By means of properly choosing and controlling the parameters, the quality of welding is certainly improved and the rate of rejection is declined.

Abstract: Lifetime of tungsten electrodes for fusing was investigated in relation to their microstructure. Tungsten electrodes with two types of microstructures (recrystallized equi-axed and unrecrystallized fibrous) were subjected to repeated welding tests where work material was a tough pitch copper. Surface appearance of the electrodes after the test was observed with an SEM. Circumferential edge cracks were observed in the equi-axed electrode, which were presumed to be initiated by plastic flow of the work material. Although cracks were formed in the center of both types of electrodes, the total length of them is longer in the equi-axed electrode. Therefore, the lifetime was expected to be longer in the fibrous electrode than the equi-axed.

Abstract: Study of current attachment at thermionic cathode for TIG arc at atmospheric pressure is attempted from numerical calculations of arc-electrodes unified model. The calculations show that the maximum temperature of arc plasma close to the cathode tip for W-2% ThO2 reaches 19,000 K and it is the highest value in comparison with the other temperatures for W-2% La2O3 and W-2% CeO2, because the current attachment at the cathode tip is constricted by a centralized limitation of liquid area of ThO2 due to its higher melting point. The calculations also show that, in cases of W- 2% La2O3 and W-2% CeO2, the liquid areas of La2O3 and Ce2O3 are widely expanded at the cathode tip due to their lower melting points and then produce uniform current attachments at the cathode. It is concluded that the current attachment at thermionic cathode is strongly dependent on work function, melting point and Richardson constant of emitter materials.