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  • 1.
    Fisk, Martin
    et al.
    Materials Science and Applied Mathematics, Faculty of Technology and Society, Malmö University.
    Ion, John
    Division of Materials Science, Malmö University.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Flow stress model for IN718 accounting for evolution of strengthening precipitates during thermal treatment2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 82, p. 531-539Article in journal (Refereed)
    Abstract [en]

    A flow stress model describing precipitate hardening in the nickel based alloy Inconel® 718 following thermal treatment is presented. The interactions between precipitates and dislocations are included in a dislocation density based material model. Compression tests have been performed using solution annealed, fully-aged and half-aged material. Models were calibrated using data for solution annealed and fully-aged material, and validated using data from half-aged material. Agreement between experimental data and model predictions is good.

  • 2. Ion, John
    Laser beam welding of wrought aluminium alloys2000In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 5, no 5, p. 265-276Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    Ion, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Laser processing of engineering materials2002In: Recent Research Developments in Materials Science: Vol. 3, Research Signpost, 2002, p. 529-549Chapter in book (Other academic)
  • 4.
    Ion, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Laser processing of engineering materials: principles, procedure and industrial application2005Book (Other academic)
  • 5. Ion, John
    Laser transformation hardening2002In: Surface Engineering, ISSN 0267-0844, E-ISSN 1743-2944, Vol. 18, no 1, p. 14-31Article in journal (Refereed)
    Abstract [en]

    Surface hardening by inducing phase transformations through the heating effect of a laser beam was one of the first laser based fabrication methods to be commercialised, in the early 1970s. However, its industrial acceptance has been limited, in comparison with other laser based processes such as cutting, welding, and marking. The reasons lie in a lack of knowledge concerning the process, and the large number of more familiar surface hardening processes that are commercially available. Within the last five years important developments have taken place in the technology of laser sources, optics, and software, which now enable the process to be viewed more favourably against competing processes. More suitable laser sources, such as multikilowatt Nd:YAG and diode lasers, and beam delivery optics have been developed. Sophisticated system control software now enables mathematical process models to be integrated into production systems. Computer aided design (CAD) software enables products to be redesigned, and life cycle performance and process comparisons can be evaluated rapidly. Thus automated laser hardening systems are now becoming available, suitable for treating components of widely varying size and shape. The requirements of codes for hardening can be met in a wide range of steels and cast irons. This review summarises the state of the art in the process, industrial practice, properties of hardened materials, and the software now available, and describes the areas in which work is needed to extend the industrial application of the process.

  • 6.
    Ion, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Modelling the microstructural changes in steels due to fusion welding1984Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Theoretical, physically-based models of fusion welding are developed, and calibrated using experimental data from practical welds. The following heat-affected zone phenomena are investigated: grain growth, precipitate dissolution and coarsening, martensite formation and hardness. A model is also developed to describe the effects of the welding arc and their dependence on welding conditions. All calculations are carried out using a microcomputer which readily allows the influence of a large number of material and welding variables to be taken into account. The results are presented as read-outs in the form of various types of Welding Process Diagrams, these providing information on weld geometry, H.A.Z. microstructure and hardness in a form understandable to the welding metallurgist and engineer alike. In addition, Implant Testing Diagrams are developed, based on similar modelling, which help to exactly locate the notch with respect to the grain growth zone and weld process. Diagrams can be constructed showing microstructural variation over a wide range of energy inputs corresponding to different welding processes, or for a particular process showing weld geometry and providing a physical picture of the weld. The programs are written such as to allow easy interaction between the operator and computer concerning choice of welding parameters, steel composition etc., and the storage of material data which can be readily called up by the operator. It is thus shown that the diagrams can be used to help optimize welding conditions, as well as supply information on the H.A.Z. microstructure and hardness.

  • 7. Ion, John
    et al.
    Ainsdahl, L.M.
    SINTEF.
    A PC-based system for procedure developement in laser transformation hardening1997In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 65, no 1-3, p. 261-267Article in journal (Refereed)
    Abstract [en]

    A PC-based software package has been developed which facilitates the generation of procedures for laser transformation hardening. The package comprises a model-based process simulation module, a graphical user interface based on a standarized parameter record, a database of completed procedures, and a processing cost analysis. Analytical models of heat flow and phase transformations are used to predict the depth of the transformed zone and the maximum hardness developed, in terms of the principal process variables (the laser beam parameters and material properties). Good agreement between experimental data and model predictions is demonstrated for a range of alloy steels. Realistic sets of processing parameters can thus be obtained for experimental evaluation, reducing the amount of trial-and-error testing significantly. Archived procedures can be retrieved for editing and further development. Processing costs can be compared readily with those for conventional surface-hardening techniques.

  • 8.
    Ion, John
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ashby, Michael F.
    University of Cambridge.
    Weldability charts for constructional steels2012In: 6th EEIGM International Conference Advanced Materials Research: 7th and 8th November, 2011 EEIGM, Nancy, France, Bristol: IOP Publishing Ltd , 2012Conference paper (Refereed)
    Abstract [en]

    The weldability of materials is still a poorly understood concept; a quantitative assessment remains elusive. The variables associated with welding are reduced here into two groups - processing parameters and material properties - from which two characteristic indices are defined and used as the basis of weldability charts. For the case of constructional steels, a carbon equivalent characterises both heat affected zone hardenability and the maximum hardness developed after solid state phase transformations. The welding process is characterised by its energy input. A mathematical model is used to establish relationships between the indices, which are displayed on charts as contours of microstructure and hardness.

  • 9.
    Ion, John
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Easterling, K.E.
    Luleå tekniska universitet.
    Ashby, M.F.
    Engineering Department, Cambridge University.
    A second report on diagrams of microstructure and hardness for heat-affected zones in welds1984In: Acta Metallurgica, ISSN 0001-6160, Vol. 32, no 11, p. 1949-1962Article in journal (Refereed)
    Abstract [en]

    The paper improves and extends kinetic models to include: precipitate coarsening; the use of semi-empirical equations including carbon-equivalence to predict microstructure and hardness; a comparison between the theory and data obtained from different types of real welds; and an alternative, more easily used diagram.

  • 10.
    Ion, John
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Easterling, Kenneth E.
    Luleå tekniska universitet.
    Computer modelling of weld-implant testing1985In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 1, no 5, p. 405-411Article in journal (Refereed)
    Abstract [en]

    A theoretical model is developed for determining the optimum notch position in an implant test used for predicting the susceptibility to hydrogen cracking during welding. Using a microcomputer for processing the equations for weld-bead geometry and heat flow during welding, a microstructural cross-section, with the notch positioned at the center of the grain-growth zone, and an implant testing diagram, showing the notch position and microstructure as a function of welding parameters, can be generated. A single bead-on-plate weld is used to determine the unknown kinetic and geometrical constants in the equations. It is shown that notch position is very sensitive to the type of welding process employed and that implant diagrams thus can be used to position the notch with greater reliability and hence reduce the scatter in the fracture loads measured in this test

  • 11. Ion, John
    et al.
    Kauppila, J.
    Metsola, P.
    Laser-based fabrication: opportunities for novel design and manufacturing1999In: 7th NOLAMP Conference: 7th Nordic Conference on Laser Processing of Materials ; [Lappeenranta, 1999] / [ed] Veli Kujanpää; John Ion, Lappeenranta: Lappeenrannan teknillinen korkeakoulu , 1999, p. 38-47Conference paper (Refereed)
  • 12.
    Ion, John
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kokkonen, J.
    Lappeenranta University of Technology.
    A comparison of gas tungsten arc and CO2 laser beam welding of AA20242001In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 13, no 2, p. 79-83Article in journal (Refereed)
    Abstract [en]

    Mechanical fastening methods are used extensively to join aluminum alloys, particularly in the aerospace industries. Laser welding provides the possibility of a high productivity single-step process, with the added benefit of potential weight savings of about 10% in comparison with riveting. However, the weldability of many aluminum aerospace alloys is generally considered to be low, and little data are currently available. A procedure for CO2 laser welding of the alloy AA2024 is developed, with the use of 2319 filler wire. Weld property data are shown to achieve the requirements for the most stringent quality level of the current European workmanship standard for laser-welded joints in aluminum. Hardness and tensile strength properties are shown to be similar to those of gas tungsten arc (GTA) welds. The fatigue strength of GTA welds is superior to that of laser welds in the as-welded condition, but when the weld bead is machined flush with the plate surface the difference is reduced. The laser welds achieved the requirements of recommendations produced by the International Institute of Welding for single-sided welding of aluminum alloys. The quality of the weld toe is shown to have the greatest effect on fatigue strength.

  • 13. Ion, John
    et al.
    Moisio, T.
    Lappeenranta University of Technology.
    Paju, M.
    Lappeenranta University of Technology.
    Johansson, J.
    Lappeenranta University of Technology.
    Laser transformation hardening of low alloy hypoeutectoid steel1992In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 8, no 9, p. 799-803Article in journal (Refereed)
    Abstract [en]

    The principles of laser transformation hardening were investigated using a low alloy special steel having a microstructure of pearlite and proeutectoid ferrite. Temperature fields and phase transformations were modelled. Particular attention was paid to increases of the Ac1 and Ac3 transformation temperatures owing to the rapid thermal cycles produced by laser heating. Dissolution of proeutectoid ferrite is shown to control the formation of a homogeneous hardened case. Experimental data are in good agreement with the predictions of the model. A diagram was constructed which describes the case geometry and microstructure in terms of the process variables and is an aid to optimising practical processing parameters. The models are flexible and may be used for laser transformation hardening of other ferrous alloys having inhomogeneous microstructures.

  • 14. Ion, John
    et al.
    Moisio, T.
    Lappeenranta University of Technology.
    Pedersen, T.F.
    Danish Corrosion Centre.
    Sørensen, B.
    Danish Corrosion Centre.
    Hansson, C.M.
    Danish Corrosion Centre.
    Laser surface modification of a 13.5% Cr, 0.6% C steel1991In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 26, no 1, p. 43-48Article in journal (Refereed)
    Abstract [en]

    A 13.5% Cr, 0.6% C steel, with an initial microstructure of chromium carbides in a ferrite matrix, was heat-treated by scanning a high-power laser beam over the surface. The aim was to compare the physical and chemical properties produced by this type of selective surface treatment with those resulting from a conventional furnace desensitization and quench-hardening heat treatment. Surface heating homogenized the carbon originally bound in the carbides sufficiently to produce martensite, giving hardening to levels comparable with a conventional heat treatment. Chromium-rich zones, carbides and retained austenite were also detected in the heated microstructure. Surface melting produced complete homogenization of both carbon and chromium, which resulted in the retention of large amounts of austenite in the microstructure on cooling to room temperature. Subsequent refrigeration at - 196 °C transformed some of the austenite to martensite. Pitting corrosion and local reductions in hardness were observed adjacent to treated areas under certain conditions, due to precipitation of secondary carbides and elevated tempering, respectively.

  • 15. Ion, John
    et al.
    Salminen, A.S.
    LaserPlus Oy, Riihimäki.
    Sun, Z.
    Gintic Institute of Manafacturing Technology.
    Process diagrams for laser beam welding of carbon manganese steels1996In: Welding Journal, ISSN 0043-2296, Vol. 75, no 7, p. 225-Article in journal (Refereed)
    Abstract [en]

    Diagrams are presented which illustrate the ranges of process variables that can be used to produce acceptable laser welds in carbon manganese steels. The most practical type uses axes of beam power and welding speed. An empirical operating window is displayed, which describes the limits of full joint penetration welding for a particular steel and plate thickness. Theoretical contours of heat-affected zone (HAZ) hardness, established using analytical models, are also displayed on the diagram. Appropriate combinations of laser beam power and welding speed can thus be selected. A more comprehensive diagram uses axes of carbon equivalent and absorbed laser beam energy, on which theoretical HAZ hardness contours are displayed. The effects of changes in steel composition and welding variables on HAZ hardness can thus be assessed. Model results agree well with experimental data, as well as more sophisticated predictive methods. The diagrams provide guidance on the selection of steel composition and beam parameters during the initial stages in the development of procedures for laser welding of carbon manganese steels.

  • 16. Ion, John
    et al.
    Shercliff, H.R.
    University of Cambridge.
    Ashby, M.F.
    University of Cambridge.
    Diagrams for laser materials processing1992In: Acta Metallurgica et Materialia, ISSN 0956-7151, Vol. 40, no 7, p. 1539-1551Article in journal (Refereed)
    Abstract [en]

    An analytical heat flow model is used to identify dimensionless parameter groups which determine the temperature field produced in a material by a scanning laser beam. The groups are used to plot experimental data for metallic alloys on a processing diagram for a range of continuous CO2 laser treatments. Practical operating regions for each type of treatment are thus identified, which coincide with those predicted using the heat flow model. The model is extended in order to construct more detailed diagrams for transformation hardening, surface melting and keyhole welding, which quantify the depth of treatment. By using realistic estimates of certain poorly-known process variables, good agreement is observed between measured and predicted data. Methods for optimising processing parameters with respect to various criteria are presented for transformation hardening. The diagrams, which are constructed on a personal computer, are a useful tool for summarising current data, optimising practical processing parameters, and assessing the potential of novel laser treatments on new materials

  • 17.
    Jansson, A.
    et al.
    VTT Technical Research Centre of Finland, Espoo.
    Ion, John
    Kujanpää, V.
    Co2 and Nd:YAG laser cladding using Stellite 62003In: Surface Modification, Cladding, and Protoyping, Bellingham: SPIE - International Society for Optical Engineering, 2003, p. 475-480Conference paper (Refereed)
  • 18. Kokkonen, J.
    et al.
    Ion, John
    CO2 laser welding of the aluminium aerospace alloy AA20241999In: 7th NOLAMP Conference: 7th Nordic Conference on Laser Processing of Materials ; [Lappeenranta, 1999] / [ed] Veli Kujanpää; John Ion, Lappeenranta: Lappeenrannan teknillinen korkeakoulu , 1999, p. 418-429Conference paper (Refereed)
  • 19. Kujanpää, Veli
    et al.
    Ion, John
    7th NOLAMP Conference: 7th Nordic Conference in laser processing of materials1999Collection (editor) (Other academic)
  • 20.
    Pfluger, D.
    et al.
    CSIRO, Manufacturing Science and Technology.
    Harris, D.
    CSIRO, Manufacturing Science and Technology.
    Ion, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    The application of optical signal detection for characterizing transitions during laser beam welding2002In: Congress proceedings: Laser Materials Processing Conference [and] Laser Microfabrication Conference [presented at] ICALEO 2002, 21st International Congress on Applications of Lasers & Electro-Optics, October 14 - 17, 2002, Double Tree Paradise Valley Resort, Scottsdale, Arizona, USA / / [ed] Eckhard Beyer, Orlando, Fla: Laser institute of America , 2002Conference paper (Refereed)
    Abstract [en]

    Optical signals generated in the interaction zone between an Nd:YAG laser beam and an aluminum alloy have been investigated, in order to gain an appreciation of their potential for use in adaptive control systems for laser processing. A system has been developed that enables such signals to be recorded and analyzed. The laser beam welding process has been monitored, from the first visible signs of surface damage through to full penetration of the work piece, by linearly increasing the laser power during a melt run performed with a constant traverse rate. Trials were carried out on samples of the aluminum alloys AA5083 and AA5005 with various surface preparations and with a variety of sensor configurations. The characteristics of the resultant welds were established by using optical and scanning electron microscopy on transverse weld sections. The signals measured were consistent with well-defined characteristic modes of interaction. The effects of surface penetration, surface reflectance and weld pool curvature on the signals produced are noted and discussed. A fundamental understanding of the potential for optical signals to be used for on-line characterization of laser-material interactions was achieved through analysis and validation of the data captured. The methods used are sufficiently generic to be applied to other materials and laser-based processes.

  • 21.
    Stjernberg, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ion, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindblom, B.
    LKAB.
    Lab scale study of the depletion of mullite/corundum-based refractories trough reaction with scaffold materials2011In: IOP Conference Series: Materials Science and Engineering: Symposium 16, 2011 (222001-222031) Innovation in Refractories and Traditional Ceramics, IOP Publishing Ltd , 2011, Vol. 18, article id 222004Conference paper (Refereed)
    Abstract [en]

    To investigate the mechanisms underlying the depletion of mullite/corundum-based refractory bricks used in rotary kilns for iron ore pellet production, the reaction mechanisms between scaffold material and refractory bricks have been studied on the laboratory-scale. Alkali additions were used to enhance the reaction rates between the materials. The morphological changes and active chemical reactions at the refractory/scaffold material interface in the samples were characterized using scanning electron microscopy (SEM), thermal analysis (TA) and X-ray diffraction (XRD). No reaction products of alkali and hematite (Fe2O3) were detected; however, alkali dissolves the mullite in the bricks. Phases such as nepheline (Na2OAl2O32SiO2), kalsilite (K2OAl2O32SiO2), leucite (K2OAl2O34SiO2) and potassium β-alumina (K2O11Al2O3) were formed as a consequence of reactions between alkali and the bricks.

  • 22.
    Stjernberg, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ion, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Nordin, Lars-Olof
    LKAB.
    Lindblom, Bo
    LKAB.
    Odén, Magnus
    Linköping University, Division of Nanostructured Materials.
    Extended studies of degradation mechanisms in the refractory lining of a rotary kiln for iron ore pellet production2012In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 32, no 8, p. 1519-1528Article in journal (Refereed)
    Abstract [en]

    Changes, over a period of 8 years, in the chemical composition and morphology of deposit and lining materials in a production rotary kiln for iron ore pellet manufacture are described. The following have been studied: two types of refractory brick used as lining material; deposited chunk materials from the lining; the interaction zones between deposits and linings. Morphological changes at the deposit/lining interface, and the active chemical reactions, are established. Larger hematite grains in the deposit material (5–50 μm) primarily remain at the original deposit/lining interface. The remainder penetrates fissures, voids and brick joints, forms a laminar structure with corundum from the bricks, and migrates in grains in the lining material. Potassium penetrates more deeply into the bricks than hematite, resulting in the formation of kalsilite, leucite and potassium β-alumina, which contribute to degradation of the lining.

  • 23.
    Stjernberg, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Isaksson, Ola
    LKAB.
    Ion, John
    The grate-kiln induration machine: history, advantages, and drawbacks, and outline for the future2015In: The Journal of The Southern African Institute of Mining and Metallurgy, ISSN 2411-9717, Vol. 115, no 2, p. 137-144Article in journal (Refereed)
    Abstract [en]

    Iron ore pellets are a preferred feedstock for ironmaking. One method used for pelletizing is the grate-kiln process, first established in 1960. During the past decade, the establishment of new grate-kiln plants has increased rapidly, especially in China, and new constructors of pellet plants have started to operate in the market. It is well known that the grate-kiln method yields a superior and more consistent pellet quality compared with the straight-grate process. However, certain issues exist with the grate-kiln plant, which are discussed here, together with proposed practical solutions.

  • 24.
    Stjernberg, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Nordin, Lars-Olof
    LKAB Research and Development, Metlab.
    Ion, John
    Malmö högskola.
    Evaluation of refractory castables and coatings used in the pre-heat zone of a grate-kiln for iron ore pellet production2015In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 42, no 4, p. 274-281Article in journal (Refereed)
    Abstract [en]

    Iron ore pellets are a prepared burden material for ironmaking that are commonly sintered in a grate kiln furnace system. Deposited material can adhere in chunks to localised regions of the lining of such furnaces, causing lining depletion. Such deposits consist mainly of iron oxides, but alkali, alkaline earth and other oxides formed from disintegrated pellets and fly ash may also be present. In order to investigate methods of preventing such formations, tests have been performed using several different castables and coatings. Samples of liner castables with and without coatings, installed in an industrial furnace, were collected after 6 and 24 months in production use, and characterised using scanning electron microscopy to identify the materials, characterise morphological changes at the deposit-coating-lining interface, and to determine the active chemical reactions. An Al2O3 based coating applied to one of the fields was found to be in good condition after 6 months in use, but no traces of the coating were observed after 24 months in use. A carbon phosphate based coating was not intact after 6 months in use; it was probably burned-up as a result of the oxidising atmosphere. Hematite grains from the deposit material remained at the original deposit-lining interface, while calcium migrated further into the lining.

  • 25.
    Stjernberg, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Olivas-Ogaz, M.A.
    Luleå tekniska universitet.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ion, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindblom, B.
    LKAB.
    Laboratory scale study of the degradation of mullite/corundum refractories by reaction with alkali-doped deposit materials2013In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 39, no 1, p. 791-800Article in journal (Refereed)
    Abstract [en]

    Refractory bricks based on mullite and corundum, commonly used in rotary kilns for iron ore pellet production, and depositmaterial from an iron ore pellet production kiln, were used in laboratoryscale tests to investigate refractory/depositreactions and the infiltration of deposit components into the refractory bricks. The materials tested were in both monolithic form and in the form of powder. Alkali metal carbonates (containing sodium and potassium) were used as corrosive agents, to increase reaction kinetics. The morphological changes and active chemical reactions at the refractory/deposit interface in the samples were characterized by scanning electron microscopy. X-ray diffraction showed that alkali metals react with the mullite in the bricks, this being more pronounced in the case of sodium than potassium. Phases such as nepheline (Na2O·Al2O3·2SiO2), kalsilite and kaliophilite (both K2O·Al2O3·2SiO2), and leucite (K2O·Al2O3·4SiO2) were formed as a consequence of reactions between alkali metals and the refractory bricks. The formation of these phases causes volume expansions of between 20% and 25% in the brick materials, which accelerate degradation.

  • 26.
    Sun, Z.
    et al.
    Lappeenranta University of Technology.
    Ion, John
    Laser welding of dissimilar metal combinations1995In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 30, no 17, p. 4205-4214Article in journal (Refereed)
    Abstract [en]

    The ability to manufacture a product using a number of different metals and alloys greatly increases flexibility in design and production. Properties such as heat, wear and corrosion resistance can be optimized, and benefits in terms of production economics are often gained. Joining of dissimilar metal combinations is, however, a challenging task owing to the large differences in physical and chemical properties which may be present. Laser welding, a high power density but low energy-input process, provides solutions to a number of problems commonly encountered with conventional joining techniques. Accurate positioning of the weld bead, rapid heating and cooling, low distortion, process flexibility, and opportunities for product redesign are its principal characteristics. The review describes the principles underlying laser welding of dissimilar metal combinations and highlights the above benefits in a number of practical applications. It is concluded that there is potential for its application in many industrial sectors.

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