Cavity Nucleation and Growth in Nickel-Based Alloys during Creep

The number of fossil fueled power plants in electricity generation is still rising, making improvements to their efficiency essential. The development of new materials to withstand the higher service temperatures and pressures of newer, more efficient power plants is greatly aided by physics-based models, which can simulate the microstructural processes leading to their eventual failure. In this work, such a model is developed from classical nucleation theory and diffusion driven growth from vacancy condensation. This model predicts the shape and distribution of cavities which nucleate almost exclusively at grain boundaries during high temperature creep. Cavity radii, number density and phase fraction are validated quantitively against specimens of nickel-based alloys (617 and 625) tested at 700 °C and stresses between 160 and 185 MPa. The model’s results agree well with the experimental results. However, they fail to represent the complex interlinking of cavities which occurs in tertiary creep

ANALYSIS OF THE INFLUENCE OF DIFFERENT TYPES OF COATINGS ON INCREASING THE WORKING LIFE OF CONSTRUCTIONAL ELEMENTS OF THE VENTILATION MILL AND REDUCING THE WEAR OF WORKING SURFACES

Research presented in this paper analyzed the possibilities of increasing the wear resistance of the ventilation mill parts for coal grinding in power plants, analyzing with multidisciplinary research. The parts of ventilation mill are exposed in very complex working condition (high velocity of particles, presence of sand up 40% and other mineral components). Using the CFD 3D numerical simulation of multiphase flow in grinding mill, is analyzed the speed, concentration and flow angle of mixture around working parts. Analyzing the potential application of wear resistance coating on the working parts ventilation mill have goal to increase remaining working life of working elements. By analyzing the damaged parts of ventilation mill and using the numerical simulation around working elements, are selected wide pallet of wear resistance filer materials for experimental testing. To analyze possibilities to improve surface properties, the wear-resistant coatings were deposited by various technologies: manual metal arc welding, HVOF depositions and plasma welding and also are used filler materials with different chemical compositions. Samples structure is analyzed with SEM-EDS and also by measurement and distribution of hardness in the samples cross-sections. Verification of analyzed result is done by experimental testing, performing simulation of wear in ventilation mill on the samples in sandblasting machines chamber. Medium for simulating wear is quartz sand and the samples are positioned at angle 20 o. Application of this research can increase working life of parts in termoenergetic facilities, reduce the number of possible repairs and extends the period between them. This achieves significant economic effects

Generiranje tehnologije toplog istiskivanja na osnovu FEM i FMEA analize

Evaluation of risks through application of FMEA methods, give answers and conditions for an analysis which decisively affects adoption or rejection of technological and structural solutions. This is, primarily, a team-oriented dynamic method based on a multidisciplinary approach to the problem solution by FEM modeling. The primary goal is to reduce risk of errors occurring in the development and design process of new aluminium products, both in the tool design process, CAD, and in the very process of plasticity deformation by forward hot extrusion technology. It is FMEA which documents knowledge of experts in a company, and it becomes its property, gaining in value and topicality with each passing day. This was perceived by the most powerful global companies in all the fields of management technology and they solved their problems leaving nothing to circumstances or time.Procjena rizika primenom FMEA metoda daje odgovore i uslove za analizu koja presudno utječe na usvajanje ili odbacivanje tehnoloških i konstruktivnih rešenja. To je prije svega timski orijentirana dinamička metoda zasnovana na multidisciplinarnom pristupu u rješavanju problema FEM modeliranjem. Prvobitni zadatak je da smanji rizik od nastajanja grešaka prilikom procesa razvoja i projektiranja novog proizvoda od aluminijuma, kako u procesu projektiranja alata, CAD, tako i u samom procesu plastične deformacije postupkom istosmjernog istiskivanja. Upravo FMEA dokumentuje znanje eksperta u kompaniji i to postaje njena svojina koja svakim danom dobija na vrijednosti i aktuelnosti. To su najmoćnije svjetske kompanije u svim oblastima upravljanja tehnologijom odavno uočile i probleme rješavale ne prepuštajući ništa slučaju i vremenu

Numerical simulation of material flow in AA6082 during friction stir spot welding

Friction stir spot welding (FSSW) is a new solid state joining technology based on the linear friction stir welding which can be used to replace the conventional resistance spot welding as well as riveting. However, some key problems such as heat transfer and thermoplastic material flow have not yet been studied sufficiently and block the application of this advanced technology. This paper presents the coupled thermo-mechanical viscoplastic finite element formulation based on the character of FSSW. The model was calibrated by comparing temperature history between simulation results and experimental data and subsequently used to investigate the effective strain rate and material flow in joint. The temperature study showed that the simulation and experiment results coincided well with each other thus proofing the correctness of the model. The simulation results showed that the effective strain rate distribution were not uniform. The material close to the pin’s cylindrical surface had a higher effective strain rate than that of the other material. The materials in weld centre mainly experienced a compression process and the other material under the tool experienced both compression and shear process

EUROMAT 2019 Symposia on Processing

This issue of JMEP contains invited, peer-reviewed papers presented at the European Congress and Exhibition on Advanced Materials and Processes (EUROMAT 2019), held on September 1–5, 2019, in Stockholm, Sweden, in two symposia from the Area C “Processing”: C6 “Joining,” organized by Anna Zervaki (University of Thessaly, Greece), Ivan Kaban (IFW Dresden, Germany), and C. Sommitsch (Technische Universität Graz, Austria) C8 “Interface Design and Modelling, Wetting, and High-Temperature Capillarity,” organized by Pavel Protsenko (M.V. Lomonosov Moscow State University, Russian Federation), Fabrizio Valenza (CNR—ICMATE, Genoa, Italy), and Simeon Agathopoulos (University of Ioannina, Greece) The research works in the field of joining technologies, presented at the C6 symposium, concerned soldering, brazing, diffusion bonding, resistance spot welding, friction stir welding, and riveting techniques. The symposium C8 covered research topics on grain boundary wetting, surface energy of liquid metals and interfacial phenomena, considering fundamental as well as applied issues related to materials joining, and interface design. We wish to thank the authors for the written contributions and acknowledge the reviewers for their careful reading and evaluation of the manuscripts and valuable suggestions to improve the quality of the papers. We are grateful to the editor-in-chief of JMEP, Dr. Rajiv Asthana, and the ASM journal staff, including Mary Anne Fleming, senior content developer; Kate Doman, content developer (journals); and Vincent Katona, production coordinator; for the opportunity to publish the symposia contributions in this issue and for their professional and friendly support during the entire reviewing and publication process. We hope this collection will stimulate fresh thinking and promote further research on joining and interfacial phenomena

Porosity evolution and oxide formation in bulk nanoporous copper dealloyed from a copper–manganese alloy studied by in situ resistometry

The synthesis of bulk nanoporous copper (npCu) from a copper–manganese alloy by electrochemical dealloying and free corrosion as well as the electrochemical behaviour of the dealloyed structures is investigated by in situ resistometry. In comparison to the well-established nanoporous gold (npAu) system, npCu shows strongly suppressed reordering processes in the porous structure (behind the etch front), which can be attributed to pronounced manganese oxide formation. Characteristic variations with the electrolyte concentration and potential applied for dealloying could be observed. Cyclic voltammetry was used to clarify the electrochemical behaviour of npCu. Oxide formation is further investigated by SEM and EDX revealing a hybrid composite of copper and manganese oxide on the surface of a metallic copper skeleton. Platelet-like structures embedded in the porous structure are identified which are rich in manganese oxide after prolonged dealloying. As an outlook, this unique heterogeneous structure with a large surface area and the inherent properties of manganese and copper oxides may offer application potential for the development of electrodes for energy storage and catalysis

Influence of Melt-Pool Stability in 3D Printing of NdFeB Magnets on Density and Magnetic Properties

The current work presents the results of an investigation focused on the influence of process parameters on the melt-track stability and its consequence to the sample density printed out of NdFeB powder. Commercially available powder of Nd7.5Pr0.7Fe75.4Co2.5B8.8Zr2.6Ti2.5 alloy was investigated at the angle of application in selective laser melting of permanent magnets. Using single track printing the stability of the melt pool was investigated under changing process parameters. The influence of changing laser power, scanning speed, and powder layer thickness on density, porosity structure, microstructure, phase composition, and magnetic properties were investigated. The results showed that energy density coupled with powder layer thickness plays a crucial role in melt-track stability. It was possible to manufacture magnets of both high relative density and high magnetic properties. Magnetization tests showed a significant correlation between the shape of the demagnetization curve and the layer height. While small layer heights are beneficial for sufficient magnetic properties, the remaining main parameters tend to affect the magnetic properties less. A quasi-linear correlation between the layer height and the magnetic properties remanence (Jr), coercivity (HcJ) and maximum energy product ((BH)max) was found

Influences of Surface, Heat Treatment, and Print Orientation on the Anisotropy of the Mechanical Properties and the Impact Strength of Ti 6Al 4V Processed by Laser Powder Bed Fusion

The scope of this work is to provide an overview of the influences of process parameters, print orientation, and post-process treatments of Ti6AlV4 processed by laser powder bed fusion on its microstructure and physical and mechanical properties and their anisotropic behavior. To avoid the influence of changes in powder quality and ensure comparability, experiments were carried out using a single batch of virgin powder. First, characterization of the density and surface roughness was performed to optimize the process parameters utilizing design of experiment. Tensile, notched bar impact and compression test specimens were built in three different orientations: vertically, horizontally, and inclined at 45° to the build plate. Later, the influence of the staircase effect and the possible course of anisotropy from vertical to horizontal were investigated. Subsequently, heat treatments for stress relief, furnace annealing, and hot isostatic pressing were performed. In addition to as-built samples, mechanical machining and a two-step electrochemical polishing surface treatment were applied to investigate the influence of the surface roughness. With parameter optimization, a relative density of 99.8% was achieved, and surface roughness was improved over default parameters, reducing Ra by up to 7 µm. Electrochemical polishing is a viable way to decrease the surface roughness. An Ra value of 1 µm and an Rz value of 4 µm can be achieved for 45° downskin surfaces with as-built surface roughness values of Ra 24 µm and Rz 117 µm. As-built and stress-relieved conditions show little anisotropy in their yield and tensile strength (max 2.7%), but there is a strong influence of the build orientation on necking, and brittle fracture behavior is shown due to the martensitic microstructure (up to 70%). Heat treatment can increase the ductility and further decrease the strength anisotropy with both furnace annealing and hot isostatic pressing delivering similar results for tensile properties, while angled samples exhibit behavior that is closer to vertical than horizontal, indicating a non-linear change in break behavior. Electrochemical polishing increases fracture necking, and its isotropy drastically increases from 4% to over 30% compared with as-built parts, which is close to the level of the machined specimen

Microstructurally Based Modeling of Creep Deformation and Damage in Martensitic Steels

This chapter deals with modeling the microstructural evolution, creep deformation, and pore formation in creep-resistant martensitic 9–12% Cr steels. Apart from the stress and temperature exposure of the material, the input parameters for the models are as-received microstructure and one single-creep experiment of moderate duration. The models provide predictive results on deformation rates and microstructure degradation over a wide stress range. Due to their link to the underlying fundamental physical processes such as classical nucleation theory, Gibbs energy dissipation, climb, and glide of dislocations, etc., the models are applicable to any martensitic steel with similar microstructure to the presented case study. Note that we section the chapter into part 1: creep deformation and part 2: pore formation

Effect of Process Parameters and High-Temperature Preheating on Residual Stress and Relative Density of Ti6Al4V Processed by Selective Laser Melting

The aim of this study is to observe the effect of process parameters on residual stresses and relative density of Ti6Al4V samples produced by Selective Laser Melting. The investigated parameters were hatch laser power, hatch laser velocity, border laser velocity, high-temperature preheating and time delay. Residual stresses were evaluated by the bridge curvature method and relative density by the optical method. The effect of the observed process parameters was estimated by the design of experiment and surface response methods. It was found that for an effective residual stress reduction, the high preheating temperature was the most significant parameter. High preheating temperature also increased the relative density but caused changes in the chemical composition of Ti6Al4V unmelted powder. Chemical analysis proved that after one build job with high preheating temperature, oxygen and hydrogen content exceeded the ASTM B348 limits for Grade 5 titanium