The aim of this master’s thesis was to evaluate cold spray technologies as an alternative method of repairing contact surfaces of parts, especially made of high-alloy manganese steels, to choose a suitable system of materials and to analyze the properties and structure of the produced coating. The thesis presents the basic of the mechanism of cold spray deposition, the described influence of basic process parameters on the structure and properties of metal coatings. Performed analysis of chemical composition, structure, porosity, hardness and strength of AISI H13 steel coating on a high-alloy manganese steel substrate. The described dependence of the structure and properties of a given coating on the heat treatment regime.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19307号 / 工博第4104号 / 新制||工||1633(附属図書館) / 32309 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 中村 裕之, 教授 邑瀬 邦明 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Particle-laden supersonic jets impinging on a flat surface are of interest to cold gas-dynamic spray technology. Solid particles are propelled to a high velocity through a convergent-divergent nozzle, and upon impact on a substrate surface, they undergo plastic deformation and adhere to the surface. For given particle and substrate materials, particle velocity and temperature at impact are the primary parameters that determine the success of particle deposition. Depending on the particle diameter and density, interactions of particles with the turbulent supersonic jet and the compressed gas region near the substrate surface can have significant effects on particle velocity and temperature. Unlike previous numerical simulations of cold spray, in this dissertation we track solid particles in the instantaneous turbulent fluctuating flow field from the nozzle exit to the substrate surface. Thus, we capture the effects of particle-turbulence interactions on particle velocity and temperature at impact. The flow field is obtained by direct numerical simulations of a supersonic rectangular particle-laden air jet impinging on a flat substrate. An Eulerian-Lagrangian approach with two-way coupling between solid particles and gas phase is used. Unsteady three-dimensional Navier-Stokes equations are solved using a six-order compact scheme with a tenth-order compact filter combined with WENO dissipation, almost everywhere except in a region around the bow shock where a fifth-order WENO scheme is used. A fourth-order low-storage Runge-Kutta scheme is used for time integration of gas dynamics equations simultaneously with solid particles equations of motion and energy equation for particle temperature. Particles are tracked in instantaneous turbulent jet flow rather than in a mean flow that is commonly used in the previous studies. Supersonic jets for air and helium at Mach number 2.5 and 2.8, respectively, are simulated for two cases for the standoff distance between the nozzle exit and the substrate. Flow structures, mean flow properties, particles impact velocity and particles deposition efficiency on a flat substrate surface are presented. Different grid resolutions are tested using 2, 4 and 8 million points. Good agreement between DNS results and experimental data is obtained for the pressure distribution on the wall and the maximum Mach number profile in wall jet. Probability density functions for particle velocity and temperature at impact are presented. Deposition efficiency for aluminum and copper particles of diameter in the range 1 micron to 40 microns is calculated. Instantaneous flow fields for the two standoff distances considered exhibit different flow characteristics. For large standoff distance, the jet is unsteady and flaps both for air (Mach number 2.5) and for helium (Mach number 2.8), in the direction normal to the large cross-section of the jet. Linear stability analysis of the mean jet profile validates the oscillation frequency observed in the present numerical study. Available experimental data also validate oscillation frequency. After impingement, the flow re-expands from the compressed gas region into a supersonic wall jet. The pressure on the wall in the expansion region is locally lower than ambient pressure. Strong bow shock only occurs for small standoff distance. For large standoff distance multiple/oblique shocks are observed due to the flapping of the jet. The one-dimensional model based on isentropic flow calculations produces reliable results for particle velocity and temperature. It is found that the low efficiency in the low-pressure cold spray (LPCS) compared to high-pressure cold spray (HPCS) is mainly due to low temperature of the particles at the exit of the nozzle. Three-dimensional simulations show that small particles are readily influenced by the large-scale turbulent structures developing on jet shear layers, and they drift sideways. However, large particles are less influenced by the turbulent flow. Particles velocity and temperature are affected by the compressed gas layer and remain fairly constant in the jet region. With a small increase in the particles initial temperature, the deposition efficiency in LPCS can be maximized. There is an optimum particle diameter range for maximum deposition efficiency. / Ph. D.

Abstract This thesis pursues to evidence that it is possible to get information on the behaviour of a complex chemical process by data-based analysis, even though the accurate reaction chemistry is not known. In the hydrometallurgical zinc production process, metallic zinc is produced by reducing it from aqueous solution. The essential part of the process is the purification of zinc sulphate solution, where all elements nobler than zinc are removed by deposition from the solution. These elements lower the efficiency of the electric current drastically and cause zinc dissolution even in the smallest amounts. Process monitoring supplies a remarkable amount of on-line measurement data and analysis information. This makes it possible to use data-based methods for the evaluation of deposition reactions. The purpose of this thesis was not to specify reaction equations, but to evaluate which of the known reactions will occur in different process conditions. This was done by diagnosing the purification process of zinc sulphate solution and by combining measurement information with reaction models. An increased understanding of process stability also affects solution purification costs. The results gave new information about the purification process of zinc sulphate solution and its accelerating and decelerating components. The second target was to develop a modular, model-free method of signal validation and estimation, suitable for implementation in the control system in the form of a simple, configurable algorithm. Combining measurements confidence level-based information with fuzzy logic provides a compact system that is easily implemented in the process automation system. The algorithm that was developed was tested in a direct leaching process, where the combination of fast on-line sensors and accurate reference measurement was needed. Measurement data came from an operational zinc plant, so the amount of factory testing was strictly limited. Data evaluation was based on long-term variations in process conditions, possible disturbances and breakdowns of the measurement devices. / Tiivistelmä Tämä väitöskirja pyrkii osoittamaan, että monimutkaisen kemiallisen prosessin toiminnasta voidaan saada tietoa prosessimittauksista laskettujen tunnuslukujen ja niihin vaikuttavien tekijöiden mallintamisen avulla, vaikka reaktioiden tarkkaa kemiaa ei tunneta. Tutkimuskohteena käytetyssä sinkin hydrometallurgisessa valmistuksessa tärkeimpiä osaprosesseja ovat liuotus, haitta-aineiden saostus ja elektrolyyttinen pelkistys. Haitta-aineiden saostaminen tapahtuu reagenssien avulla. Reaktiossa on mukana sekä kiinteä, nestemäinen ja kaasufaasi, joiden välisiä reaktiota ja yhteisvaikutusta ei pystytä tarkasti tutkimaan ja määrittämään. Prosessista on kuitenkin saatavilla huomattava määrä mittaus- ja analyysitietoa, joten eri saostusreaktioihin vaikuttavien tekijöiden vaihtelua voidaan tutkia datapohjaisesti. Tutkimuksen tarkoituksena oli selvittää, kuinka suurelta osin tunnetut reaktiot toteutuvat ja kuinka suuri on se osuus reaktioista, joita ei pystytä selittämään. Lisäksi eri luotettavuusasteisen mittaustiedon yhdistämisellä pyrittiin lisäämään mittaustiedon luotettavuutta ja tuottamaan operaattoreille entistä käyttökelpoisempaa informaatiota prosessin tilasta. Tätä varten kehitettiin helposti käyttökohteen mukaan adaptoitava laskenta-algoritmi, joka tuottaa mittaustietoihin perustuvan estimaatin. Estimaatin toimintaa testattiin suoraliuotusprosessissa, josta oli saatavilla sekä on-line mittauksia että tarkkoja referenssimittauksia. Tutkimusaineistona käytettiin Kokkolan sinkkitehtaalta saatavaa mittausdataa. Mittausaineisto työhön on suurimmaksi osaksi peräisin toimivasta tehdasprosessista, joten tuotannolliset seikat ovat voimakkaasti rajoittaneet prosessikokeiden tekoa. Työssä onkin turvauduttu pitkällä aikavälillä tapahtuneiden muutosten sekä mahdollisten prosessihäiriöiden ja analysaattorien vikaantumisten aiheuttamien muutosten analysointiin. Tilastollisen analysoinnin avulla selvitettiin, tapahtuuko prosessiparametrien välisissä riippuvuuksissa muutoksia eri mittausaineistojen välillä. Tutkimustulosten perusteella pystytään pitämään saostusprosessi paremmin optimaalisella toiminta-alueella. Kehitetty "optimaalisen estimaatin" laskenta-algoritmi on asennettu toimimaan tehtaan prosessinohjaustietokantaan.

High temperature gas cooled nuclear reactors often make use of Tristructural Isotropic (TRISO) coated fuel particles. In these particles, a layer of silicon carbide plays the key role of providing mechanical strength and acting as a diffusion barrier so preventing the release of fission products. TRISO particles are produced by a chemical vapor deposition (CVD) process in a spouted bed coater. Operating conditions of chemical vapor deposition processes are known to influence the properties of the deposited material. In the case of silicon carbide deposited by pyrolysis of methyltrichlorosilane (MTS) in a hydrogen atmosphere, process parameters that may influence the properties of the silicon carbide deposited include deposition temperature, MTS concentration and hydrogen flow rates. In this study the coating process was investigated using a laboratory scale spouted bed CVD coater. In all the test work conducted, carbon coated zirconia particles were used as a starting material. Only silicon carbide was deposited during these trials. Process parameters investigated were temperature, MTS concentration and hydrogen flow rate. The range investigated was 1250 °C to 1550 °C for temperature, 0.5 % to 2.5 % for MTS concentration and 10.0 l.minute-1 to 15.0 l.minute-1 for hydrogen flow. This covered the range that is typically used for small-scale production coaters. Two different gas inlet configurations, a conventional water cooled inlet and an inlet without any cooling, were used in the investigation. Properties of the coating process, such as the deposition rate and coating efficiency, as well as material properties were measured. Material properties investigated included: density, crush strength, micro-hardness, fracture toughness, nano-hardness, Young’s modulus, elemental composition, phase composition and microstructure. It was found that, of the variables investigated, temperature had the strongest effect while hydrogen flow rate had the least effect on material properties. There was considerable variability in all measured parameters; this introduced considerable uncertainty into the predicted effects of process conditions on material properties. / Thesis (PhD)--University of Pretoria, 2012. / Materials Science and Metallurgical Engineering / unrestricted