Thesis (M.S.)--University of Wisconsin--Madison, 1962. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 101).

Thermal spraying is a technology, which is used for coating of components and structures in order to achieve certain tribological characteristics, or for protection against corrosion, excessive temperature and wear. Within thermal spray, there are processes, which utilise combustion of liquid fuel to obtain high velocities flows providing, therefore, good adhesion of coating materials to substrates. These include High Velocity Oxygen Flame (HVOF) and High Velocity Air Flame (HVAF) process, of which the former one is widely used as it has been developed for at least two decades, while HVAF is less common. However, some studies indicate that HVAF has a number of advantages over HVOF, including the economic benefits. The thermal spray gun, based on the HVAF process, has been developed before, but the system was controlled manually. Therefore, there is a need to develop a fully automated controller of an HVAF thermal spray system. Process control of thermal spraying is highly complex as it involves simultaneous control of a number of processes, including; ignition process, combustion process, spraying material melting, as well as control and monitoring of auxiliary equipment. This paper presents the development of a control system for an HVAF thermal spray system, based on a Microchip PIC microcontroller. The designed control system was applied for controlling of thermal spraying of carbides powders, and provided a reliable ignition and stable combustion process, powder feeding and all other functions of control.

Thesis (M.S.) -- Worcester Polytechnic Institute. / Keywords: CHTE; spray quenching; flow rate; heat transfer coefficient. Includes bibliographical references (p.100-101).

Spray-forming is a newly developed industrial metal forming process in which a cylindrical metal billet is produced by the incremental deposition and solidification of an atomised metal spray on a moving substrate. A mathematical model is developed to describe billet growth and heat flow within spray-formed aluminium alloy billets. In the first part of the thesis, growth dynamics of the billet are considered. Conservation of mass at the billet surface yields a single first order quasi-linear partial differential equation for the movement of the billet surface; the nonlinearity arising from the possibility of surface shadowing. The existence of two distinctly different timescales, amongst the process motions governing billet growth, prompts the use of an averaging method. The resulting averaged equations permit analysis and are shown to provide a valid asymptotic approximation to the billet surface motion on the timescale 1/∊, for a suitably defined class of billet surfaces. The parameter ∊ ≪ 1 is the ratio of the two process timescales. Conditions under which the crown profile of the cylindrical billet becomes steady are analysed, through the averaged equations, and the stability of such profiles is examined. Computed examples of single and multiple steady state crown profiles are given. The averaged equations are also solved numerically to provide a model for transient billet growth on a "slow" timescale; results are presented. The second part of the thesis considers heat flow within the growing billet. Phase change is incorporated using an enthalpy formulation of the energy equation. The resulting equation is a nonlinear heat equation that must be solved in an expanding domain, the boundary of which is determined by solution of the billet growth model equations. Conduction on the billet length-scale takes place only on the slow timescale, with more rapid heat flow taking place only close to the billet surface. Accordingly, billet heat flow is analysed through the assumption that there is a thermal boundary layer close to the billet surface, which is driven by the "rapid" timescale spray deposition, with heat flow in the remainder of the billet driven by the time-averaged growth. The boundary layer equation is a one dimensional nonlinear advection-diffusion equation, with a nonlinear boundary condition that incorporates the intermittent deposition from the spray in the form of an irregular pulse. This equation is solved numerically using an implicit finite difference method. The slow-time heat flow is two dimensional, (assuming axisymmetric slow-time billet growth), and must also be solved numerically. For this an implicit predictor-corrector method is used. The predictor stage uses a "splitting" method, adapted from the fully implicit L.O.D. method to take account of the expanding domain. The method appears to be stable and consistent. Various numerical results are presented. The model provides significant new understanding of the dynamics of billet growth and succeeds in providing a useful framework within which the transient heat flow that occurs during spray deposition, on a number of different timescales and length-scales, can be understood. Comparison of computed model predictions with real sprayed billets confirms the validity of the model. The thesis is concluded with a summary of results and a look at possible future directions for research in this area.

Extensive research efforts are underway to generate composite coatings including carbon nanotubes (CNT) in order to improve the properties of the bulk coat. The present project concentrates on possible methods that would allow the plasma spraying of CNT-based nano-composite coatings. Various methods for producing metal-CNT composite powders for thermal plasma spraying are studied in this project. The first method discussed is based on CNT dispersion followed by an agglomeration procedure using a polymer binder. The second and more promising technique gets around the problems associated with handling, separating, and transporting the nanotubes to the substrate through a direct synthesis of the CNT on the particles to be sprayed. In the present context, this synthesis is made on pretreated stainless steel SS304 powders by chemical vapor deposition (CVD). A parametric study is made for the various steps of the thermal CVD process by varying parameters such as the etching time in the pre-treatment sequence, while the reaction temperature, the annealing temperature, the growth phase duration and the acetylene injection time are varied for the CVD sequence. The composite powders are analyzed using high resolution electron microscopy images (FEGSEM), thermogravimetric analyses (TGA), Raman spectroscopy, and BET surface area analyses. This study provided the parametric optimization of the thermal CVD procedure with respect to CNT production. The composite powders generated show a dense, fully covered, and uniform CNT forest with a purity of CNT to amorphous carbon of 86% based on the micro-Raman spectra obtained.

Thesis (doctoral)--Helsinki University of Technology, 2005. / Includes bibliographical references. Also available on the World Wide Web. Myös verkkojulkaisuna.

No description available.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfillment of the requirements for the degree of Doctor of Philosophy, Johannesburg, August 2017 / Titanium aluminides Ti3Al (α2), γ-TiAl and TiAl3 have received much attention for potential applications where light weight for energy saving, room temperature corrosion resistance in aqueous solutions, high-temperature oxidation resistance, or where combinations of the above are needed. Gamma-TiAl of composition Ti-47.5 at.% Al with additions of platinum group metals (PGMs: Pt, Pd, Ru and Ir) was investigated for microstructure, hardness, room temperature aqueous corrosion, high-temperature oxidation resistance, mechanical alloying and consolidation by spark plasma sintering, and coating on titanium Grade 2 and Ti-6Al-4V substrates. Gamma-TiAl of Ti-47.5 at.% Al produced by melting and casting gave a microstructure consisting of γ grains and lamellar grains with alternating of α2 and γ phase lamellae. Additions of 0.2, 1.0, 1.5, and 2.0 at.% PGMs introduced new phases of high PGM contents. The γ and lamellar phases were still present. The additions of PGMs significantly improved the aqueous corrosion properties at room temperature, by improving the pitting corrosion resistance of the γ-TiAl alloy by modifying its hydrogen evolution of the cathodic reaction. The presence of PGMs also influenced the oxidation behaviour of γ-TiAl at 950°by forming the Z-phase which stabilized a continuous protective Al2O3 phase. However, Ti-47.5 at.% Al, being a two-phase alloy (α2+γ), PGMs could not sustain a stable Z-phase, as it transformed into an oxygen supersaturated Ti3Al, which subsequently led to the formation of TiO2+Al2O3, a non-protective oxide mixture. The optimal PGM addition to γ-TiAl was 0.5 at.%, with iridium giving the best room temperature corrosion and high-temperature oxidation resistance. Mechanical alloying of Ti and Al pure powders with PGM additions gave powders where α2 and γ were only identified after heat treatment. Consolidation of the mechanically alloyed powders by spark plasma sintering gave different microstructures from the cast alloys, with continuous α2 and γ phases and evenly distributed nanometer-sized alumina, and much higher hardnesses. Cold spraying the mechanically alloyed powders on to titanium Grade 2 and Ti-6Al-4V substrates gave coatings of irregular thickness, dense near the substrates with porosity at the top, giving poor oxidation protection. / CK2018

An experimental investigation has been conducted on CHTE quench probes and IVF quench probes to determine the influence of flow rate, spray distance and concentration of AQ251 polymer quenchant on the cooling rate and heat transfer coefficient during spray quenching. Time-temperature data has been collected for each spraying condition using the CHTE spray quenching system. Heat transfer coefficients as a function of temperature have been estimated and compared by using lumped thermal capacity model and an inverse heat conduction model. The results revealed that the maximum cooling rate increases with increasing in the flow rate in varying concentration of polymer quenchant in both probes. It was also found that the cooling rate decreases with the increase of the concentration of polymer quenchant.

Orientador: Elson de Campos / Coorientador: Rogério Pinto Mota / Banca: Roberto Zenhei Nakazato / Banca: José Roberto Ribeiro Bortoleto / Resumo: Aços inoxidáveis martensíticos, contendo 12-13% de cromo, 2-5% de níquel e menos de 0,06% de carbono, vem sendo utilizados desde a década de 60, por exemplo, na fabricação de equipamentos hidráulicos, tais como turbinas, bombas e propulsores. Aços como o ASTM A743 CA-6NM, temperados e revenidos, passam por processos de tratamento de superfície, visando aumentar a resistência à erosão e corrosão, pois devem, operar sob condições de alta agressividade. Dentre as técnicas utilizadas para revestimento de superfície, a aspersão térmica, HVOF (Hight Velocity Oxigen Fuel), é um processo altamente utilizado, por sua viabilidade técnica e econômica. Atualmente, o aço ASTM A743 CA-6NM com revestimento do tipo WC-10Co-4Cr, com espessura em torno de 100 e 200 µm, é o material mais empregado nos diversos equipamentos hidráulicos, tais como: rotores de bombas, pás de turbinas e hélices navais. O conhecimento das características microestruturais do revestimento e de seu comportamento com relação à corrosão são de grande importância na definição dos parâmetros para a realização da aspersão térmica, gerando economia e qualidade do revestimento. Neste trabalho são realizadas análises por microscopia óptica e microscopia eletrônica de varredura com EDS sobre os revestimento aspergido com WC-10Co-4Cr, visando estudar os parâmetros relacionados à porosidade e composição da microestrutura. Além disso, foram realizadas análises da dureza, ao longo de todo o revestimento, visando estabelecer correla... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Martensitic stainless steels, containing 12-13% chromium, 2-5% nickel and less than 0.06% carbon, have been used since the 1960s, for example, in the manufacture of hydraulic equipment such as turbines, pumps and propellers. The steels ASTM A 743 CA-6NM, in quenched and tempered conditions, undergo surface treatment processes to increase resistance to erosion and corrosion, once they do operate under conditions of high aggressiveness. Among techniques used for surface coating, thermal spraying, HVOF (Hight Velocity Oxigen Fuel), is a highly utilized process, due to its technical and economical viability. Currently, ASTM A743 CA-6NM steel with WC-10Co-4Cr type coating, with a thickness of 100 µm and 200 µm, is the most used material in the various pieces of equipment, such as: pump rotors, naval blades and propellers. The knowledge of the microstructural characteristics of the coating and its behavior in relation to corrosion are of great importance, in the definition of the parameters for the realization of the thermal spray, generating economy and quality of the coating. In this paper, optical microscopy and scanning electron microscopy with EDS, on WC-10Co-4Cr sputtering coatings were carried out to study the parameters related to the porosity and microstructure composition. In addition, hardness analyses were performed throughout the coating, to establish correlation with microscopic analysis and electrochemical analysis in order to understand the behavior of the coating in saline solution NaCl 3.5% (wt/wt); all images acquired, passed by digital processing images. The results showed that the coatings obtained with 6 passes (W6) or 8 passes (W8) presented low porosity, less than 2%, and the pores measured in the W6 coating presented smaller Feret diameter and greater circularity. Dilution analysis ... (Complete abstract click electronic access below) / Mestre