No description available.

The temperature distribution in the vicinity of the laser used in direct metal deposition (DMD) plays a critical role in determining the final microstructure and properties of the deposit and the heat-affected zone within the substrate. A system of deposition samples were studied consisting of AISI 1018 steel powder deposited onto an AISI 1018 steel substrate as a single pass or as overwritten multiple passes. The laser power and speed were varied to influence the heat input and the rate of cooling. The use of idealized one dimensional lines allowed for the solution of a quasi-steady state analytical temperature distribution. Numerical predictions were made using the commercial software SysWeld™ for single pass depositions. Peak temperatures and cooling rates were determined at selected locations experimentally using micro-hardness measurements which were supplemented by obtaining thermocouple data taken during deposition. The analytical model, numerical predictions, and experimental results are compared for single pass depositions to determine the extent to which existing commercial codes can accurately model the thermal environment for DMD. / text

Laser metal deposition is an additive manufacturing technique that enables the manufacturing or repair of high-quality metal parts by building fine layers one at a time. To get a stable process with a low number of flaws and irregularities the process needs a fully operational and functioning control system. At PTC in Trollhättan, a production research facility that is a department of University West, several experiments have previously been conducted with an LMD machine.  The main objective of this thesis is to deliver input from available methods for automatic control and monitoring of the LMD process. The available methods are explained in the report and previous experiments that have been conducted have been documented in this thesis. Another objective of the thesis is to develop a prototype for monitoring and control of the process. Previous work has mainly used a visual-based control system that has used CMOS-, CCD-, or an infrared camera. Pyrometers and structured light scanning have also been used. Non-optical methods such as acoustical sensors and thermocouples have also been used for monitoring and control.  With the gathered information about the available control methods, a prototype has been developed to automatically control the LMD machine located at PTC. The control uses a CMOS camera to gather live imaging from the machine in order to adjust machine parameters, in real-time, to automatically control the process. The different parameters have a strong correlation to the final machine output and are also explained in the thesis.  The prototype and the gathering of data from the process have been made using Labview as an image-processing software. An evaluation of the developed prototype has been made and the different control methods have been discussed. The developed prototype measures the melt pool by using an algorithm that counts the number of pixels in the melt pool. However, further research needs to be made to determine if the measured width correlates with the actual width of the cladded string.

The current work focuses on three aspects of laser formed Ti-6Al-4V: an evaluation of the as-deposited and heat treated macro and microstructures and preliminary results obtained from a model developed to calculate the temperature profile resultant of the laser forming process. A "solution treat and age" heat treatment with a variable cooling rate was performed on the Laser Formed Ti-6Al-4V single line builds. Increasing the cooling rate decreases the acicular alpha grain size in the basketweave Widmanstätten alpha plus untransformed beta microstructure. Distinct features of the as-deposited macrostructure include: large columnar prior-beta grains that have grown epitaxially through multiple deposited layers; a well defined heat affected zone in the substrate; and the presence of "layer bands," a macroscopic banding present at the top of every layer except for the last three layers to be deposited. The nominal microstructure between the layer bands consists of acicular basketweave Widmanstätten alpha outlined in untransformed beta. The alpha grain width is smaller just above a layer band and larger just below a layer band. The microstructure of the layer band consists of larger colonies of acicular alpha outlined in untransformed beta. The gradient in the alpha grain size and presence of the layer band is due to thermal cycling as opposed to segregation effects which were ruled out using quantitative compositional analyses. Through analysis of the microstructural results the gradient in the nominal microstructure and formation of the layer band in layer n was caused by the deposition of layer n+2, and n+3, respectively. A thermal model has been developed to assist in the prediction and interpretation of the as-processed microstructure. The model is used to explain that the microstructural evolution of the layer bands and gradient microstructure in layer n is due to the deposition of layer n+2. The difference in the two analyses of microstructural evolution based on microstructural observations and thermal model results are due to differences in the parameter sets used to build and model the deposit. / Master of Science

The aim of this master thesis project was to statistically correlate various powder characteristics to the quality of additively manufactured parts. An additional goal of this project was to find a potential second source supplier of powder for GKN Aerospace Sweden in Trollhättan. Five Inconel® alloy 718 powders from four individual powder suppliers have been analyzed in this project regarding powder characteristics such as: morphology, porosity, size distribution, flowability and bulk properties. One powder out of the five, Powder C, is currently used in production at GKN and functions as a reference. The five powders were additively manufactured by the process of laser metal deposition according to a pre-programmed model utilized at GKN Aerospace Sweden in Trollhättan. Five plates were produced per powder and each cut to obtain three area sections to analyze, giving a total of fifteen area sections per powder. The quality of deposited parts was assessed by means of their porosity content, powder efficiency, geometry and microstructure. The final step was to statistically evaluate the results through the analysis methods of Analysis of Variance (ANOVA) and simple linear regression with the software Minitab. The method of ANOVA found a statistical significant difference between the five powders regarding their experimental results. This made it possible to compare the five powders against each other. Statistical correlations by simple linear regression analysis were found between various powder characteristics and quality of deposited part. This led to the conclusion that GKN should consider additions to current powder material specification by powder characteristics such as: particle morphology, powder porosity and flowability measurements by a rheometer. One powder was found to have the potential of becoming a second source supplier to GKN, namely Powder A. Powder A had overall good powder properties such as smooth and spherical particles, high particle density at 99,94% and good flowability. The deposited parts with Powder A also showed the lowest amount of pores compared to Powder C, a total of 78 in all five plates, and sufficient powder efficiency at 81,6%.

Esta Tese descreve a preparação de novos eletrodos modificados (EMs) fazendo uso de um método novo, a deposição de partículas de metais nobres, como níquel, paládio e platina sobre partículas de metais comuns, como cobre e ferro. Este método leva aos denominados EMs mistos, que podem apresentar características diferentes e mais eficientes que os EMs Ni, Pd e Pt já estudados, sendo a principal aplicação nas reações de hidrogenação eletrocatalítica (HEC) de substratos orgânicos insaturados. A preparação dos EMs mistos se inicia pelo recobrimento da superfície do eletrodo de trabalho com um filme polimérico. O polímero usado foi o poli-(éter alílico do ácido p-benzenossulfônico), um filme aniônico com boa estabilidade química e mecânica, que pode fazer troca iônica de seus íons H+ por cátions metálicos. Este filme é preparado por varreduras de voltametria cíclica de uma solução do respectivo monômero, que se oxida eletroquimicamente iniciando a reação química de polimerização. Os metais cobre e ferro são introduzidos ao polímero pelo método de troca iônica/redução eletroquímica, onde o EM é mergulhado em uma solução saturada de um sal de cobre ou de ferro para ocorrer a troca iônica. Em seguida, estes íons são reduzidos eletroquimicamente por varreduras de voltametria cíclica, usando uma faixa de potencial adequada. Para se preparar os EMs mistos, mergulhou-se estes EMs (Cu ou Fe) na solução do banho electroless de níquel, paládio e platina. Por esta metodologia partículas destes metais nobres são depositadas pelo processo de deposição metálica electroless (DME), que faz uso de um agente redutor, hipofosfito de sódio, para reduzir os íons destes metais de forma adequada nos EMs Cu ou Fe e onde se espera obter grande área superficial. Os EMs mistos preparados foram: Cu/Ni, Cu/Pd, Cu/Pt, Fe/Ni, Fe/Pd e Fe/Pt. A caracterização dos metais dos EMs mistos foi feita indiretamente por geração eletroquímica de hidrogênio (GH) de uma solução ácida e diretamente pelas técnicas de Difração de Raios X e Microscopia de Varredura Eletrônica (MEV). O processo de deposição metálica foi investigado por medidas de potencial de circuito aberto, realizadas durante a deposição dos metais nobres que indicou a ocorrência do processo de DME em alguns casos e DG (deposição galvânica) em outros. Devido a alguns resultados do processo de deposição metálica, foi estudado o mecanismo de catalise na deposição direta das partículas de níquel, paládio e platina pela redução química por hipofosfito dos íons correspondentes. Preparou-se EMs Ni, Pd e Pt por dois métodos: troca iônica/redução eletroquímica e troca iônica/redução química catalisada pelo filme. Estes foram caracterizados por GH e utilizando o ácido p-toluenossulfônico como modelo, estudos de espectroscopia na região UV/Vis. foram realizados. Estas medidas comprovaram a catálise, pois os EMs preparados por redução química apresentaram melhores resultados para a GH e as análises de UV/Vis. mostraram a forte ligação existente entre os grupos sulfonatos do polímero e os íons metálicos bivalentes, ligação essencial para ocorrer a catálise do filme. Verificou-se que as partículas dos metais nobres podiam estar sendo depositadas por DME ou por DG seguido de DME, mas que em todos os casos ocorria a deposição causada pela catálise do filme. A reatividade dos EMs mistos foi avaliada por um estudo cinético, onde HECs de alguns substratos orgânicos foram realizadas e acompanhadas por medidas de UV/Vis. durante as reações. Obteve-se a constante de velocidade (k) destas reações, as quais foram comparadas entre si e encontrou-se como o EM misto mais eficiente o Cu/Pt. As ks das reações deste EM foram comparadas com ks de outros EMs de Pt, já estudados em nossos laboratórios. / This thesis describes the preparation of new modified electrodes (MEs) using the method of noble metal particles deposition like nickel, palladium and platinum in the surface of commum metals particles as cooper and iron. This new electrodes were denominated mixed MEs, and can show different caractheristics and present higher efficiency than others already studied, being their principal application in electrocatalytic hydrogenation (ECH) of unsaturated organic substrates. The surface electrode were coated with the polymer poly-(ether allyl p-benzenesulfonic), an anionic film with good chemical and mechanic stability that can undergoes ion exchange of ions H+ by metallic cations. This film is prepared by anodic oxidation of the monomer using voltammetric cycles, producing a cation radical initiador of a chain reaction polymerization. Cooper and iron metals are incorporated in the polymer by ion exchange/ electrochemical reduction; the ME were dipped in saturated solution of cooper or iron salt to produce the ion exchange. The ions are then electrochemically reduced. The preparation of mixed MEs is carried out by electrolessly deposidated Ni, Pd or Pt. This methodology use NaH2PO2, to reduce the metal ions. This procedure deposits Ni, Pd and Pt in the surface of Cu or Fe MEs with an expected higher superficial area. The mixed Cu/Ni, Cu/Pd, Cu/Pt, Fe/Ni, Fe/Pd e Fe/Pt MEs were prepared. The characterization of the MEs metals was made indirectly by electrochemically hydrogen generation from an acid solution (HG) and directly by SEM-EDX and Ray X Diffraction analysis. The metallic deposition process was investigated by open circuit during the deposition of nobles metals that indicate the occurrence of electroless deposition (EMD) process in some cases or spontaneous displacement reaction (galvanic deposition - GD) in others. Despite the two mechanisms related above, a catalytic process would occur. To rut in evidence this third process Ni, Pd and Pt MEs were prepared by two methods: ion exchange/electrochemical reduction and ion exchange/chemical reduction catalyzed by the film. The resulting MEs were characterized by HG and spectroscopy in the UV/Vis. For this last analysis, p-toluenossulfonic acid was used as model and the results proved the catalytic mechanism. UV spectroscopy analysis showed strong bonds between the p-toluenossulfonic and the noble metal salts. So particles of noble metals can be deposited not only by EMD or GD but in all cases occur the deposition by film catalysis too. The reactivity of mixed MEs was done by kinetic study, where ECH of some organic substrates were carried out and monitored by UV/Vis spectroscopy. The constant rate (k) of the reactions was calculated and compared with the others mixed MEs. The ks of this ME were compared with the ks of other Pt MEs, already studied. The more reactive of them was the Cu/Pt ME.

Metal deposition is an additive layered manufacturing process that deposits molten metal droplets on a substrate and by repeating this process layer by layer, a complex shaped 3D geometry can be manufactured. In this thesis, the metal deposition process is performed by a robot with a wire feeder tool and a laser as energy source to melt the metal wire. The robot programming for robotized metal deposition process can be completely automated by computer aided robotics software. University West is currently developing an add-in application in a computer aided robotics software, Process Simulate, that is capable of programming the robotized metal deposition process. The first goal of this thesis was to verify the up to now developed software and the process from CAD drawing down to robot code. Another goal was to find and implement an algorithm that will reduce the number of locations on a circular arc to three locations. The algorithm to minimize the locations must be capable of changing all the different curvature paths to linear and circular arc motions which are easy to translate to robot code. The user should be able to decide the fitting precision of the approximated motion path to the original path. A real robot cell setup is modelled in Process Simulate. This lets Process Simulate generate the correct robot code for that specific cell.  Since each robot cell has its own unique setup, a custom script will be developed that changes the universal robot code, that Process Simulate generates, to the custom robot code required in this specific robot cell. The software is improved and tested from CAD drawing down to robot code but still needs to be debugged more and needs implementation of some non-existing features.

Nowadays, the development of novel materials involves diverse branches of science as a consequence of the new requirements imposed by modern society. This includes aspects ranging from the optimization of the manufacturing processes to the durability of the materials themselves. Ideally, some synergism should exist between the durability, the properties of interest in the material. Although metals in their pure state are often desired, the best properties or combination of properties often cannot be satisfactorily achieved with a single metal. In these situations, the desired properties can be attained by the formation of alloys of these metals with others. Ni-Co alloys are no exceptions and so have received considerable attention especially in microsystem technology due to the magnetic properties of cobalt and the corrosion and wear resistance of nickel. Moreover, this interest has been further stimulated by its use in the manufacture of sensors, magnetic devices, microrelays, inductors, actuators, memory devices and hard drives. The fabrication of these alloys (particularly coatings) via electroplating has been shown to be techno-economically feasible in comparison with other processes: capability of high volume production, low cost and the ability to coat thin layers on non-planar substrates. In addition, the materials fabricated by this technology exhibit excellent characteristics such as refined grain structure, smoothness, low residual stress and coercivity, etc., making them advantageous to materials produced by other physical methods of deposition. Nevertheless, one of the biggest problems faced during the formation of Ni-Co alloys is its anomalous behavior whereby cobalt preferentially deposits over nickel under most conditions, even when the Ni(II) concentration is significantly higher than that of Co(II). This problem has complicated the prediction and control of the metal composition in these alloys during their production and as a consequence the ability to obtain the desirable properties associated with high nickel content. Although this problem is not recent, the studies that have been carried out so far to analyze this system have not always been as comprehensive as they could be in terms of the experimental conditions investigated or the reaction mechanisms and mathematical models developed to describe its behavior. Consequently, the origin of this behavior is still not completely understood. Thus, this work presents a contribution in terms of the analysis of the reaction mechanisms for single metal deposition of nickel and cobalt and for the formation of Ni-Co alloys in sulphate media with the intention of gaining a better understanding of the phenomena controlling the anomalous behavior of this system. Analyses of the single metal deposition of nickel and cobalt are first carried out to better understand their reaction mechanisms. Such an approach should allow the contributions of the reduction of each metal ion and interactions between the two systems during alloy co-deposition to be more clearly understood. In order to analyse the aforementioned systems, both steady state and transient techniques are employed. Among these techniques, electrochemical impedance spectroscopy (EIS) is employed since it is a robust and powerful method to quantitatively characterize the various relaxation phenomena occurring during the electrodeposition of metals. The experimental data acquired from this technique are analyzed with comprehensive physicochemical models and the electrochemical processes are quantified by fitting the models to these data to determine the kinetic parameters. During the development of the physicochemical models, several assumptions (e.g. neglect of convection, homogeneous reactions and single electron-transfer steps) made in former models are relaxed in order to investigate their combined impact on the predicted response of the system. Estimates of the kinetic parameters determined by EIS for the deposition of the single metals reveals that the first step of Co(II) reduction is much faaster tha the corresponding step of Ni(II) reduction. Some limitations of the EIS technique (i.e. analysis at high overpotentials) are exposed and compared in the case of the nickel deposition using linear sweep voltammetry (LSV). Likewise, physicochemical models accounting for most of the important phenomena are derived and fitted to experimental data. Ni-Co alloy formation is analyzed using LSV and steady state polarization experiments for different pH, current density and electrolyte composition. Current efficiencies for metal depsoition and alloy composition are also evaluated. To date, no experimental study considering all these variables has been reported in the literature. Then a steady state model is presented to describe the electrode response during alloy formation and used to provide insight into the anomalous behavior of this system. This model is based on information obtained from previous studies reported in the literature and from the current research. After being fitted to the experimental data, the model reveals that the anomalous behavior observed for this alloy is likely caused by the much faster charge-transfer of Co(II) reduction than that of Ni(II) reduction and not by other previously proposed mechanisms such as competition between adsorbed species for surface sites, formation of aqueous hydroxides (MeOH+) or mixed intermediate species (NiCo(III)ads) on the surface of the electrode.

No description available.

Nowadays, the development of novel materials involves diverse branches of science as a consequence of the new requirements imposed by modern society. This includes aspects ranging from the optimization of the manufacturing processes to the durability of the materials themselves. Ideally, some synergism should exist between the durability, the properties of interest in the material. Although metals in their pure state are often desired, the best properties or combination of properties often cannot be satisfactorily achieved with a single metal. In these situations, the desired properties can be attained by the formation of alloys of these metals with others. Ni-Co alloys are no exceptions and so have received considerable attention especially in microsystem technology due to the magnetic properties of cobalt and the corrosion and wear resistance of nickel. Moreover, this interest has been further stimulated by its use in the manufacture of sensors, magnetic devices, microrelays, inductors, actuators, memory devices and hard drives. The fabrication of these alloys (particularly coatings) via electroplating has been shown to be techno-economically feasible in comparison with other processes: capability of high volume production, low cost and the ability to coat thin layers on non-planar substrates. In addition, the materials fabricated by this technology exhibit excellent characteristics such as refined grain structure, smoothness, low residual stress and coercivity, etc., making them advantageous to materials produced by other physical methods of deposition. Nevertheless, one of the biggest problems faced during the formation of Ni-Co alloys is its anomalous behavior whereby cobalt preferentially deposits over nickel under most conditions, even when the Ni(II) concentration is significantly higher than that of Co(II). This problem has complicated the prediction and control of the metal composition in these alloys during their production and as a consequence the ability to obtain the desirable properties associated with high nickel content. Although this problem is not recent, the studies that have been carried out so far to analyze this system have not always been as comprehensive as they could be in terms of the experimental conditions investigated or the reaction mechanisms and mathematical models developed to describe its behavior. Consequently, the origin of this behavior is still not completely understood. Thus, this work presents a contribution in terms of the analysis of the reaction mechanisms for single metal deposition of nickel and cobalt and for the formation of Ni-Co alloys in sulphate media with the intention of gaining a better understanding of the phenomena controlling the anomalous behavior of this system. Analyses of the single metal deposition of nickel and cobalt are first carried out to better understand their reaction mechanisms. Such an approach should allow the contributions of the reduction of each metal ion and interactions between the two systems during alloy co-deposition to be more clearly understood. In order to analyse the aforementioned systems, both steady state and transient techniques are employed. Among these techniques, electrochemical impedance spectroscopy (EIS) is employed since it is a robust and powerful method to quantitatively characterize the various relaxation phenomena occurring during the electrodeposition of metals. The experimental data acquired from this technique are analyzed with comprehensive physicochemical models and the electrochemical processes are quantified by fitting the models to these data to determine the kinetic parameters. During the development of the physicochemical models, several assumptions (e.g. neglect of convection, homogeneous reactions and single electron-transfer steps) made in former models are relaxed in order to investigate their combined impact on the predicted response of the system. Estimates of the kinetic parameters determined by EIS for the deposition of the single metals reveals that the first step of Co(II) reduction is much faaster tha the corresponding step of Ni(II) reduction. Some limitations of the EIS technique (i.e. analysis at high overpotentials) are exposed and compared in the case of the nickel deposition using linear sweep voltammetry (LSV). Likewise, physicochemical models accounting for most of the important phenomena are derived and fitted to experimental data. Ni-Co alloy formation is analyzed using LSV and steady state polarization experiments for different pH, current density and electrolyte composition. Current efficiencies for metal depsoition and alloy composition are also evaluated. To date, no experimental study considering all these variables has been reported in the literature. Then a steady state model is presented to describe the electrode response during alloy formation and used to provide insight into the anomalous behavior of this system. This model is based on information obtained from previous studies reported in the literature and from the current research. After being fitted to the experimental data, the model reveals that the anomalous behavior observed for this alloy is likely caused by the much faster charge-transfer of Co(II) reduction than that of Ni(II) reduction and not by other previously proposed mechanisms such as competition between adsorbed species for surface sites, formation of aqueous hydroxides (MeOH+) or mixed intermediate species (NiCo(III)ads) on the surface of the electrode.