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Laser cladding is a process that is used to improve the properties of a metal surface. The properties in question may include hardness, wear-, corrosion- and/or fatigue-resistance. The process involves fusing a thin layer of additional metal to the original surface, using a laser as the heat source. Unfortunately, residual stresses are generated due to the rapid and highly localised thermal expansion and contraction that occur during the heating-melting-solidification-cooling cycle. These residual stresses can have a detrimental effect on the final performance of the clad component, especially with respect to corrosion resistance. Detrimental tensile residual stresses can be mitigated through the use of post-processing techniques such as laser shock peening (LSP). LSP is a process that uses a pulsed laser to generate intense spots of recoil pressure on a surface, thereby introducing compressive residual stresses. Post weld heat treatment (PWHT) is another process that could be also used in laser cladding in order to relieve tensile residual stresses. In this work, laser cladding was carried out by depositing a clad layer of AISI grade 316L stainless steel on to either a S275 steel substrate or an AISI grade 316L stainless steel substrate, using different process parameters. The hardness and residual stresses in the overlay and substrate were assessed for each laser clad sample before and after being treated with LSP and PWHT. The corrosion rate and microstructure were also assessed in each case. The novelty of this work is two-fold. Firstly, to the author's knowledge, it is the first study that attempts to link process parameters to both the residual stresses and the corrosion performance of austenitic stainless steel overlays deposited by laser cladding. The second novel aspect is based on the application of both LSP and PWHT to the deposited overlay in order to investigate whether an improvement in the mechanical properties and the corrosion resistance can be realised. In this study, tensile residual stresses were generated in the clad layers. However, the magnitude of the residual stresses did not appear to be particularly sensitive to the deposition parameters. Indeed, it was found that the number of layers that is deposited is more important than the choice of process parameters. LSP was effective in reducing the tensile residual stresses and in fact it introduced compressive stresses to all the samples that were treated. In contrast, PWHT only led to satisfactory stress relief when the AISI grade 316L stainless steel was deposited on to a matching substrate material. This was related to the fact that a difference between the thermal expansion coefficients of the overlay and substrate led to the development of significant tensile residual stresses on cooling down after PWHT. The corrosion tests on the clad coupons led to the development of pits and cracks. However, after LSP only pits were found, without any sign of cracking, for the test durations that were investigated owing to the fact that compressive stresses were generated. Similar results were found after PWHT for the clad samples in which the overlay material matched the substrate material. However, signs of cracking were observed after PWHT in samples where AISI grade 316L stainless steel was deposited on to an S275 steel substrate due to tensile residual stresses remaining within the overlay. This result suggests that there may be little benefit in carrying out PWHT for components in which grade 316L stainless steel is deposited on to a steel substrate. In contrast, there appear to be clear benefits associated with carrying out LSP in order to mitigate the residual stresses and retard the onset of cracking.

In laser cladding, a material, usually in the form of powder, is deposited on a substrate. Powder particles are intermingled with inert gas and fed by a powder feeder system on the substrate. Laser is employed to melt the additive material and a small layer of surface of the substrate simultaneously. While the powder is being deposited, the laser melts the powder particles and the melted powder particles join the melt pool on the substrate beneath the laser beam. Generating relative motion between the laser focal point and the substrate will result in moving melt pool on the substrate. This will lead to addition of a desired material to the substrate with desired thickness and good bonding as well as minimum dilution. In addition, by producing clads beside and on the top of each other a functional component can be built in a layer by layer fashion. Despite many advantages of laser cladding, it is highly sensitive to internal and external disturbances. This makes a closed-loop control system for laser cladding inevitable. Utilizing a closed-loop control system in laser cladding makes the system insensitive to external and internal disturbances. Having a closed-loop control system for laser cladding would contribute to substantial improvement in clad quality and cost reduction. Feedback sensor is an essential part in a closed-loop control system. Among different parameters that can be used as feedback signals in a closed-loop control of laser cladding, melt pool geometry and in particular clad height is of great importance specifically for the purpose of rapid prototyping. This thesis presents novel algorithms for real-time detection of clad height in laser cladding. This is accomplished by the following: Tackling the issues pertinent to image acquisition in the presence of harsh and intensive light is scrutinized. Important parameters of digital cameras related to selection of proper type of CCD cameras in order to overcome the existent harsh condition are presented. Also, the existent light in laser cladding arisen from different sources is analyzed and based upon that proper bandpass filters and neutral filters are selected. All these lead to capture relatively sharp and clear images of the melt pool. Capturing good quality pictures potentially would provide valuable information about the process. This information could include, but is not limited to, melt pool geometry (i.e., melt pool height, width, melt pool profile, and wet angle), angle of solidification, melt pool temperature, and melt pool temperature distribution. Furthermore, the issues regarding path dependency of the melt pool image are addressed by using a trinocular cameras configuration. By utilizing this, always two cameras monitor the front end of the melt pool regardless of the direction of the clad. Image analysis of the grabbed images is also discussed. Image thresholding is one of the most formidable tasks in image processing and this difficulty is intensified due to characteristics of the grabbed images of the melt pool (e.g., surrounding hazy area around the melt pool). Applying hard partitioning thresholding method did not lead to detec- tion of the melt pool accurately. As a result, fuzzy thresholding by minimizing of the measure of fuzziness is developed and its performance is investigated. The effect of three important membership functions, triangular, Gaussian, and generalized Bell on the performance of the thresholding method is investigated. Also, Image thresholding by utilizing fuzzy c-means clustering is developed. Applying the developed thresholding methods show promising results. Among the developed thresholding methods, fuzzy thresholding with minimizing the measure of fuzziness with Gaussian membership function is selected for the implementation in the algorithm. Finally, Image feature tracking module is presented. The detected borders of the melt pool images are transformed from image plane to the world plane by using a perspective transformation. Four features of the elliptical features of the projected melt pool borders are selected. These four features along with the angle of tangential path vector with respect to the corresponding right hand side camera's axis are fed into an Elman recurrent neural network. The proposed algorithms and the trained neural network are utilized in the process resulting in acceptable detection of the clad height in deposition of straight clads for a specific direction. It is concluded that the system can detect the clad height with about ±0.15 mm maximum error.

In laser cladding, a material, usually in the form of powder, is deposited on a substrate. Powder particles are intermingled with inert gas and fed by a powder feeder system on the substrate. Laser is employed to melt the additive material and a small layer of surface of the substrate simultaneously. While the powder is being deposited, the laser melts the powder particles and the melted powder particles join the melt pool on the substrate beneath the laser beam. Generating relative motion between the laser focal point and the substrate will result in moving melt pool on the substrate. This will lead to addition of a desired material to the substrate with desired thickness and good bonding as well as minimum dilution. In addition, by producing clads beside and on the top of each other a functional component can be built in a layer by layer fashion. Despite many advantages of laser cladding, it is highly sensitive to internal and external disturbances. This makes a closed-loop control system for laser cladding inevitable. Utilizing a closed-loop control system in laser cladding makes the system insensitive to external and internal disturbances. Having a closed-loop control system for laser cladding would contribute to substantial improvement in clad quality and cost reduction. Feedback sensor is an essential part in a closed-loop control system. Among different parameters that can be used as feedback signals in a closed-loop control of laser cladding, melt pool geometry and in particular clad height is of great importance specifically for the purpose of rapid prototyping. This thesis presents novel algorithms for real-time detection of clad height in laser cladding. This is accomplished by the following: Tackling the issues pertinent to image acquisition in the presence of harsh and intensive light is scrutinized. Important parameters of digital cameras related to selection of proper type of CCD cameras in order to overcome the existent harsh condition are presented. Also, the existent light in laser cladding arisen from different sources is analyzed and based upon that proper bandpass filters and neutral filters are selected. All these lead to capture relatively sharp and clear images of the melt pool. Capturing good quality pictures potentially would provide valuable information about the process. This information could include, but is not limited to, melt pool geometry (i.e., melt pool height, width, melt pool profile, and wet angle), angle of solidification, melt pool temperature, and melt pool temperature distribution. Furthermore, the issues regarding path dependency of the melt pool image are addressed by using a trinocular cameras configuration. By utilizing this, always two cameras monitor the front end of the melt pool regardless of the direction of the clad. Image analysis of the grabbed images is also discussed. Image thresholding is one of the most formidable tasks in image processing and this difficulty is intensified due to characteristics of the grabbed images of the melt pool (e.g., surrounding hazy area around the melt pool). Applying hard partitioning thresholding method did not lead to detec- tion of the melt pool accurately. As a result, fuzzy thresholding by minimizing of the measure of fuzziness is developed and its performance is investigated. The effect of three important membership functions, triangular, Gaussian, and generalized Bell on the performance of the thresholding method is investigated. Also, Image thresholding by utilizing fuzzy c-means clustering is developed. Applying the developed thresholding methods show promising results. Among the developed thresholding methods, fuzzy thresholding with minimizing the measure of fuzziness with Gaussian membership function is selected for the implementation in the algorithm. Finally, Image feature tracking module is presented. The detected borders of the melt pool images are transformed from image plane to the world plane by using a perspective transformation. Four features of the elliptical features of the projected melt pool borders are selected. These four features along with the angle of tangential path vector with respect to the corresponding right hand side camera's axis are fed into an Elman recurrent neural network. The proposed algorithms and the trained neural network are utilized in the process resulting in acceptable detection of the clad height in deposition of straight clads for a specific direction. It is concluded that the system can detect the clad height with about ±0.15 mm maximum error.

O objetivo do presente trabalho é avaliar a microestrutura e as propriedades da superliga MAR-M247 modificada com nióbio (composição nominal: 10,2% em peso Co; 10,2W; 8,5Cr; 5,6Al; 1,6Nb; 1,4Hf; 1,1Ti; 0,7Mo; 0,15C; 0,06Zr; 0,015B; Ni balanço) submetida a diferentes rotas de processamento (tratamento térmico, laser cladding e oxidação isotérmica). O material foi produzido por fusão por indução a vácuo na empresa Açotécnica S.A. (Jandira/SP). As amostras no estado bruto de fusão e tratadas termicamente (solubilização e envelhecimento em uma e duas etapas por diferentes temperaturas e tempos) foram analisadas por MEV e MEV-FEG com EDS. Também foram realizadas medidas de análise térmica diferencial (DTA), dureza, difração de raios X e simulações em Thermo-Calc, JMatPro e PandaT. Em outra parte desta tese, realizada no Instituto Superior Técnico em Lisboa/Portugal, as amostras da superliga MAR-M247(Nb) foram fundidas pela técnica de laser melting e caracterizadas por MEV-FEG, EDS, dureza e EBSD, além de diversos cálculos envolvendo os parâmetros de processo utilizados. Além disso, os experimentos de deposição de pós de NiCr, NiCrAl e NiCrAlY no substrato da superliga MAR-M247(Nb) utilizando a técnica de laser cladding permitiram calcular alguns parâmetros geométricos e analisar a microestrutura dos depósitos (MEV-FEG, EDS e medidas de dureza) após o processamento e os tratamentos térmicos. Na última parte desta tese, foram realizados ensaios de oxidação isotérmica a 1000°C por até 216 horas (ar estático) na superliga MAR-M247(Nb). As amostras oxidadas (superfície e seção transversal) foram analisadas por MEV, medidas por EDS (pontual, line scan e mapeamento) e difração de raios X, além de cálculos das constantes kp e n. Os resultados desta tese permitem comparar as temperturas solvus de ?\' (1210oC), solidus (1310oC) e liquidus (1360oC) obtidas por Thermo-Calc com as temperaturas solvus de ?\' (1238oC), de fusão incipiente (1281oC) e liquidus (1370oC) obtidas por experimentos de análise térmica diferencial para a superliga MAR-M247(Nb). A microestrutura da superliga MARM247(Nb) no estado bruto de fusão é dendrítica com carbetos de W, Ti, Nb e Hf nas regiões interdendríticas. O tratamento de solubilização a 1260°C por 8 horas foi escolhido como condição ideal, enquanto que o tratamento de envelhecimento a 980°C por 80 horas apresentou o maior tamanho de partícula de ?\'. O material fundido pela técnica de laser melting apresentou trincas devido à formação de regiões eutéticas ?/?\' de baixo ponto de fusão. A microestrutura dos depósitos de NiCr, NiCrAl e NiCrAlY as clad é dendrítica com a fase solução sólida ?-Ni(Cr), além de poros e óxidos/carbetos. O depósito de NiCrAlY possui fases ricas em ítrio. A amostra de NiCr tratada 1150oC por 50 horas não apresentou evidências de segregação enquanto que as amostras de NiCrAl e NiCrAlY apresentaram a fase ?\' precipitada fina e uniformemente após tratamento térmico a 1100 e 1150°C por 10 e 50 horas. A estrutura da camada óxida da superliga MAR-M247(Nb) submetida a ensaios de oxidação isotérmica a 1000°C por até 216 horas consiste de NiO na camada externa, Cr2O3, TiO2, CoO, espinélios de (Ni,Co)Cr2O4 e partículas de W20O58 e HfO2 na camada intermediária e Al2O3 na camada interna. Finalmente, conclui-se que a microestrutura e as propriedades da superliga MAR-M247(Nb) são alteradas quando as rotas de processamento (tratamento térmico, laser cladding e oxidação isotérmica) mudam. / The aim of this work is to evaluate the microstructure and the properties of the niobiummodified MAR-M247 superalloy (nominal composition: 10.2 weight percent of Co; 10.2W; 8.5Cr; 5.6Al; 1.6Nb; 1.4Hf; 1.1Ti; 0.7Mo; 0.15C; 0.06Zr; 0.015B; Ni balance) submitted to different processing routes (heat-treatment, laser cladding and isothermal oxidation). The material was produced by vacuum induction melting at Açotécnica Company (Jandira/SP). The as-cast and heat-treated samples (solution and aging in one and two steps at different temperatures and times) were analyzed in SEM and FEG-SEM with EDX. Differential thermal analysis (DTA), hardness, X-ray diffraction and simulations with Thermo-Calc, JMatPro and PandaT were performed as well. In another part of this thesis, performed at Instituto Superior Técnico in Lisbon/Portugal, the samples of the MAR-M247(Nb) superalloy were produced by laser melting technique and characterized by FEG-SEM, EDX, hardness, and EBSD, besides some calculations involving the process parameters utilized. Furthermore, the experiments of NiCr, NiCrAl and NiCrAlY powder deposition on the substrate of MAR-M247(Nb) superalloy utilizing the laser cladding technique allowed the calculation of some geometric parameters, as well as the analysis of the microstructure of the deposits (FEG-SEM, EDX and hardness) after the processing and the heat-treatments. In the last part of this work, experiments of isothermal oxidation at 1000°C for up to 216 hours (static air) were performed in the MAR-M247(Nb) superalloy. The oxidized samples (surface and cross-section) were analyzed by SEM, EDX (punctual, line scan and mapping) and X-ray diffraction, besides some calculations of kp and n constants. The results of this thesis allow comparing the ?\' solvus (1210oC), solidus (1310oC) and liquidus (1360oC) temperatures obtained by Thermo-Calc with the ?\' solvus (1238oC), incipient melting (1281oC) and liquidus (1370oC) temperatures obtained by differential thermal analysis experiments of the MARM247(Nb) superalloy. The microstructure of the as-cast MAR-M247(Nb) superalloy is dendritic with W, Ti, Nb and Hf carbides in the interdendritic regions. The solution heattreatment at 1260°C for 8 hours was chosen as the ideal condition, whilst the aging heattreatment at 980°C for 80 hours presented the highest ?\' particle size. The material processed by laser melting technique showed cracks due to formation of low melting point ?/?\' eutectic regions. The microstructure of the NiCr, NiCrAl and NiCrAlY as clad deposits is dendritic with the ?-Ni(Cr) solid solution phase, besides pores and oxides/carbides. The NiCrAlY deposit has yttrium-rich phases. The NiCr sample heattreated at 1150oC for 50 hours didn\'t present evidences of segregation whilst the NiCrAl and NiCrAlY samples presented fine and uniform ?\' phase precipitated after the heattreatment at 1100 and 1150°C for 10 and 50 hours. The structure of the oxide layer of the MAR-M247(Nb) superalloy submitted to isothermal oxidation experiments at 1000°C for up to 216 hours has NiO in the outer layer, Cr2O3, TiO2, CoO, (Ni,Co)Cr2O4 spinels and W20O58 and HfO2 particles in the intermediate layer, and Al2O3 in the inner layer. Finally, it is possible to conclude that the microstructure and the properties of the MAR-M247(Nb) superalloy are modified when the processing routes (heat-treatment, laser cladding and isothermal oxidation) are changed.

O objetivo do presente trabalho é avaliar a microestrutura e as propriedades da superliga MAR-M247 modificada com nióbio (composição nominal: 10,2% em peso Co; 10,2W; 8,5Cr; 5,6Al; 1,6Nb; 1,4Hf; 1,1Ti; 0,7Mo; 0,15C; 0,06Zr; 0,015B; Ni balanço) submetida a diferentes rotas de processamento (tratamento térmico, laser cladding e oxidação isotérmica). O material foi produzido por fusão por indução a vácuo na empresa Açotécnica S.A. (Jandira/SP). As amostras no estado bruto de fusão e tratadas termicamente (solubilização e envelhecimento em uma e duas etapas por diferentes temperaturas e tempos) foram analisadas por MEV e MEV-FEG com EDS. Também foram realizadas medidas de análise térmica diferencial (DTA), dureza, difração de raios X e simulações em Thermo-Calc, JMatPro e PandaT. Em outra parte desta tese, realizada no Instituto Superior Técnico em Lisboa/Portugal, as amostras da superliga MAR-M247(Nb) foram fundidas pela técnica de laser melting e caracterizadas por MEV-FEG, EDS, dureza e EBSD, além de diversos cálculos envolvendo os parâmetros de processo utilizados. Além disso, os experimentos de deposição de pós de NiCr, NiCrAl e NiCrAlY no substrato da superliga MAR-M247(Nb) utilizando a técnica de laser cladding permitiram calcular alguns parâmetros geométricos e analisar a microestrutura dos depósitos (MEV-FEG, EDS e medidas de dureza) após o processamento e os tratamentos térmicos. Na última parte desta tese, foram realizados ensaios de oxidação isotérmica a 1000°C por até 216 horas (ar estático) na superliga MAR-M247(Nb). As amostras oxidadas (superfície e seção transversal) foram analisadas por MEV, medidas por EDS (pontual, line scan e mapeamento) e difração de raios X, além de cálculos das constantes kp e n. Os resultados desta tese permitem comparar as temperturas solvus de ?\' (1210oC), solidus (1310oC) e liquidus (1360oC) obtidas por Thermo-Calc com as temperaturas solvus de ?\' (1238oC), de fusão incipiente (1281oC) e liquidus (1370oC) obtidas por experimentos de análise térmica diferencial para a superliga MAR-M247(Nb). A microestrutura da superliga MARM247(Nb) no estado bruto de fusão é dendrítica com carbetos de W, Ti, Nb e Hf nas regiões interdendríticas. O tratamento de solubilização a 1260°C por 8 horas foi escolhido como condição ideal, enquanto que o tratamento de envelhecimento a 980°C por 80 horas apresentou o maior tamanho de partícula de ?\'. O material fundido pela técnica de laser melting apresentou trincas devido à formação de regiões eutéticas ?/?\' de baixo ponto de fusão. A microestrutura dos depósitos de NiCr, NiCrAl e NiCrAlY as clad é dendrítica com a fase solução sólida ?-Ni(Cr), além de poros e óxidos/carbetos. O depósito de NiCrAlY possui fases ricas em ítrio. A amostra de NiCr tratada 1150oC por 50 horas não apresentou evidências de segregação enquanto que as amostras de NiCrAl e NiCrAlY apresentaram a fase ?\' precipitada fina e uniformemente após tratamento térmico a 1100 e 1150°C por 10 e 50 horas. A estrutura da camada óxida da superliga MAR-M247(Nb) submetida a ensaios de oxidação isotérmica a 1000°C por até 216 horas consiste de NiO na camada externa, Cr2O3, TiO2, CoO, espinélios de (Ni,Co)Cr2O4 e partículas de W20O58 e HfO2 na camada intermediária e Al2O3 na camada interna. Finalmente, conclui-se que a microestrutura e as propriedades da superliga MAR-M247(Nb) são alteradas quando as rotas de processamento (tratamento térmico, laser cladding e oxidação isotérmica) mudam. / The aim of this work is to evaluate the microstructure and the properties of the niobiummodified MAR-M247 superalloy (nominal composition: 10.2 weight percent of Co; 10.2W; 8.5Cr; 5.6Al; 1.6Nb; 1.4Hf; 1.1Ti; 0.7Mo; 0.15C; 0.06Zr; 0.015B; Ni balance) submitted to different processing routes (heat-treatment, laser cladding and isothermal oxidation). The material was produced by vacuum induction melting at Açotécnica Company (Jandira/SP). The as-cast and heat-treated samples (solution and aging in one and two steps at different temperatures and times) were analyzed in SEM and FEG-SEM with EDX. Differential thermal analysis (DTA), hardness, X-ray diffraction and simulations with Thermo-Calc, JMatPro and PandaT were performed as well. In another part of this thesis, performed at Instituto Superior Técnico in Lisbon/Portugal, the samples of the MAR-M247(Nb) superalloy were produced by laser melting technique and characterized by FEG-SEM, EDX, hardness, and EBSD, besides some calculations involving the process parameters utilized. Furthermore, the experiments of NiCr, NiCrAl and NiCrAlY powder deposition on the substrate of MAR-M247(Nb) superalloy utilizing the laser cladding technique allowed the calculation of some geometric parameters, as well as the analysis of the microstructure of the deposits (FEG-SEM, EDX and hardness) after the processing and the heat-treatments. In the last part of this work, experiments of isothermal oxidation at 1000°C for up to 216 hours (static air) were performed in the MAR-M247(Nb) superalloy. The oxidized samples (surface and cross-section) were analyzed by SEM, EDX (punctual, line scan and mapping) and X-ray diffraction, besides some calculations of kp and n constants. The results of this thesis allow comparing the ?\' solvus (1210oC), solidus (1310oC) and liquidus (1360oC) temperatures obtained by Thermo-Calc with the ?\' solvus (1238oC), incipient melting (1281oC) and liquidus (1370oC) temperatures obtained by differential thermal analysis experiments of the MARM247(Nb) superalloy. The microstructure of the as-cast MAR-M247(Nb) superalloy is dendritic with W, Ti, Nb and Hf carbides in the interdendritic regions. The solution heattreatment at 1260°C for 8 hours was chosen as the ideal condition, whilst the aging heattreatment at 980°C for 80 hours presented the highest ?\' particle size. The material processed by laser melting technique showed cracks due to formation of low melting point ?/?\' eutectic regions. The microstructure of the NiCr, NiCrAl and NiCrAlY as clad deposits is dendritic with the ?-Ni(Cr) solid solution phase, besides pores and oxides/carbides. The NiCrAlY deposit has yttrium-rich phases. The NiCr sample heattreated at 1150oC for 50 hours didn\'t present evidences of segregation whilst the NiCrAl and NiCrAlY samples presented fine and uniform ?\' phase precipitated after the heattreatment at 1100 and 1150°C for 10 and 50 hours. The structure of the oxide layer of the MAR-M247(Nb) superalloy submitted to isothermal oxidation experiments at 1000°C for up to 216 hours has NiO in the outer layer, Cr2O3, TiO2, CoO, (Ni,Co)Cr2O4 spinels and W20O58 and HfO2 particles in the intermediate layer, and Al2O3 in the inner layer. Finally, it is possible to conclude that the microstructure and the properties of the MAR-M247(Nb) superalloy are modified when the processing routes (heat-treatment, laser cladding and isothermal oxidation) are changed.

Dans l’industrie de la verrerie, le laser cladding est une technique de rechargement très innovante permettant de déposer une couche très fine d’un alliage à base de nickel pour protéger les moules (utiles à la fabrication de bouteilles en verre) de la corrosion, de l’abrasion ainsi que de la fatigue thermique. La méthode utilisée ici (fusion de poudre projetée par laser) est très courante en fabrication additive. Cette étude s’intéresse à l’impact du rechargement sur le dépôt et les substrats en Cu-Ni-Al et en fonte GL. L’influence sur la microstructure ainsi que sur le comportement mécanique a pu être étudiée (MEB et microanalyses, dureté, contraintes résiduelles ...). Nous nous sommes focalisés sur l’apparition de défauts tels que le manque d’accroche lors du laser cladding sur du Cu-Ni-Al et sur la possible fissuration lors du rechargement sur de la fonte GL. Le but est bien sûr de s’affranchir de ces défauts. Il a notamment été mis en évidence que le manque d’accroche (cas du Cu-Ni-Al) est lié à la distribution gaussienne de la poudre qui atténue la puissance incidente du laser au niveau du pic de poudre. Le manque d'accroche n'est pas détecté sur le substrat en fonte en raison de sa forte absorptivité et de sa faible conductivité thermique. Néanmoins, des fissures peuvent être observées en raison de contraintes résiduelles thermiques et de la présence d'une zone affectée thermiquement. De plus, l’analyse statistique ANOVA a permis une optimisation des paramètres de rechargement de telle sorte à obtenir une accroche dans toute la section tout en respectant les préconisations géométriques données par les Établissements CHPOLANSKY pour le cordon. / In glass industry, the laser cladding is an innovative surfacing technique allowing to deposit a very thin layer of nickel to protect glass mold (useful for glass bottle production) against corrosion, abrasion and thermal fatigue. This method (powder fusion by projection) is well known in additive manufacturing. The aim of this work is to observe the impact of the laser cladding on the coating behavior but also on the Cu-Ni-Al and flake-graphite cast iron substrates. The microstructure and the mechanical properties were studied (SEM and microanalysis, microhardness, residual stress …) around the interface cladding/substrate. The work was also focused on the defects like lack of bonding but also on cracking behavior during surfacing on cast iron. The purpose was to prevent from those defects. This work showed that the lack of bonding to the Cu-Ni-Al substrate is due to the gaussian distribution of the powder which attenuates the input laser power at its peak. The lack of bonding is not detected on cast iron substrate thanks to its high absorptivity and low thermal conductivity. Nevertheless, cracks can be observed due to thermal residual stresses and the presence of a thermal affected zone. The ANOVA technique allowed us to optimize the processing parameters in order to obtain a perfect bonding and the geometry wanted by CHPOLANSKY Establishments.

The growing interest in increasing the wear resistance and hardness of surfaces that are in contact with abrasives or corrosive materials has inspired the development of several processes for creating protective coatings. In-situ laser cladding is one of the most promising of these processes. It enables the formation of a uniform coating by melting powder to form the desired composition from a pure powder component. In this research, pure Ti, graphite, and Fe are used for in-situ laser cladding on a steel substrate to form an Fe-TiC metal matrix composite (MMC). The effect of laser parameters on both the quality of the bonding and morphology of the in-situ-formed TiC iron-based composite clad are investigated. Results show that laser parameters play a crucial role in determining the clad quality and clad microstructure. Two combined parameters, effective energy and powder deposition density, are used to study the effect of laser parameters (i.e., laser power, scan speed and powder feed rate) on the clad properties. While results indicate that combined parameters help to determine the quality limit, laser process parameters need to be taken into account in order to study the clad microstructure. To increase the clad hardness and TiC volume fraction, C:Ti atomic ratio should increase from 45:55 to 55:45, and Fe percentages in the powder composition should decrease from 70 wt% to the 10 wt%. By varying the powder composition, a change in TiC morphology, clad microstructure and clad hardness occurs. The dilution effect is also considered in the interpretation of results. In order to estimate wear resistance, the ASTM G65-A procedure was selected to perform tests on various clad compositions. An increased wear resistance is seen when the volume fraction of TiC is increased.

The growing interest in increasing the wear resistance and hardness of surfaces that are in contact with abrasives or corrosive materials has inspired the development of several processes for creating protective coatings. In-situ laser cladding is one of the most promising of these processes. It enables the formation of a uniform coating by melting powder to form the desired composition from a pure powder component. In this research, pure Ti, graphite, and Fe are used for in-situ laser cladding on a steel substrate to form an Fe-TiC metal matrix composite (MMC). The effect of laser parameters on both the quality of the bonding and morphology of the in-situ-formed TiC iron-based composite clad are investigated. Results show that laser parameters play a crucial role in determining the clad quality and clad microstructure. Two combined parameters, effective energy and powder deposition density, are used to study the effect of laser parameters (i.e., laser power, scan speed and powder feed rate) on the clad properties. While results indicate that combined parameters help to determine the quality limit, laser process parameters need to be taken into account in order to study the clad microstructure. To increase the clad hardness and TiC volume fraction, C:Ti atomic ratio should increase from 45:55 to 55:45, and Fe percentages in the powder composition should decrease from 70 wt% to the 10 wt%. By varying the powder composition, a change in TiC morphology, clad microstructure and clad hardness occurs. The dilution effect is also considered in the interpretation of results. In order to estimate wear resistance, the ASTM G65-A procedure was selected to perform tests on various clad compositions. An increased wear resistance is seen when the volume fraction of TiC is increased.

Las aleaciones de titanio poseen una excelente resistencia mecánica específica combinada con una gran resistencia a la corrosión y oxidación. No obstante, su comportamiento frente al desgaste es pobre y limita su uso en muchas aplicaciones para la industrial naval, aeronáutica y petroquímica. En este trabajo se propone utilizar el recubrimiento por laser o "laser cladding" para depositar capas de material compuesto de matriz de Ti6Al4V reforzado con diferentes contenidos en peso de partículas cerámicas duras de carburo de titanio (TiC) con el fin de mejorar el comportamiento frente al desgaste. Se trata de un trabajo experimental complejo ya que el titanio posee una enorme reactividad con la atmosfera que dificulta enormemente su procesado por láser. Por este motivo, se ha diseñado una tabla de experimentación que permite estudiar el procesado por laser en varias etapas de complejidad creciente para analizar el efecto de las variables por separado. La experimentación de ha dividido en cuatro etapas: primero se analiza el efecto de las variables de procesado por laser para recubrir Ti6Al4V con polvo de Ti6Al4V y obtener la ventana de procesado, luego se ha estudiado el efecto de la adición de diferentes fracciones de TiC y se han fabricado recubrimientos por solape de cordones, tercero se caracteriza el comportamiento frente a desgaste en seco para determinar las condiciones óptimas de procesado, finalmente se estudia en profundidad las transformaciones metalúrgicas que ocurren en los recubrimientos considerados como óptimos con el fin de proponer posibles mejoras. Los resultados experimentales muestran que el procesado por laser de titanio requiere un estudio completo para optimizar las condiciones de procesado. Solo mediante un plan de experimentos adecuado ha sido posible triplicar la productividad del proceso y obtener recubrimientos de Ti6Al4V libres de defectos como grietas, poros y oxidación. En este sentido, el uso de helio como gas de protección supone una ventaja absoluta frente al argón por su mayor potencial de ionización para evitar la formación de plasma. / Candel Bou, JJ. (2012). ANÁLISIS MICROESTRUCTURAL DE RECUBRIMIENTOS COMPUESTOS DE CARBURO DE TITANIO Y MATRIZ DE TITANIO DEPOSITADOS POR LÁSER [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/14983 / Palancia