152 research outputs found
Elaboration de composites à matrice métallique d'alliages d'aluminium par projection à froid
Le procĂ©dĂ© de projection Ă froid (cold spray en anglais) est un procĂ©dĂ© fondĂ© sur l accĂ©lĂ©ration de particules qui restent Ă l Ă©tat solide pour former des dĂ©pĂŽts. L un des forts potentiels applicatifs de ce procĂ©dĂ© rĂ©side dans la rĂ©alisation de dĂ©pĂŽts composites car l'incorporation des particules cĂ©ramiques dans des poudres mĂ©talliques influence la microstructure et les propriĂ©tĂ©s des dĂ©pĂŽts. NĂ©anmoins, le principe de construction du dĂ©pĂŽt composite n est pas encore parfaitement Ă©tabli. En consĂ©quence, les recherches menĂ©es dans cette Ă©tude sur la fabrication de dĂ©pĂŽts composites s articulent autour de plusieurs domaines, Ă savoir : La science des matĂ©riaux avec des Ă©tudes sur l effet de la taille et de la teneur (15 vol.% - 60 vol.%) de la particule du renfort (SiC); La mĂ©canique des fluides avec des modĂ©lisations des vitesses des particules cĂ©ramiques (SiC) et alliage d aluminium (Al5056) et les simulations du comportement Ă la dĂ©formation de la particule; Les caractĂ©risations des dĂ©pĂŽts avec des analyses de microstructure et de microduretĂ©, de la cohĂ©sion du dĂ©pĂŽt et de comportement en frottement des dĂ©pĂŽts;Les rĂ©sultats montrent que la tempĂ©rature du gaz n'a aucun effet sur la teneur en SiC dans les dĂ©pĂŽts mais provoque une amĂ©lioration du rendement de dĂ©pĂŽt. La teneur en SiC dans les dĂ©pĂŽts composites d Al5056/SiCp augmente avec l augmentation de la teneur en SiC dans les poudres initiales. L ajout de SiC dans les dĂ©pĂŽts d Al5056 augmente la duretĂ© et amĂ©liore la rĂ©sistance Ă l'usure des dĂ©pĂŽts, et puis l amĂ©lioration dĂ©pend de la teneur en SiC dans les dĂ©pĂŽts composites. La force de cohĂ©sion des dĂ©pĂŽts augmente dans un premier temps avec l augmentation de la teneur en SiC puis diminue Ă partir d environ 26-27%. Les dĂ©pĂŽts composites renforcĂ©s par SiC-67 et SiC-27 ont une teneur en SiC semblable dans les dĂ©pĂŽts ; Pourtant la microduretĂ©, la force de cohĂ©sion et la rĂ©sistance Ă l'usure des dĂ©pĂŽts formĂ©s par Al5056/SiC-67 sont supĂ©rieures Ă celles des dĂ©pĂŽts construits par Al5056/SiC-27. Ce phĂ©nomĂšne relĂšve l importance de l Ă©nergie cinĂ©tique des particules renforts.Les rĂ©sultats expĂ©rimentaux ont montrĂ© que les particules de SiC ne se dĂ©forment pas plastiquement mais qu elles sont susceptibles de crĂ©er des cratĂšres sur le substrat ou le revĂȘtement dĂ©jĂ formĂ© ou encore rebondir ou bien de s insĂ©rer mĂ©caniquement dans le revĂȘtement dĂ©posĂ©. Finalement, un modĂšle eulĂ©rien a Ă©tĂ© dĂ©veloppĂ© pour prĂ©dire la vitesse critique Ă partir de la morphologie de l Ă©jection de matiĂšre au moment de l impact. Ce modĂšle a Ă©galement Ă©tĂ© Ă©tendu au dĂ©pĂŽt composite pour reprĂ©senter le procĂ©dĂ© d empilement des particules pendant la projection. Les rĂ©sultats calculĂ©s montrent la plus grande dĂ©formation des particules de la matrice grĂące Ă l impact des renforts.In cold spraying, particles are accelerated in the gas jet to achieve a high velocity and deposit on the substrate with a solid state. One of potential and important applications of cold spray is realizing the composite coatings. The incorporated ceramic particles in the composite coating can greatly influence the microstructure and properties of the coatings. The objective of this thesis was to investigate factors influencing the reinforcement content in the coatings and especially the formation mechanism in cold spraying. Al5056/SiC composite coatings were prepared by cold spraying. The effect of particle size and the reinforcement content in the powders on the reinforcement content in the coatings and thus on the microstructure and the properties of the coatings were studied. A search on the particle deformation and the formation mechanism of the composite coating was also carried out by using software of fluent and Abaqus.The results show that the addition of the SiC particles in the coating increases the hardness and improves the wear resistance of the coatings. However, the cohesion strength of the coatings first increases with the increase of the SiC content in the coating and then at a certain fraction, it decreases. Moreover, under the condition of having a similar SiC content in the coating, larger SiC particles lead to better properties of the coatings.Finally, an eulerian model was used for predicting the critical velocity by the morphology of the material jet. This model has also been extended to the composite model to demonstrate the built-up process of the composite coating during cold spraying. The calculation results show that the matrix particles deform more greatly after being impacted by the reinforcements.BELFORT-UTBM-SEVENANS (900942101) / SudocSudocFranceF
Etude sur fusion laser sélective de matériau céramique Zircone Yttriée
La fusion sĂ©lective par laser est un procĂ©dĂ© de la technologie de fabrication rapide de plus en plus utilisĂ© dans l industrie automobile, aĂ©ronautique, mĂ©dicale, etc. Selon le principe de la fabrication rapide, la piĂšce est fabriquĂ©e couche par couche en fusionnant et soudant les particules fines par laser. Actuellement, les principaux matĂ©riaux utilisĂ©s sont les mĂ©taux mĂ©talliques ou les polymĂšres. Le faible ou modeste point de fusion de ces matĂ©riaux conduit Ă une mise en Ćuvre par laser relativement facile. Cependant, en raison de leur point de fusion Ă©levĂ©, de la forte rĂ©sistance Ă haute tempĂ©rature et de la faible conductivitĂ© thermique, l utilisation de matĂ©riaux cĂ©ramiques est limitĂ©e dans la technologie de fusion laser sĂ©lective. Cette Ă©tude explore la fusion laser sĂ©lective de zircone stabilisĂ©e par yttrine avec un laser Ă fibre de longueur d onde d environ 1 m. L influence de diffĂ©rentes puissances de laser et de diffĂ©rentes vitesses de balayage sur la microstructure et la dĂ©formation de l Ă©chantillon a Ă©tĂ© Ă©tudiĂ©e, et la densitĂ© relative et la microduretĂ© ont Ă©tĂ© mesurĂ©es. Notamment, l effet de diffĂ©rentes tempĂ©ratures de prĂ©chauffage sur la microstructure sera Ă©tudiĂ©. En mĂȘme temps, la structure cristalline cĂ©ramique et la transformation des phases pendant le procĂ©dĂ© de prototypage rapide ont Ă©tĂ© analysĂ©es. Les rĂ©sultats expĂ©rimentaux montrent qu il est possible de fondre complĂštement de la poudre YSZ avec un laser Ă fibre NIR, et avec l optimisation des paramĂštres de fabrication, la densitĂ© relative de l Ă©chantillon peut atteindre 91 %. Il est inĂ©vitable de voir se former des fissures et des pores dans les piĂšces fabriquĂ©es du fait de l hĂ©tĂ©rogĂ©nĂ©itĂ© de la distribution de l Ă©nergie du laser. Cette distribution de l Ă©nergie peut ĂȘtre amĂ©liorĂ©e grĂące Ă l optimisation des paramĂštres ; les longueurs de fissure peuvent ĂȘtre contrĂŽlĂ©es et maĂźtrisĂ©es par un prĂ©chauffage du lit de poudre. Notamment, Ă haute tempĂ©rature (1500C, 2000C et 2500C) de prĂ©chauffage, la fissure verticale continue devient dĂ©sordonnĂ©e et courte. Une transformation de la structure monoclinique et cubique en structure tĂ©tragonale s est produite pendant le processus de fabrication.Selective laser melting is a rapid manufacturing process coming from the rapid prototyping technology, which is widely used in the automotive, aeronautical, medical industry etc. According to the principle of rapid manufacturing, the piece is manufactured layer by layer through the laser sintering or melting the fine powder. Currently, the main powder materials used are metal or polymer materials. The low melting point of these materials facilitates the melting process. However, duo to the high melting point, strong strength at high temperature and low thermal conductivity the application of ceramic materials is limited in the technology of selective laser melting. In this study, selective laser melting of the ceramic yttria stabilized zirconia by a 1 m wavelength fiber laser was explored. The influence of different laser powers and different scanning velocities on the microstructure and the deformation were analyzed, then the micro-hardness and relative density were measured. In particular, the effect of different preheat temperatures on microstructure was investigated. At the same time, the crystal structure and phase transformation during the fabrication were analyzed. Experimental results show that YSZ powder can be completely melted by the near IR fiber laser. With the optimization of the manufacturing parameters, the relative density of sample could reach 91 %. The forming of cracks and pores in the manufactured parts is rarely avoid due to the heterogeneity of distribution of energy. The energy distribution could be improved by optimizing the parameters and the crack lengths can be controlled by preheating the powder bed. In particular, the high temperature (1500 , 2000 and 2500 ) lead the continuous vertical crack becomes messy and short. The transformation of monoclinic and cubic crystal to tetragonal crystal can be observed during the fabrication.BELFORT-UTBM-SEVENANS (900942101) / SudocSudocFranceF
Programmation robotique en utilisant la méthode de maillage et la simulation thermique du procédé de la projection thermique
L objectif de cette Ă©tude est d amĂ©liorer l extension du logiciel de programmation hors-ligne RobotStudio existante et de dĂ©velopper une nouvelle stratĂ©gie pour gĂ©nĂ©rer la trajectoire du robot par rapport aux paramĂštres essentiels de projection thermique. Notamment, l historique de la tempĂ©rature par rapport Ă la trajectoire gĂ©nĂ©rĂ©e est prise en compte dans cette Ă©tude.L extension logicielle Thermal Spray Toolkit (TST) intĂ©grĂ©e dans le cadre de RobotStudio est spĂ©cialement dĂ©veloppĂ©e pour gĂ©nĂ©rer la trajectoire du robot en projection thermique. L amĂ©lioration de l extension TST dans la nouvelle version de RobotStudio est mise au point sur deux modules principaux :PathKit : gĂ©nĂ©ration de la trajectoire sur des piĂšces complexes.ProfileKit : modĂ©lisation du cordon singulier du dĂ©pĂŽt et prĂ©diction de son Ă©paisseur en fonction des paramĂštres opĂ©ratoires.Les dĂ©ficiences existantes de l extension TST impliquent de mettre en Ćuvre une mĂ©thode plus avancĂ©e qui permettra de gĂ©nĂ©rer la trajectoire du robot en utilisant le maillage pour le calcul d Ă©lĂ©ment finis. Ainsi, l opĂ©ration de projection thermique pourra ĂȘtre menĂ©e. Dans cette Ă©tude, la mĂ©thodologie de maillage est introduite afin de fournir une stratĂ©gie de choix de points de trajectoire et l obtention d orientations de ces points de trajectoire sur la surface Ă revĂȘtir. Un module dit MeshKit est donc ajoutĂ© dans l extension TST afin de lui apporter ces fonctionnalitĂ©s nĂ©cessaires.Un couplage entre la trajectoire du robot et la rĂ©partition de chaleur du substrat a Ă©tĂ© dĂ©veloppĂ©, ce qui permet d Ă©tudier l Ă©volution de tempĂ©rature pendent le processus de projection thermique.The objective of this study is to improve the add-in package of off-line programming software RobotStudio and to develop a new strategy for generating the robot trajectory according to the kinematic parameters of thermal spraying. The computed temperature evolution relative to the generated robot trajectory on the coating surface is also considered in this study.The add-in package Thermal Spray Toolkit (TST) integrated in RobotStudio is developed to generate the robot trajectory for thermal spraying. The improved TST for new version of RobotStudio is composed of two principle modules:PathKit: generation of robot trajectory on the free-form coating surface.ProfileKit: modeling the coating profile and prediction the coating thickness based on kinematic parameters.The existing deficiency of TST leads to the development of an advanced robot trajectory generation methodology. In this study, the new approach implements the robotic trajectory planning in an interactive manner between RobotStudio and the finite element analysis software (FES). It allows rearranging the imported node created on the surface of workpiece by FES and in turns generating the thermal spraying needed robot trajectories.A coupling between the robot trajectory and the heat distribution on the substrate has been developed, which allows analyzing the temperature evolution during the thermal spray process, it helps to minimize thermal variations on the substrate and to select the appropriate execution sequence of trajectory.BELFORT-UTBM-SEVENANS (900942101) / SudocSudocFranceF
Effet de projection de pellettes bioxycarbonĂ©es sur la qualitĂ© de revĂȘtements Ă©laborĂ©s par la projection thermique
La technologie de projection plasma atmosphĂ©rique (APS) est largement utilisĂ©e pour des applications industrielles. Les revĂȘtements Ă©laborĂ©s par APS prĂ©sentent gĂ©nĂ©ralement certains dĂ©fauts. Les travaux effectuĂ©s dans cette Ă©tude ont consistĂ© Ă Ă©tudier et Ă dĂ©velopper un nouveau moyen pour assurer Ă la fois un refroidissement efficace au cours de procĂ©dĂ© de projection APS et une adaptation des conditions superficielles en vue d Ă©laborer des revĂȘtements de haute qualitĂ©. Ce moyen consiste Ă la projection de glace carbonique (glace sĂšche ou dioxyde de carbone solide) en association avec la projection plasma. Des simulations numĂ©riques ont Ă©tĂ© rĂ©alisĂ©es, qui ont permis de constater que les dimensions de la buse de projection de glace carbonique, la pression du gaz propulsif, et les propriĂ©tĂ©s des pellets de CO2 influencent sensiblement la vitesse des pellets de CO2. A partir de ces Ă©lĂ©ments, des dimensions optimales ont Ă©tĂ© Ă©valuĂ©es. Afin d examiner l effet de la projection de glace carbonique sur les revĂȘtements rĂ©alisĂ©s par projection thermique, plusieurs types de matĂ©riaux ont Ă©tĂ© considĂ©rĂ©s, trois mĂ©talliques (acier, CoNiCrAlY et aluminium pur) et trois cĂ©ramiques (Al2O3, Cr2O3 et ZrO2-Y2O3). Les microstructures des revĂȘtements metalliques rĂ©alisĂ©s avec projection de glace sĂšche prĂ©sentent moins d'oxydes et moins de porositĂ© par rapport Ă ceux dĂ©posĂ©s par APS classique. Dans certains cas l adhĂ©rence peut aussi ĂȘtre amĂ©liorĂ©e. Pour les revĂȘtements cĂ©ramiques, une rĂ©duction de la porositĂ© ainsi qu une amĂ©lioration significative de l adhĂ©rence des revĂȘtements ont Ă©tĂ© constatĂ©s. Pour le dĂ©pĂŽt de ZrO2-Y2O3, la rĂ©sistance aux chocs thermiques a Ă©tĂ© amĂ©liorĂ©e en utilisant des paramĂštres spĂ©cifiques. La projection de CO2 peut lĂ©gĂšrement dĂ©former la surface des substrats de faible duretĂ©, et nettoyer les pollutions superficielles sur le substrat et conduire Ă une contrainte de compression plus Ă©levĂ©e et Ă un refroidissement efficace. Il est Ă noter toutefois qu un problĂšme de condensation de la vapeur d eau peut intervenir en cas de refroidissement du substrat trop important.The technology of atmospheric plasma spraying (APS) is widely used for industrial applications. The coatings produced by APS generally show defects. The work was conducted to investigate and develop a new method to ensure both an effective cooling during the APS process and the adaptation of the surface condition in order to develop high quality coatings. This solution is dry ice (CO2) blasting in combination with thermal spraying. Firstly, numerical simulations were carried out, which revealed that the nozzle size of dry ice blasting, the propellant pressure and the properties of CO2 pellets, significantly affect the velocity of CO2 pellets. From these elements, the optimal dimensions were evaluated. To examine the effects of dry ice blasting on the coatings produced by thermal spraying, several types of materials were considered, three metals (steel, CoNiCrAlY and pure aluminum) and three ceramics (Al2O3, Cr2O3 and ZrO2-Y2O3). The microstructure of metal coatings produced with dry ice blasting show fewer oxides and less porosity compared to those deposited by conventional APS. In some cases the adhesion can be improved. Regarding ceramic coatings, a reduction in porosity and a significant improvement in the coating adhesion were observed. For the deposition of ZrO2-Y2O3, an improvement in thermal shock resistance was achieved using specific parameters. Dry-ice blasting may slightly impact the surface of the substrates with low hardness and could clean the surface pollutions on the substrate and lead to a higher compressive stress and an effective cooling. However, it is noted that the problem of the condensation of water vapor can occur in case of intense cooling of the substrate.BELFORT-UTBM-SEVENANS (900942101) / SudocSudocFranceF
Modélisation des propriétés thermomécaniques effectives de dépÎts élaborés par projection thermique
Dans la prĂ©sente Ă©tude, la conductivitĂ© thermique et le module d'Ă©lasticitĂ© de revĂȘtementsd YPSZ Ă©laborĂ©s par projection plasma ont Ă©tĂ© prĂ©dits par modĂ©lisations numĂ©riques 2D et3D de type diffĂ©rences finies et Ă©lĂ©ments finis.L'influence de la rĂ©solution d'image, de la taille et de la valeur du seuil sur les propriĂ©tĂ©sprĂ©dites du revĂȘtement a Ă©tĂ© Ă©tudiĂ©e. En outre, les effets de la mĂ©thode numĂ©rique et du typede condition aux limites ont Ă©tĂ© Ă©tudiĂ©s. En particulier, la quantification de l'effet Knudsen(effet de rarĂ©faction) sur le transfert de chaleur Ă travers une structure poreuse a Ă©tĂ© rĂ©alisĂ©epar modĂ©lisation numĂ©rique en combinaison avec l'analyse d'image. Les conductivitĂ©seffectives obtenues par modĂ©lisation 3D s'avĂšrent plus Ă©levĂ©es que celles obtenues en 2D, etaussi en meilleur accord avec les rĂ©sultats mesurĂ©s. Une corrĂ©lation 2D/3D a Ă©tĂ© trouvĂ©epour la modĂ©lisation de la conductivitĂ© thermique : cette corrĂ©lation permet de prĂ©dire lesvaleurs 3D Ă partir des valeurs calculĂ©es en 2D.In the present study, the thermal conductivity and elastic modulus of thermal spray YPSZcoatings were predicted by 2D and 3D finite differences and finite elements numericalmodeling based on cross-sectional images.The influence of the image resolution, size and threshold on the predicted properties of thecoating was studied. Moreover, the effects of the numerical method and of the boundarycondition were investigated. In particular, the quantification of the Knudsen effect(rarefaction effect) on the heat transfer through a porous structure was realized by numericalmodeling in combination with image analysis. The predicted thermal conductivities obtainedby 3D modeling were found to be higher than those obtained by 2D modeling, and in betteragreement with the measured results. A 2D/3D correlation was sucessfully found for themodeling of thermal conductivity: this correlation allows predicting 3D computed valuesfrom 2D ones.BELFORT-UTBM-SEVENANS (900942101) / SudocSudocFranceF
RĂ©alisation et caractĂ©risation des revĂȘtements Ă base magnĂ©sium Ă©laborĂ©s par projection Ă froid
Le procĂ©dĂ© de projection Ă froid a dĂ©montrĂ© ses avantages uniques dans la prĂ©paration de revĂȘtements mĂ©talliques, composites et cĂ©ramiques. Parmi ces revĂȘtements, ceux constituĂ©s de magnĂ©sium pur ou de composites Ă matrice mĂ©tallique Ă base de magnĂ©sium font partie des matĂ©riaux les plus prometteurs en raison de leur excellente rĂ©sistance spĂ©cifique. Pourtant, les mĂ©canismes de fabrication, par ce procĂ©dĂ© de projection, des revĂȘtements magnĂ©sium et composites Ă base de magnĂ©sium n'ont pas Ă©tĂ© Ă©tudiĂ©s. C est le sujet de cette thĂšse. Les recherches menĂ©es dans cette Ă©tude s articulent autour de plusieurs domaines, Ă savoir: La science des matĂ©riaux avec des Ă©tudes sur l effet de la granulomĂ©trie des particules de magnĂ©sium, l effet de la taille et de la teneur (15% vol. - 60 % vol.) des particules de renforcement (SiC) ; La mĂ©canique des fluides avec des modĂ©lisations de gĂ©omĂ©trie de buse, d Ă©coulement de gaz et des vitesses des particules de magnĂ©sium et alliage de magnĂ©sium (AZ91D) ; Les caractĂ©risations des dĂ©pĂŽts avec des analyses de microstructure et des mesures de microduretĂ©, d adhĂ©rence et de comportement au frottement des revĂȘtements;Les rĂ©sultats montrent que la projection Ă froid peut ĂȘtre utilisĂ©e pour fabriquer des revĂȘtements de magnĂ©sium purs ou composites sans aucune oxydation ou transformation de phase. La taille de ces particules doit rester dans une fourchette acceptable pour Ă©galer la vitesse critique (entre 653 m s-1 et 677 m s-1) permettant la dĂ©position. Concernant plus spĂ©cifiquement les rĂ©sultats sur les revĂȘtements de magnĂ©sium pur, le maximum de rendement de dĂ©pĂŽt est obtenu par projection d une poudre de granulomĂ©trie comprise entre 22 m et 64 m. L adhĂ©rence atteint 11.6 +- 0.5 MPa lorsque le substrat est prĂ©chauffĂ© Ă 200 oC. Pour le cas des revĂȘtements AZ91D, la construction du dĂ©pĂŽt s effectue par effet de verrouillage mĂ©canique. Le type de frottement observĂ© sur ces revĂȘtements est une usure adhĂ©sive. Dans les revĂȘtements composites d AZ91D SiC, la teneur en particules de renforcement SiC prĂ©sentes dans le dĂ©pĂŽt diminue avec leur taille dĂ» Ă l'effet onde de choc . Le rendement de dĂ©pĂŽt augmente avec la teneur en SiC de 15 vol.% Ă 30 vol.%, puis diminue au-delĂ de 30 vol%. Le type de frottement correspond Ă une usure par abrasion.Cold spraying has shown unique advantages in preparing coatings of metal, composite and ceramic. However, the deposition mechanism of magnesium and magnesium-based composite coatings fabricated using cold spraying was not researched although magnesium and metallic matrix composites based magnesium have drawn more and more attention due to their excellent specific strength. Therefore, the deposition mechanism of magnesium and magnesium-based composite coating has been studied in this study. The research carried out in this study involves several fields:Effect of the particle velocity of magnesium particles on the deposition efficiency, microstructure, microhardness and bonding strength of coatings; Effect of the particle size of magnesium particles on the deposition efficiency and microstructure of coatings;Effect of the substrate preheating on the microstructure, microhardness and bonding strength of coatings;Effect of the particle velocity of magnesium alloy (AZ91D) particles on the deposition efficiency, microstructure, and frictional behavior of coatings;Effect of the particle size of strengthening phrase (SiC) on the microstructure, bonding strength and frictional behavior of coatings;Effect of the particle content (15 vol.% - 60 vol.%) of strengthening phrase (SiC) on the microstructure, bonding strength and frictional behavior of coatings.The results show that cold spraying can be used to fabricate magnesium and magnesium-based coatings without any oxidation or phase transformation. The critical velocity of magnesium particles is 653 m s-1- 677 m s-1. Magnesium particles with a size too large or too small are not suitable to the deposition. The maximum of deposition efficiency of magnesium particles are obtained using the powder with a size range of 22-64 m. The maximum of bonding strength between magnesium coatings and substrates is 11.6 +- 0.5 MPa as the substrate is preheated at 200oC. The deposition of AZ91D coatings is due to the effect of mechanical interlocking. And the friction type of AZ91D coatings is adhesive wear. The friction type of AZ91D SiC composite coatings turn to be abrasive wear. The SiC content in composite coatings decreases as the SiC particle size decreases due to the effect of bow shock. The deposition efficiency of AZ91D and SiC mixed powder increases as the SiC content increases from 15 vol.% to 30 vol.%, and then decreases as the SiC content increases from 30 vol% to 60 vol.%.BELFORT-UTBM-SEVENANS (900942101) / SudocSudocFranceF
Preparation and characterization of magnesium coating deposited by cold spraying
Magnesium (Mg) and its alloys have a great potential as structural materials
due to their beneficial combination of high strength to weight ratio, high
thermal conductivity and good machinability. However, few literatures about Mg
coatings fabricated by cold spraying can be found. In this study, Mg coatings
were fabricated by cold spraying, and the microstructure, phase structure,
oxygen content and microhardness of the coating prepared under different main
gas temperatures were investigated. The critical velocity of the particle was
evaluated through numerical simulations. The particle deformation behavior and
bonding mechanism were discussed. The result of the oxygen content test shows
that the oxygen contents of the coatings did not increase comparing with that
of the feedstock powder. The simulation results show that the critical velocity
of Mg particles was in a range of 653 m/s to 677 m/s. The observation of the
coating fracture morphology shows that the formation of the coating was due to
the intensive plastic deformation and mechanical interlocking. The
microhardness of the coating increased with the increase of the main gas
temperature from 350oC to 450oC due to the decrease of the coating porosity.Comment: 20 pages, 9 figur
Achieving ultra-high strength and ductility in Mgâ9Alâ1Znâ0.5Mn alloy via selective laser melting
Fabrication of the Mgâ9Alâ1Znâ0.5Mn alloy with excellent mechanical performance using selective laser melting (SLM) technology is quite difficult owing to the poor weldability and low boiling point. To address these challenges and seek the optimal processing parameters, response surface methodology was systematically utilized to determine the appropriate SLM parameter combinations. Mgâ9Alâ1Znâ0.5Mn sample with high relative density (99.5 â± â0.28%) and favorable mechanical properties (microhardness â= â95.6 â± â5.28 HV0.1, UTS â= â370.2 âMPa, and At â= â10.4%) was achieved using optimized SLM parameters (P â= â120 âW, v â= â500 âmm/s, and h â= â45 âÎŒm). Sample âis dominated by a random texture and microstructure is primarily constituted by quantities of fine equiaxed grains (α-Mg phase), a small amount of ÎČ-Al12Mg17 structures (4.96 âvol%, including spherical: [21ÂŻ1ÂŻ0]α// [111]ÎČ and long lath-like: [21ÂŻ1ÂŻ0]α// [11ÂŻ5]ÎČ or [1ÂŻ011]α// [32ÂŻ1ÂŻ]ÎČ), and some short rod-shaped Al8Mn5 nanoparticles. Benefiting from grain boundary strengthening, solid solution strengthening, and precipitation hardening of various nanoparticles (ÎČ-Al12Mg17 and Al8Mn5), high-performance Mgâ9Alâ1Znâ0.5Mn alloy biomedical implants can be fabricated. Precipitation hardening dominates the strengthening mechanism of the SLM Mgâ9Alâ1Znâ0.5Mn alloy.</p
One step electrochemical fabrication of high performance Ni@Fe-doped Ni(oxy)hydroxide anode for practical alkaline water electrolysis
Oxygen evolution reaction (OER) is a rate-determining process in alkaline water electrolysis (AWE). Herein, we report a novel one-step oxidation-electrodeposition (OSOE) approach to generate core@shell nanoarrays-based AWE electrode with outstanding OER performances: an overpotential of 245 mV at 10 mA cmâ2 (Tafel slope: 37 mV decâ1), and excellent stability under huge current densities. Moreover, the alkaline (AEL) cell equipped with NM-OSOE-23 anode recorded significant performance improvement of 200 mV lower voltage (2 A cmâ1) compared with a similar cell used bare Ni mesh as an anode, which was contributed by notable enhancements of interface contact, anodic charge transfer, and mass transfer. These promising results are attributed to the constructed specific core@shell Ni@Fe-doped Ni(oxy)hydroxide nanoarray architecture on commercial nickel mesh. This study demonstrates this first reported OSOE can be commercialized to make highly efficient anodes enabling next-generation AWE
Selective laser melting of tungsten carbide reinforced maraging steel composite
In this work, tungsten carbide (WC) reinforced maraging steel matrix composites were in-situ manufactured by selective laser melting (SLM) from powder mixture. The SLM processed samples presented high relative density (over 99%) with a homogenous distribution of WC. The as-fabricated surface quality of SLM processed samples was improved significantly by the addition of WC. Focused ion beam and transmission electron microscopy were employed to characterize the interfacial properties between tungsten carbide and steel matrix. The elemental analysis indicates that metallurgical bonding appears at interfacial region due to the diffusion. Tensile behavior of SLM processed maraging steel was different from their composite with several WC contents
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