The primary goals of the research in this dissertation are to perform a systematic study to identify and understand the fundamental cause of prolonged processing time during transient liquid phase bonding of difficult-to-bond single crystal Ni-base materials, and use the acquired knowledge to develop an effective way to reduce the isothermal solidification time without sacrificing the single crystalline nature of the base materials. To achieve these objectives, a multi-scale numerical modeling approach, that involves the use of a 2-D fully implicit moving-mesh Finite Element method and a Cellular Automata method, was developed to theoretically investigate the cause of long isothermal solidification times and determine a viable way to minimize the problem. Subsequently, the predictions of the theoretical models are experimentally validated. Contrary to previous suggestions, numerical calculations and experimental verifications have shown that enhanced intergranular diffusivity has a negligible effect on solidification time in cast superalloys and that another important factor must be responsible. In addition, it was found that the concept of competition between solute diffusivity and solubility as predicted by standard analytical TLP bonding models and reported in the literature as a possible cause of long solidification times is not suitable to explain salient experimental observations. In contrast, however, this study shows that the problem of long solidification times, which anomalously increase with temperature is fundamentally caused by departure from diffusion controlled parabolic migration of the liquid-solid interface with holding time during bonding due to a significant reduction in the solute concentration gradient in the base material. Theoretical analyses showed it is possible to minimize the solidification time and prevent formation of stray-grains in joints between single crystal substrates by using a composite powder mixture of brazing alloy and base alloy as the interlayer material, which prior to the present work has been reported to be unsuitable. This was experimentally verified and the use of the composite powder mixture as interlayer material to reduce the solidification time and avoid stray-grain formation during TLP bonding of single crystal superalloys has been reported for the first time in this research.

The primary goals of the research in this dissertation are to perform a systematic study to identify and understand the fundamental cause of prolonged processing time during transient liquid phase bonding of difficult-to-bond single crystal Ni-base materials, and use the acquired knowledge to develop an effective way to reduce the isothermal solidification time without sacrificing the single crystalline nature of the base materials. To achieve these objectives, a multi-scale numerical modeling approach, that involves the use of a 2-D fully implicit moving-mesh Finite Element method and a Cellular Automata method, was developed to theoretically investigate the cause of long isothermal solidification times and determine a viable way to minimize the problem. Subsequently, the predictions of the theoretical models are experimentally validated. Contrary to previous suggestions, numerical calculations and experimental verifications have shown that enhanced intergranular diffusivity has a negligible effect on solidification time in cast superalloys and that another important factor must be responsible. In addition, it was found that the concept of competition between solute diffusivity and solubility as predicted by standard analytical TLP bonding models and reported in the literature as a possible cause of long solidification times is not suitable to explain salient experimental observations. In contrast, however, this study shows that the problem of long solidification times, which anomalously increase with temperature is fundamentally caused by departure from diffusion controlled parabolic migration of the liquid-solid interface with holding time during bonding due to a significant reduction in the solute concentration gradient in the base material. Theoretical analyses showed it is possible to minimize the solidification time and prevent formation of stray-grains in joints between single crystal substrates by using a composite powder mixture of brazing alloy and base alloy as the interlayer material, which prior to the present work has been reported to be unsuitable. This was experimentally verified and the use of the composite powder mixture as interlayer material to reduce the solidification time and avoid stray-grain formation during TLP bonding of single crystal superalloys has been reported for the first time in this research.

L'axe de recherche suivi dans cette thèse comprend principalement. L'élaboration, les caractérisations structurale par rayons X (XRD), microstructurale par microscopies électroniques (SEM et EBSD), chimique (EDS et EPMA) et mécanique (essais de traction et dureté) de jonctions de pièces d'acier au carbone à travers le procédé appelé ‘Transient Liquid Phase Bonding' (TLPB), en utilisant comme matériel d'apport des rubans amorphes des systèmes Fe-B-Si et Fe-B, et des feuilles de Cu.Les jonctions TLPB ont été obtenus en chauffant les pièces à unir à une température de 1300ºC, qui est maintenue pendant 7 min, en même temps qu'on applique une pression de 5 MPa.Les résultats EBSD et SEM montrent que lorsque des rubans amorphe de Fe-B-Si sont utilisés comme matériel d'apport, on observe dans la zone de jonction des tubes une microstructure caractérisée par des grains de ferrite alors que dans la zone affectée par la chaleur (Heat Affected Zone, HAZ), on observe une microstructure ferritique-perlitique. Les grains de ferrite de la jonction ne sont généralement pas partagés avec ceux de la HAZ et sont clairement délimités par des bords de grains. Grâce aux profils de compositions obtenus par EDS et EPMA, on peut montrer que le jonction s'enrichit en Si et s'appauvrit en Mn. Cette microsegregation de Si et Mn produite par le procédé TLPB fait de la jonction une région de formation prématurée de ferrite au bord des grains de l'austénite de la HAZ. Après l'austénite de la HAZ se transforme au refroidissement pour former une structure ferritique/perlitique, qui contraste avec la jonction. Les propriétés mécaniques, montrent que la fracture se produit dans la HAZ loin de la jonction. Les mesures de dureté dans la jonction et la HAZ sont en accord avec les microstructures observées.Une étude complémentaire sur des régions avec une solidification isothermique incomplète montre que dans une première étape la phase primaire qui solidifie est pareille à celle du procédé TLPB et ensuite d'autre phases apparaissent. La phase métastable Fe23B6, a pu être détecté par une expérience de microdiffraction XRD (ID27, ESRF en Grenoble).Lorsque l'on utilise des rubans amorphes de Fe-B comme matériel d'apport, on ne distingue pas clairement les microstructure de la jonction de celle de la HAZ. Les grains de ferrite de la jonction sont partagés avec ceux de la HAZ et on peut visualiser une solidification épitaxiale dans la jonction à partir des grains de la HAZ. Les propriétés mécaniques, montrent que la résistance à la traction est d'au moins 88% de la valeur des pièces métalliques. Dans ce cas la rupture se produit à la jonction bien que les valeurs de dureté correspondent à celle attendus pour les microstructures présentes.Finalement , lorsque une feuille de Cu est utilisé comme matériaux d'apport on observe des microstructures similaires pour la jonction et la HAZ. Près de la surface on observe une porosité du à l'effet Kirkendall (le Cu de la jonction diffuse dans la pièce métallique plus rapidement que le Fe de celle-ci diffuse dans la jonction ce qui génère un flux de lacunes vers la jonction d'où sa porosité). Cet effet est moins marqué (moins de porosité) loin des bords car la pression au niveau de la jonction est plus grande. Ceci indique la haute sensibilité de l'effet Kirkendall avec la pression. Les propriétés mécaniques montrent que la résistance à la traction est d'au moins 85% de la valeur des pièces métalliques et la rupture se produit à la jonction. La rupture est lié à la présence de phases secondaires du à l'abondance de régions avec une solidification isothermique incomplète (ces régions cèdent sous tractions ce qui réduit l'aire efficace lors de l'essai entrainant la rupture par surcharge). Les mesures de dureté dans la jonction et la HAZ sont en accord avec les microstructures observées. / The main scientific activities carried out in this thesis includes: The structural characterization by X-Ray diffraction (XRD), microstructure analysis by electron microscopy (SEM and EBSD), chemical analysis (EDS and EPMA) and mechanical testing - tensile and hardness tests - of the joints of bonded carbon steel parts by means of the Transient Liquid Phase Bonding (TLPB) process, using as filler materials amorphous ribbons of Fe-B and Fe-Si-B systems, and Cu foils.The TLPB bonded joints were obtained by heating the assembly to a temperature of 1300ºC, which is maintained for 7 min, at the same time a pressure of 5 MPa is applied.The results obtained both by SEM and EBSD show that when amorphous Fe-Si-B ribbons are used as filler material, at the joint of the bonded parts a microstructure consisting of ferrite grains is observed, in contrast with ferritic-pearlitic microstructure at the heat affected zone (HAZ).The ferrite grains at the joint are not generally shared with those of the HAZ, and are clearly delimited by grain boundaries. The composition profiles obtained both by EDS and EPMA show that the joint is enriched in Si and is depleted in Mn. During cooling, this microsegregation of Mn and Si produced by the TLPB makes the joint a region where ferrite is formed prematurely at austenite grains boundaries of the HAZ. Afterwards, the austenite of the HAZ transforms to form a ferritic/pearlitic microstructure, which contrasts with that of the joint. The tensile tests of specimens from the bonded parts show that the fracture occurs in the HAZ, far from the junction. Hardness measurements both at the joint and at the HAZ are consistent with the observed microstructures.A complementary study at the joint was carried out where the isothermal solidification completion was not achieved. During cooling, at a first stage the phase which solidifies is the same than that during the TLPB process. Finally, the appearance of other phases takes place. The metastable phase Fe23B6 was detected by X-Ray microdiffraction (ID27, ESRF at Grenoble).When amorphous Fe-B ribbons are used as filler material, there is no clear distinction between the microstructure at the joint and at the HAZ. The ferrite grains at the joint are shared with those of the HAZ, and epitaxial solidification of these grains can be visualized from the grains of the HAZ.When tensile tested, the bonded parts attain at least 88% of the ultimate tensile strength (UTS) of the base metal. In this case, fracture occurred at the joint, although the values of hardness correspond to those expected for the observed microstructures.Finally, when Cu foils are used as filler material, the microstructure observed at the joint is similar to that of the HAZ. Close to the outer surface, porosity due to Kirkendall effect is observed (the Cu of the joint diffuses into the base metal faster than the Fe into the joint, which generates a flow of vacancies towards the joint, thus developing porosity). This effect is less pronounced (less porosity) away from the outer surface where the pressure at the joint is larger. This indicates the high sensitivity of the Kirkendall effect with pressure. The tensile test shows that the joint attains at least 85% of the UTS of the base metal, and that it fails at the joint. The latter is related to the abundance of secondary phases due to an incomplete isothermal solidification (these areas - with lower strength compared with the base metal - fail before under traction, which reduces the effective area during the test, resulting in an overload failure). Hardness measurements at the joint and at the HAZ are consistent with the observed microstructres.

No / Transient liquid phase (TLP) brazing of Mg–AZ31 alloy and Ti–6Al–4V alloy was performed using double Ni and Cu sandwich foils. Two configurations were tested; first, Mg–AZ31/Cu–Ni/Ti–6Al–4V and second, Mg–AZ31/Ni–Cu/Ti–6Al–4V. The effect of set-up configuration of the foils on microstructural developments, mechanical properties and mechanism of joint formation was examined. The results showed that different reaction layers formed inside the joint region depending on the configuration chosen. The formation of e phase (Mg), r (CuMg2), d (Mg2Ni) and Mg3AlNi2 was observed in both configurations. Maximum shear strength obtained was 57 MPa for Mg–AZ31/Ni–Cu/Ti–6Al–4V configuration and in both configurations, the increase in bonding time resulted in a decrease in joint strength to 13 MPa. The mechanism of joint formation includes three stages; solid state diffusion, dissolution and widening of the joint, and isothermal solidification. / The authors would like to acknowledge The German Jordanian University (GJU), and NSERC Canada for the financial support for this research.

The problem of inaccurate measurement techniques for quantifying isothermal solidification kinetics during transient liquid phase (TLP) bonding in binary and ternary systems; and resulting uncertainty in the accuracy of analytical and numerical models has been addressed by the development of a new technique using differential scanning calorimetry (DSC). This has enabled characterization of the process kinetics in binary and ternary solid/liquid diffusion couples resulting in advancement of the fundamental theoretical understanding of the mechanics of isothermal solidification. The progress of isothermal solidification was determined by measuring the fraction of liquid remaining after an isothermal hold period of varying length. A 'TLP half sample', or a solid/liquid diffusion couple was setup in the sample crucible of a DSC enabling measurement of the heat flow relative to a reference crucible containing a mass of base metal. A comparison of the endotherm from melting of an interlayer with the exotherm from solidification of the residual liquid gives the fraction of liquid remaining. The Ag-Cu and Ag-Au-Cu systems were employed in this study. Metallurgical techniques were used to compliment the DSC results. The effects of sample geometry on the DSC trace have been characterized. The initial interlayer composition, the heating rate, the reference crucible contents, and the base metal coating must be considered in development of the experimental parameters. Furthermore, the effects of heat conduction into the base metal, baseline shift across the initial melting endotherm, and the exclusion of primary solidification upon cooling combine to systematically reduce the measured fraction of liquid remaining. These effects have been quantified using a modified temperature program, and corrected using a universal factor. A comparison of the experimental results with the predictions of various analytical solutions for isothermal solidification reveals that the moving interface solution can accurately predict the interface kinetics given accurate diffusion data. The DSC method has been used to quantify the process kinetics of isothermal solidification in a ternary alloy system, with results compared to a finite difference model for interface motion. The DSC results show a linear relationship between the interface position and the square root of the isothermal hold time. While the numerical simulations do not agree well with the experimental interface kinetics due to a lack of accurate thermodynamic data, the model does help develop an understanding of the isothermal solidification mechanics. Compositional shift at the solid/liquid interface has been measured experimentally and compared with predictions. The results show that the direction of tie-line shift can be predicted using numerical techniques. Furthermore, tie-line shift has been observed in the DSC results. This study has shown that DSC is an accurate and valuable tool in the development of parameters for processes employing isothermal solidification, such as TLP bonding.

The problem of inaccurate measurement techniques for quantifying isothermal solidification kinetics during transient liquid phase (TLP) bonding in binary and ternary systems; and resulting uncertainty in the accuracy of analytical and numerical models has been addressed by the development of a new technique using differential scanning calorimetry (DSC). This has enabled characterization of the process kinetics in binary and ternary solid/liquid diffusion couples resulting in advancement of the fundamental theoretical understanding of the mechanics of isothermal solidification. The progress of isothermal solidification was determined by measuring the fraction of liquid remaining after an isothermal hold period of varying length. A 'TLP half sample', or a solid/liquid diffusion couple was setup in the sample crucible of a DSC enabling measurement of the heat flow relative to a reference crucible containing a mass of base metal. A comparison of the endotherm from melting of an interlayer with the exotherm from solidification of the residual liquid gives the fraction of liquid remaining. The Ag-Cu and Ag-Au-Cu systems were employed in this study. Metallurgical techniques were used to compliment the DSC results. The effects of sample geometry on the DSC trace have been characterized. The initial interlayer composition, the heating rate, the reference crucible contents, and the base metal coating must be considered in development of the experimental parameters. Furthermore, the effects of heat conduction into the base metal, baseline shift across the initial melting endotherm, and the exclusion of primary solidification upon cooling combine to systematically reduce the measured fraction of liquid remaining. These effects have been quantified using a modified temperature program, and corrected using a universal factor. A comparison of the experimental results with the predictions of various analytical solutions for isothermal solidification reveals that the moving interface solution can accurately predict the interface kinetics given accurate diffusion data. The DSC method has been used to quantify the process kinetics of isothermal solidification in a ternary alloy system, with results compared to a finite difference model for interface motion. The DSC results show a linear relationship between the interface position and the square root of the isothermal hold time. While the numerical simulations do not agree well with the experimental interface kinetics due to a lack of accurate thermodynamic data, the model does help develop an understanding of the isothermal solidification mechanics. Compositional shift at the solid/liquid interface has been measured experimentally and compared with predictions. The results show that the direction of tie-line shift can be predicted using numerical techniques. Furthermore, tie-line shift has been observed in the DSC results. This study has shown that DSC is an accurate and valuable tool in the development of parameters for processes employing isothermal solidification, such as TLP bonding.

L'assemblage tridimensionnel des circuits microélectroniques et leur utilisation dansdes conditions environnementales extrêmement sévères nécessitent ledéveloppement d’alternatives plus robustes pour les contacts électriques. Unetechnique prometteuse est la transformation des contacts de brasure conventionnelleen composés intermétalliques (IMC). Ce processus est appelé « Transient LiquidPhase Soldering » (TLPS).Dans ce contexte, des tests accélérés permettant la formation d’IMC parélectromigration et thermomigration ont été effectués sur des structures « Packageon Package ». L'objectif principal est le développement d'un modèle généralpermettant de décrire la formation des IMC dans les joints de brasure. Combiné avecune analyse par éléments finis ce modèle pourra être utilisé pour prédire la formationdes IMC dans les joints de brasure pour des structures et des profils de missiondifférents. Le modèle de formation des IMC pourra être utilisé pour optimiser unprocessus TLPS. / A further miniaturization of microelectronic components by three dimensionalpackaging, as well as the use of microelectronic devices under harsh environmentconditions, requires the development of more robust alternatives to the existing Snbased solder joints. One promising technique is the diffusion and migration driventransformation of conventional solder bumps into intermetallic compound (IMC)connections. The related process is called transient liquid phase soldering (TLPS).Against this background an investigation of the IMC formation under consideration ofelectromigration and thermomigration was performed. For the stress tests Packageon Package structures are used. The final result is a general model for the IMCformation in solder joints. Combined with a Finite Element Analysis (FEA) this modelis used to predict the IMC formation in solder joints for a broad range of boundaryconditions. In future the model of the IMC formation can be used to optimize a TLPSprocess.

Friction stir welding (FSW) of steel is often performed with an insert made of polycrystalline cubic boron nitride (PCBN). Specifically, MS80 is a grade of PCBN made by Smith MegaDiamond that has been optimized for the FSW process. The PCBN insert is attached to a tungsten carbide (WC) shank by a compression fitting. However, FSW tools manufactured by this method inevitably fail by fracture in the PCBN. Permanently bonding PCBN to WC would likely solve the fracturing problem and increase the life of PCBN FSW tools to be economically viable. Partial transient liquid phase (PTLP) bonding, a process used to join ceramics with thin metallic interlayers, was proposed as a method to permanently bond PCBN to WC. PTLP bonding is often performed using three layers of pure elements. On heating, the two thin outer interlayers melt and bond to the ceramics. Concurrently, these liquid layers diffuse into the thicker refractory core until solidification has occurred isothermally. A procedure was developed to reduce the number of possible three-layer PTLP bonding setups to a small set of ideal setups using logical filters. Steps in this filtering method include a database of all existing binary systems, sessile drop testing of 20 elements, and a routine that calculates maximum interlayer thicknesses. Results of sessile drop testing showed that the PCBN grade required for this research could only be bonded with an alloy of Ti, Cu, Mg, and Sb. Two PTLP bond setups were tested using this special coating on the PCBN, but a successful bond could not be achieved. However, a PTLP bond of WC to WC was successful and proved the usefulness of the filtering procedure for determining PTLP bond setups. This filtering procedure is then set forth in generalized terms that can be used to PTLP bond any material. Also, recommendations for future research to bond this grade of PCBN, or some other grade, to WC are presented.

L'objectif d'un avion plus électrique conduit à l'utilisation croissante de systèmes d'électronique y compris dans des zones de haute température. Les modules de puissance classiques doivent être adaptés à cet environnement: les composants en SiC sont commercialement disponibles mais l'environnement de la puce est à modifier. Cette thèse s'intéresse aux techniques d'attaches de puces basses température que sont le frittage d'argent et la brasure en phase liquide transitoire (TLPB) or-étain. Dans une première partie, les enjeux de l'électronique de puissance et plus particulièrement des applications haute température est donnée. Les mécanismes physique (mouillage, diffusion)qui régissent le frittage et le TLPB (Transient liquid Phase Bonding) sont ensuite décrits avec précision. La deuxième partie de cette thèse s'intéresse à la mise en oeuvre d'un protocole fiable d'attache de puce par frittage d'une nanopoudre d'argent commerciale. Une fois établie, la méthode a ensuite été optimisée pour différentes tailles de composants. La caractérisation de l'attache a été réalisée en shear-test et par des images en microscopie optique. La troisième et dernière partie de ce travail a pour objet la réalisation d'attaches de puces par TLPB or-étain. Ce chapitre traite de la mise en oeuvre expérimentale de la technique, depuis la métallisation des wafers jusqu'à la caractérisation des attaches en microscopie (optique et MEB). Ce travail de thèse est très expérimental car même si un protocole de mise en oeuvre existe (pour le frittage), il est indispensable de l'adapter aux conditions expérimentales pour l'optimiser. Ce travail a aussi mis en évidence certaines difficultés techniques de préparation des surfaces. / More electric aircaft projects lead to the increasing use of power electronic systems including in high temperature areas. Classical power modules must be adapted to this harsh environment: SiC devices are now commercially available but the packaging of the dies must be completely changed. This thesis focus on alternative die-backside attaches aand particularly on sintering and Transient Liquid Phase Bonding (TLPB) which are classified as Low Temperature Joining Techniques. In the first part, importance of power electronic systems for high temperature applications is given. Theoretical considerations about physical mechanisms (diffusion, wetting) involved in sintering and TLPB are described precisely. The purpose of the second part of this thesis is to establish a realiable protocole of die-attach using commercial silver nanopaste.the method has been optimized for different sizes of devices. Caracterization was provided using optical pictures and shear-test results. The third chapter of this work is about the realization of die-attaches using TLPB method. A description of surfaces preparation is given and diffusion results are discussed using SEM and optical pictures. This work is very experimental because sintering classical procedure must be adapted and optimized for each kind of devices. This thesis has clealy shown the difficulties for surfaces preparation.

<div> <div> <div> <p>Transient liquid phase sintering (TLPS) technologies are potential low-temperature solders for sustainable replacements of lead-based solders and high-temperature lead-free solders. Compared to solid-state sintering and lead-free solders, TLPS uses lower temperatures and is, thus, suitable for assembling temperature-sensitive components. TLPS is a non- equilibrium process and determining the kinetics is critical to the estimation of processing times needed for good joining. The tin-indium (Sn-In) system with a eutectic temperature of 119°C is being considered as the basis for a TLPS system when combined with tin. Most models of TLPS include interdiffusion, dissolution, isothermal solidification, and homogenization and are based on simple binary alloys without intermediate phases. The Sn-In system has two intermediate phases and thus the reaction kinetics require additional terms in the modeling. Differential Scanning Calorimetry (DSC) has been used to measure the response of Sn-In alloys during the transient liquid phase reaction. Preparation of tin indium alloys for microstructural analysis is challenging due to their very low hardness. This study uses freeze-fracturing of the tin indium alloys to obtain sections for microstructural analysis. The combination of DSC and microstructure analysis provides information on the reaction kinetics. It was observed that the solid/liquid reaction does not proceed as quickly as desired, that is, substantial liquid remains after annealing even though the overall composition is in the single-phase region in the phase diagram. </p> </div> </div> </div>