No / The transient liquid phase (TLP) bonding of Ti-6Al-4V alloy to a Mg-AZ31 alloy was performed using an electrodeposited Ni coating containing a dispersion of Ni and Cu nanoparticles. Bond formation was attributed to two mechanisms; first, solid-state diffusion of Ni and Mg, followed by liquid eutectic formation at the Mg-AZ31 interface. Second, the solid-state diffusion of Ni and Ti at the Ti-6Al-4V interface resulted in a metallurgical joint. The joint interface was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction analysis. Microhardness and shear strength tests were used to investigate the mechanical properties of the bonds. The use of Cu nanoparticles as a dispersion produced the maximum joint shear strength of 69 MPa. This shear strength value corresponded to a 15 % enhancement in joint strength compared to TLP bonds made without the use of nanoparticles dispersion. / The authors would like to acknowledge The German Jordanian University (GJU), and NSERC Canada for the financial support for this research.

This research seeks to increase the applicable range and sensitivity of Triple Langmuir Probes (TLPs) and Retarding Potential Analyzers (RPAs) in the characterization of sub-centimeter scale, unsteady plasmas found in micropropulsion and other non-propulsive applications. The validation of these plasma diagnostics is accomplished by their implementation in the plume of a Micro Liquid-fed Pulsed Thruster (MiLiPulT) prototype developed and MEMS fabricated by the Johns Hopkins University Applied Physics Laboratory. A current-mode TLP (CM-TLP) theory of operation for the thin-sheath and the transitional regimes is expanded to include the Orbital Motion Limited regime applicable to low density plasmas. An optimized CM-TLP bias circuit employing operational amplifiers in both a differential amplifier configuration as well as a voltage follower configuration has been developed to adequately amplify current signals in instances where traditional current measuring techniques are no longer valid. This research also encompasses novel sub-microampere signal amplification in the presence of substantial common-mode noise as well as several a priori electromagnetic interference elimination and filtering techniques. The CM-TLP wires used in the experiments were designed with a radius of 37.5 micron and a length of 5 mm. Measurements were taken in the plume of the MiLiPulT at 2.0 cm, 6.0 cm and 10.0 cm downstream of the exit using a linear translation stage. Reduced electron temperature and electron number density profiles for a set of filtered CM-TLP raw currents are presented. The results indicate increased accuracy due to successful amplification of CM-TLP current signals at the risk of op-amp saturation due to inherent electrical noise of the plasma source. This research also includes the experimental validation of two new and distinct collimating RPA design types. Specifically, these design improvements include a 406 micron diameter single channel bore and a multi-channel plate (MCP) consisting of sixty-four 2 micron diameter bores, respectively. Both of these collimators relax the Debye length constraints within the electrode series and increase the instrument's range while minimizing the presence of space charge limitations. The single channel needle also has the added advantage of providing a relatively small cross-section to the incident plasma, thus minimizing pressure gradients and shock effects inherent to bulkier instrumentation. Experimental results obtained in the plume of the MiLiPulT are benchmarked against those of a traditional gridded RPA (having a 650 micron grid wire gap) and are reduced using an iterative fuzzy logic algorithm. Modifications to the classical RPA current collection theory include a thorough treatment of geometrical flux limitations due to an electrically floating cylindrical channel of high diameter to length aspect ratio. The differences between true and effective RPA collimating channel transparencies in the presence of a Maxwellian plasma are also addressed.

The problem of inadequate measurement techniques for quantifying the isothermal solidification process during transient liquid phase sintering (TLPS) in binary isomorphous systems such as Ni-Cu, and the resulting uncertainty regarding the solidification mechanism and its sensitivity to important process parameters, has been investigated. A unique combination of differential scanning calorimetry (DSC), neutron diffraction (ND), and metallographic techniques has enabled the quantitative characterization of important TLPS stages (i.e., solid-state sintering, melting and dissolution, isothermal solidification, and homogenization) as well as verifying the re-melt behaviour of post-sintered specimens and measuring variable melting point (VMP) properties. This has resulted in the advancement of the fundamental understanding of liquid formation and its removal mechanism during isothermal, or diffusional, solidification. The Ni-Cu system was chosen for experimentation due to its commercial relevance as a braze filler material and also because it is an ideal model system (due to its isomorphous character) that is not well understood on a quantitative or phenomenological basis. Samples consisted of elemental Ni and Cu powder mixtures of varying particle size and composition. In DSC experiments, the progress of isothermal solidification was determined by measuring the enthalpy of melting and solidification after isothermal hold periods of varying length and comparing these to the measured enthalpy of pure Cu. The low melting enthalpies measured for all Ni/Cu mixtures heated just past the Cu melting point (1090°C) indicate that solid-state sintering and interdiffusion during heat-up significantly suppress initial liquid formation and densification from the wetting liquid. For samples heated well past the Cu melting point (1140°C), Ni dissolution causes increased initial liquid fractions and densification. It was found that significantly more time was required for complete liquid removal at 1140°C vs. 1090°C. This is attributed to the observed increase in initial liquid fractions formed at higher processing temperatures due to the dissolution of Ni. This effectively counteracts the increased diffusivities at these temperatures, and thus more time is required to completely remove the increased liquid content. TLP mixtures sintered at 1140°C using three different particle sizes revealed that fine base metal Ni particles cause high degrees of solid-state interdiffusion during heat-up, small initial liquid fractions, and accelerated liquid removal rates due to high surface area/volume ratios. A diffusion-based analytical model was developed to account for these effects (i.e., particle size, temperature, solid-state sintering, and dissolution). Comparison with experimental DSC results reveals that this model can accurately predict liquid removal given accurate diffusivities. Metallographic analysis of post-sintered DSC specimens via SEM and EDS indicates that isothermal liquid solidification leaves behind Ni-rich cores surrounded by Cu-rich matrix regions having compositions given by the Ni-Cu phase diagram solidus (CS) at a selected isothermal processing temperature (TP). ND experiments were used to investigate the melting event and interdiffusion during the isothermal hold segment by analyzing the evolution of the {200} FCC peaks of Ni and Cu. ND patterns were collected in situ at 1 minute intervals during prolonged sintering cycles for larger powder specimens. The Cu melting event was characterized by an abrupt decrease in Cu peak intensity at 1085°C as well as a shift towards higher 2 angles corresponding to lower Cu contents. This shifted residual peak (hereafter referred to as the CS peak) originates from regions of the specimen having compositions near solidus at TP. Immediately following the melting event, the evolution of ND patterns shows that these CS peaks grow rapidly, indicating the isothermal growth of a Cu-rich phase. These in situ findings confirmed the metallographic and DSC data and indicated that isothermal solidification of the liquid phase proceeds via the growth of a solute-rich solid solution layer surrounding the Ni particles. This occurs by the transient progression of the solid/liquid interface at compositions given by the liquidus and solidus (CS/CL). During sintering, diffraction intensities gradually increased at intermediate 2 angles between previous Ni and Cu peaks. ND patterns gradually evolved from initially having a broad double-peak profile to a sharper single-peak profile due to increased Ni-Cu interdiffusion. The 2position and width of the post-sintered peaks indicated very homogeneous sintered alloys. Metallographic analysis of post-sintered specimens having undergone prolonged sintering and homogenization revealed extensive Kirkendall pore formation from unequal diffusivities (DCu > DNi). In this study, the unique combination of diffusion-based modelling as well as DSC, ND, and supporting metallographic analysis has enabled the identification of characteristic sintering behaviour, important process parameters, and processing windows for TLPS in Ni-Cu systems. Quantitative and in situ information of this nature is absent in the previous TLPS literature.

The problem of inadequate measurement techniques for quantifying the isothermal solidification process during transient liquid phase sintering (TLPS) in binary isomorphous systems such as Ni-Cu, and the resulting uncertainty regarding the solidification mechanism and its sensitivity to important process parameters, has been investigated. A unique combination of differential scanning calorimetry (DSC), neutron diffraction (ND), and metallographic techniques has enabled the quantitative characterization of important TLPS stages (i.e., solid-state sintering, melting and dissolution, isothermal solidification, and homogenization) as well as verifying the re-melt behaviour of post-sintered specimens and measuring variable melting point (VMP) properties. This has resulted in the advancement of the fundamental understanding of liquid formation and its removal mechanism during isothermal, or diffusional, solidification. The Ni-Cu system was chosen for experimentation due to its commercial relevance as a braze filler material and also because it is an ideal model system (due to its isomorphous character) that is not well understood on a quantitative or phenomenological basis. Samples consisted of elemental Ni and Cu powder mixtures of varying particle size and composition. In DSC experiments, the progress of isothermal solidification was determined by measuring the enthalpy of melting and solidification after isothermal hold periods of varying length and comparing these to the measured enthalpy of pure Cu. The low melting enthalpies measured for all Ni/Cu mixtures heated just past the Cu melting point (1090°C) indicate that solid-state sintering and interdiffusion during heat-up significantly suppress initial liquid formation and densification from the wetting liquid. For samples heated well past the Cu melting point (1140°C), Ni dissolution causes increased initial liquid fractions and densification. It was found that significantly more time was required for complete liquid removal at 1140°C vs. 1090°C. This is attributed to the observed increase in initial liquid fractions formed at higher processing temperatures due to the dissolution of Ni. This effectively counteracts the increased diffusivities at these temperatures, and thus more time is required to completely remove the increased liquid content. TLP mixtures sintered at 1140°C using three different particle sizes revealed that fine base metal Ni particles cause high degrees of solid-state interdiffusion during heat-up, small initial liquid fractions, and accelerated liquid removal rates due to high surface area/volume ratios. A diffusion-based analytical model was developed to account for these effects (i.e., particle size, temperature, solid-state sintering, and dissolution). Comparison with experimental DSC results reveals that this model can accurately predict liquid removal given accurate diffusivities. Metallographic analysis of post-sintered DSC specimens via SEM and EDS indicates that isothermal liquid solidification leaves behind Ni-rich cores surrounded by Cu-rich matrix regions having compositions given by the Ni-Cu phase diagram solidus (CS) at a selected isothermal processing temperature (TP). ND experiments were used to investigate the melting event and interdiffusion during the isothermal hold segment by analyzing the evolution of the {200} FCC peaks of Ni and Cu. ND patterns were collected in situ at 1 minute intervals during prolonged sintering cycles for larger powder specimens. The Cu melting event was characterized by an abrupt decrease in Cu peak intensity at 1085°C as well as a shift towards higher 2 angles corresponding to lower Cu contents. This shifted residual peak (hereafter referred to as the CS peak) originates from regions of the specimen having compositions near solidus at TP. Immediately following the melting event, the evolution of ND patterns shows that these CS peaks grow rapidly, indicating the isothermal growth of a Cu-rich phase. These in situ findings confirmed the metallographic and DSC data and indicated that isothermal solidification of the liquid phase proceeds via the growth of a solute-rich solid solution layer surrounding the Ni particles. This occurs by the transient progression of the solid/liquid interface at compositions given by the liquidus and solidus (CS/CL). During sintering, diffraction intensities gradually increased at intermediate 2 angles between previous Ni and Cu peaks. ND patterns gradually evolved from initially having a broad double-peak profile to a sharper single-peak profile due to increased Ni-Cu interdiffusion. The 2position and width of the post-sintered peaks indicated very homogeneous sintered alloys. Metallographic analysis of post-sintered specimens having undergone prolonged sintering and homogenization revealed extensive Kirkendall pore formation from unequal diffusivities (DCu > DNi). In this study, the unique combination of diffusion-based modelling as well as DSC, ND, and supporting metallographic analysis has enabled the identification of characteristic sintering behaviour, important process parameters, and processing windows for TLPS in Ni-Cu systems. Quantitative and in situ information of this nature is absent in the previous TLPS literature.

No / The transient liquid phase bonding process has long been dealt with as a pure diffusion process at the joint interface, that is, as a mass phenomenon. In spite of the advances in the application of this technique to bond complex engineering alloys, the available models have failed to incorporate the effect of surface phenomena on the joining process. In this work, a new reaction–controlled diffusion formulation model is proposed, and the observation of experimental results of joining Al6061 alloy using thin single (50, 100 micron) and double Cu foils is recorded. This work directly unveils the unique role played by surface reaction–controlled diffusion rather than purely mass diffusion bonding process. Our experimental and modeling results reveal a conceptually new understanding that may well explain the joint formation in TLP bonding process.

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.

Grâce à l'augmentation continue des performances des circuits intégrés, l'électronique s'est largement développée dans la plupart des secteurs d'activité et tout particulièrement dans les systèmes embarqués. Ces systèmes doivent répondre à des contraintes de fiabilité sévères pour résister à des agressions issues de phénomènes transitoires variés, comme les décharges électrostatiques (ESD). À l'heure actuelle, l'impact de ces agressions sur le taux de retours clients des circuits intégrés est de 40 à 50 %. Pour améliorer l'immunité du système, et réduire ainsi les coûts de production et de suivi des produits, il devient nécessaire de prendre en compte ces perturbations dès la conception et d'avoir une approche globale de protection. Dans le cadre de ces travaux de thèse, nous avons développé une méthodologie de simulation, des modèles et les techniques de caractérisation associées afin d'évaluer l'impact d'un stress ESD en tous points d'une carte électronique en fonction des caractéristiques de chaque composant et du placement/routage. L'approche de modèlisation choisie s'appuie sur les outils informatiques de conception fonctionnelle des circuits et cartes et utilise le langage VHDL-AMS dont la certification IEEE en fait un standard industriel. Pour la caractérisation, l'originalité concerne l'utilisation d'un banc de test en impulsions de type Very Fast-TLP, couplé à différentes méthodes d'injection, qui permet à la fois, l'extraction des paramètres pour les modèles et d'observer la réponse du circuit intégré agressé sur la carte. Le résultat majeur de cette étude est la possibilité de simuler la réponse d'une carte électronique à une agression ESD (ex : ESD de type IEC) depuis son impact jusqu'au niveau de toute entrée/sortie des composants de la carte. L'approche est validée sur un circuit test simple mais aussi sur une application plus complexe à base d'un microcontrôleur. Elle permet de s'assurer que chaque composant est adéquat en termes de robustesse et de détecter des couplages indésirés.

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