Hot isostatic pressing is now an accepted material processing technique for the consolidation of metal powders to near-net-shape components. This thesis examines the use of coatings as in-situ envelopes to overcome the problems associated with traditional containerisation of powder. The application of metallic coatings by physical vapour deposition, involving resistive and electron beam evaporation and ion plating, onto green powder metal compacts has been studied as a potential method for encapsulating powder metal products prior to hot isostatic pressing. The coating structures are discussed in terms of processing conditions and surface roughness influence. The most promising approach is a combined sinter-hot isostatic, pressing cycle, which utilises the formation of a transient liquid phase to defect-heal the coating during the sinter cycle prior to the application of pressure. The influence of particle size distribution on densification has also been studied. This included both monosized and bimodal powders. The results of this study has been incorporated into a modified Ashby model computer program and it is shown that the model results in a shift of the dominance of the mechanism fields and gives good correlation between the predicted and measured values of density.

Femtosecond laser interaction with dielectrics has unique characteristics for micromachining, notably non-thermal interaction with materials, precision and flexibility. The nature of this interaction is highly nonlinear due to multiphoton ionization, so the laser energy can be nonlinearly absorbed by the material, leading to permanent change in the material properties in a localized region of Mu-m3. This dissertation demonstrated the potential of these nonlinear interactions induced changes (index modification and ablation for machining) in the dielectrics and explored several practical applications. We studied femtosecond laser ablation of Poly-methayl methacrylate (PMMA) under single and multiple pulse irradiation regimes. We demonstrated that the onset of surface ablation in dielectric surface is associated with surface swelling, followed by material removal. Also, the shape of the ablation craters becomes polarization dependent with increasing fluence, except for circular polarization. The morphology of the damaged/ablated material was examined by optical and scanning electron microscopy. The dynamics of laser ablation of PMMA was simulated using a 2 dimensional Molecular Dynamics model and a 3 dimensional Finite Difference Time Domain model. The results from numerical simulations agreed well with experimental results presented in this thesis. We also demonstrated the formation of nano-pillar within the ablation crater when the surface of bulk-PMMA was irradiated by two femtosecond pulses at a certain delay with energies below single shot ablation threshold. With increasing fluence, the nano-pillar vanished and the structure within the ablation crater resembled volcanic eruption. At higher fluences we demonstrated nanoscale porosity in PMMA. For application, a novel in-line fiber micro-cantilever was fabricated in bend insensitive fiber, that provides details of in-line measurement of frequency and amplitude of vibration, and can be further extended to be used as chemical/bio and temperature sensors. By modifying the refractive index at random spacing within the single mode fiber core, a unique quasi-random micro-cavities fiber laser was fabricated, which exhibits comparable characteristics with a commercial fiber laser in terms of narrow linewidth and frequency stability.

Doctor of Philosophy / Department of Industrial & Manufacturing Systems Engineering / Shuting Lei / Lasers have been widely used as a manufacturing tool for material processing, such as drilling, cutting, welding and surface texturing. Compared to traditional manufacturing methods, laser-based material processing is high precision, can treat a wide range of materials, and has no tool wear. However, demanding manufacturing processes emerging from the needs of nano and 3D fabrication require the development of laser processing strategies that can address critical issues such as machining resolution, processing speed and product quality. This dissertation concerns the development of novel laser processing strategies based on spatial, temporal and spectral control of light-matter interaction. In the spatial domain, beam shaping is employed in ultrafast laser micro-processing. Zero-order Bessel beam, generated by an axicon, is used for selective removal of the back contact layer of thin film solar cells. Bessel beam’s propagation-invariance property gives rise to an extension of focal range by orders of magnitude compared to Gaussian beam, greatly increasing process tolerance to surface unevenness and positioning error. Together with the axicon, a spatial light modulator is subsequently used to modify the phase of laser beam and generate superpositions of high-order Bessel beam with high energy efficiency. With the superposed beam, processing speed can be increased significantly, and collateral damage resulting from the ring structures in the zero-order Bessel beam can be greatly suppressed. In the temporal domain, it is demonstrated that ionization in dielectric materials can be controlled with a pair of ultraviolet and infrared pulses. With the assistance of the long-wavelength infrared pulse, nano-scale features are achieved using only a small fraction of threshold energy for the short-wavelength pulse. Computer simulation based on the rate equation model is conducted and found to be in good agreement with experimental results. This study paves the way for future adoption of short-wavelength laser sources, for example in the extreme ultraviolet range, for direct laser nano-fabrication with below-threshold pulse energy. In the spectral domain, a short-wavelength infrared laser is used to generate modification in the bulk of silicon wafers, in an attempt to develop 3D fabrication capabilities in semiconductors. Issues such as spherical aberration correction and examination procedure are addressed. Permanent modification is generated inside silicon by tightly focusing and continuously scanning the laser beam inside the samples, without introducing surface damage. The effect of laser pulse energy and polarization is also investigated. These results demonstrate the potential of controlling laser processing in multiple dimensions for manufacturing purposes, and point to a future when laser can be used as naturally and efficiently as mechanical tools used today, but is targeted at more challenging problems.

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No description available.

Materials processing using microwave radiation is emerging as a novel and innovative technology that has proven useful in a number of applications. It has various advantages over conventional processing, such as; time and energy saving, very rapid heating rates, considerably reduced processing time and temperature, fine microstructures and improved mechanical properties, better product performance, etc. Microwave irradiation has shown great potential for the processing of different semiconductor materials and inorganic solids for various advanced electronic and optoelectronic devices such as solar cells, batteries, supercapacitors, fuel cells etc. This work intends to investigate the effect of microwave radiation on various semiconductor materials and inorganic solids, in particular the changes in their chemical, physical and photoelectrochemical properties after microwave treatment. Microwaves have been used as an alternative method to conventional thermal annealing for post annealing of widely used semiconductors (TiO2, ZnO nanorods), battery materials (lithium aluminium titanium phosphates), and synthesis of materials (ZnO, Ti0.97Pd0.03O1.97). It is found that, in contrast to conventional thermal annealing, microwave treatment of such materials improves the crystallinity without any structural changes by preserving their nanostructure due to the difference in the heating mechanism (volumetric heating). The results demonstrate that microwave processing is a promising alternative method to the traditional conventional sintering for materials processing for advanced electronic and optoelectronic devices. Also the microwave annealing method offers energy savings of up to ~75%, which would make it highly desirable for industrial scale up.

The quality of parts fabricated using Laser Solid Freeform Fabrication (LSFF) is highly dependent on the physical phenomena and operating parameters which govern the process. For instance, the thermal stress patterns and intensity, induced throughout the process domain due to the layer-by-layer material deposition and the temperature distribution characteristics, contribute significantly to potential delamination and crack formation across the fabricated part. In this research, some of the main features as well as drawbacks of this technique are studied through a multi-physics analysis of the process. For this purpose, a coupled time-dependent 3D model is developed with which the geometry of the deposited material as well as temperature and thermal stress fields across the process domain can be predicted. In the proposed approach, coupled thermal and stress domains are numerically obtained assuming a decoupled interaction between the laser beam and powder stream. To predict the geometry of the deposited material, once the melt pool boundary is obtained, the process domain is discretized in a cross-sectional fashion based on the powder feed rate, elapsed time, and intersection of the melt pool and powder stream projected on the substrate. Layers of additive material are then added onto the non-planar domain. The main process parameters affected by a multilayer deposition due to the formation of non-planar surfaces, such as powder catchment, are incorporated into the modelling approach to enhance the accuracy of the results. To demonstrate the proposed algorithm and to study the main features of the process, a four-layer thin wall of AISI 304L steel on a substrate of the same material is numerically and experimentally fabricated. The numerical analyses along with the experimental results are then used to investigate the correlation between the temperature-thermal stress fields and crack formation across the fabricated parts. The trend of the results reveals that by preheating the substrate prior to the fabrication process, it is possible to substantially reduce the formed micro-cracks. To demonstrate the feasibility of preheating on the reduction of micro-cracks, several simulations and experiments are performed in which a crack-free result is obtained, with a 22 per cent reduction in thermal stresses when the substrate is preheated to 800 K. The numerical and experimental results are also used to study the circumstances of the microstructural formation during the fabrication process. To conclude this research, the developed modelling approach is further extended to briefly discuss the effects of the path patterns and the main operating parameters on the outcomes of the process. The effects of the material properties and their variations on the temperature distributions and thermal stress fields are studied by fabrication of a thin wall of two Stellite 6 layers and two Ti layers on a stainless steel substrate.

The quality of parts fabricated using Laser Solid Freeform Fabrication (LSFF) is highly dependent on the physical phenomena and operating parameters which govern the process. For instance, the thermal stress patterns and intensity, induced throughout the process domain due to the layer-by-layer material deposition and the temperature distribution characteristics, contribute significantly to potential delamination and crack formation across the fabricated part. In this research, some of the main features as well as drawbacks of this technique are studied through a multi-physics analysis of the process. For this purpose, a coupled time-dependent 3D model is developed with which the geometry of the deposited material as well as temperature and thermal stress fields across the process domain can be predicted. In the proposed approach, coupled thermal and stress domains are numerically obtained assuming a decoupled interaction between the laser beam and powder stream. To predict the geometry of the deposited material, once the melt pool boundary is obtained, the process domain is discretized in a cross-sectional fashion based on the powder feed rate, elapsed time, and intersection of the melt pool and powder stream projected on the substrate. Layers of additive material are then added onto the non-planar domain. The main process parameters affected by a multilayer deposition due to the formation of non-planar surfaces, such as powder catchment, are incorporated into the modelling approach to enhance the accuracy of the results. To demonstrate the proposed algorithm and to study the main features of the process, a four-layer thin wall of AISI 304L steel on a substrate of the same material is numerically and experimentally fabricated. The numerical analyses along with the experimental results are then used to investigate the correlation between the temperature-thermal stress fields and crack formation across the fabricated parts. The trend of the results reveals that by preheating the substrate prior to the fabrication process, it is possible to substantially reduce the formed micro-cracks. To demonstrate the feasibility of preheating on the reduction of micro-cracks, several simulations and experiments are performed in which a crack-free result is obtained, with a 22 per cent reduction in thermal stresses when the substrate is preheated to 800 K. The numerical and experimental results are also used to study the circumstances of the microstructural formation during the fabrication process. To conclude this research, the developed modelling approach is further extended to briefly discuss the effects of the path patterns and the main operating parameters on the outcomes of the process. The effects of the material properties and their variations on the temperature distributions and thermal stress fields are studied by fabrication of a thin wall of two Stellite 6 layers and two Ti layers on a stainless steel substrate.

L'intérêt porté au développement de matériaux thermoélectriques est grandissant car ils permettent de créer des sources d'énergie renouvelable, dites « vertes », ce qui s'inscrit pleinement dans la stratégie de lutte contre le réchauffement climatique. A ce jour le rendement de tels systèmes reste faible, le coût de développement élevé, et les plages de températures d'utilisation sont limitées. Dans ces travaux de thèse différentes pistes sont explorées pour développer des matériaux innovants à base de chalcogènes, principalement le tellure. Les principaux résultats portent sur les points suivants. (i) Une étude par spectroscopies couplée à des calculs théoriques a permis de mieux comprendre les phénomènes de conduction dans les verres du système Cu-As-Te. (ii) La recristallisation complète de verres de formulation Ge20Te77Se3 dopés a été réalisée pour pousser à son terme la logique dite du Phonon Glass Electron Crystal (PGEC).(iii) Différents modes de synthèses ont été mis en œuvre pour suivre les propriétés thermoélectriques de matériaux de formulation CuPb18SbTe20 (frittage, SPS, flash-SPS, hybrid flash-SPS). (iv) Accroissement de 170% des performances d'alliage du système Pb-Sb-Te en générant des vacances de sites (composés non-stœchiométriques). (v) Le suivi des conséquences du dopage de GeTe par un seul élément a montré la nécessité d'un co-dopage pour simultanément accroître la conductivité électronique et le Seebeck. (vi) Le co-dopage In-Bi de GeTe a permis de créer des niveaux résonants (In) et d'accroitre la diffusion thermique (Bi). (vii) Enfin, le résultat le plus remarquable porte sur le co-dopage Ga-Sb de GeTe qui permet d'effectuer de l'ingénierie de structure de bandes. Couplé à une synthèse par hybrid flash SPS ces matériaux prometteurs permettent d'obtenir un zT 2 sur une large gamme de température (600–773 K). / With the performance of direct conversion between thermal and electrical energy, thermoelectric materials, which are crucial in the renewable energy conversion roadmap, provide an alternative for power generation and refrigeration to solve the global energy crisis. But the low efficiency of the current materials, their usual costs, availability, and limited working temperatures, drastically constrain their application. Hence, the search for new and more efficient thermoelectric materials is one of the most dynamic objectives of this thesis. The key milestones achieved from this thesis work includes: (i) elucidating the mechanism for hole conductivity in Cu-As-Te glasses by X-ray absorption spectroscopy and quantum simulations; (ii) formulating a novel approach to achieve phonon-glass electron-crystal mechanism by crystallizing the Ge20Te77Se3 glasses by excess doping with metals or semi-metals (glass-ceramics); (iii) demonstrating the effect of processing route on the thermoelectric performance of CuPb18SbTe20 and highlighting the advantage of hybrid-flash spark plasma sintering technique, i.e., better optimization of electrical and thermal transport properties and achieving multi-scale hierarchical architectures; (iv) improving the thermoelectric performance of Pb-Sb-Te alloys (enhancement by 170%) by tuning their cation vacancies (Pb deficiencies); (v) understating the impact of doping just a group-11 coinage metal, or group-13 element on GeTe solid-state solution and recapitulating the need for pair substitution; (vi) substantially enhancing the average zT of In-Bi codoped GeTe; (vii) achieving a remarkably high and stable zT of close to 2 over a wide temperature range (600 – 773 K) by manipulating the electronic bands in Ga-Sb codoped GeTe, which has been processed by hybrid flash-spark plasma sintering, thus making it a serious candidate for energy harvesting systems.

I dagsläget använder sig Plastic Produkter AB sig av termoformningsmaskiner för hantering av halvfabrikat av termoplaster, en maskin som de tillverkat och även sålt vidare till olika sorters kunder. Ursprungsmaskinen tillverkades i ett simpelt utförande endast för att klara grund behovet att bocka olika arbetsstycken. Eftersom marknaden samt utvecklingen av olika metoder sedan dess har gått framåt finns ett intresse av att vidareutveckla nuvarande termoformningsmaskin för halvfabrikat av termoplaster. I nuvarande version krävs det att användaren kan ställa om maskinen manuellt mellan olika typer av operationer som underlättar användningen av maskinen för användaren. Uppgiften i detta projekt har därför varit att vidareutveckla termoformningsmaskinen genom att optimera dess process men även automatisera olika typer av regleringar gällande avståndsmätning mellan viktiga delar av termoformningsmaskinen. För att komma fram till ett tillfredställande resultat har olika undersökningar skett, samt fakta tagits fram till grund för utvecklingen av de olika koncept som kan bidra till en konkurrenskraftig maskin. Ur dessa har det mest lovande konceptet tagits fram genom olika typer av matriser samt diskussioner med användare och företagets representant. Resultatet är en vidareutveckling genom en modifiering av nuvarande termoformningsmaskin genom tre stycken olika koncept. I dessa ligger stort fokus att uppgradera termoformningsmaskinen för att underlätta för användaren och minska de olika manuella moment som i dagens läge krävs för vissa typer av omställningar och även förbättra det resultat som termoformningsmaskinen ger på ett arbetsstycke. / In the current situation Plastic Produkter AB uses thermoforming machines for handling semi-finished products of thermoplastics. A machine they manufactured and also sold to different kinds of customers. The original machine was manufactured in a simple design only to cope with the need to bend different work pieces. Since the market and the development of different methods have developed, there is an interest in further developing the current thermoforming machine for semimanufactured thermoplastics. In the current version the user is required to manually switch the machine between different types of operations, certain efficiency and improvement is required, which facilitates the use of the machine for the user. The task of this project has therefor been to further develop the thermoforming machine by optimizing its process, but also automating different types of distance measurement regulations between key parts of the thermoforming machine. In order to arrive at a satisfactory result, various investigations have taken place, as well as the facts underlying the development of the different concepts that can contribute to a competitive machine. From these, the most promising concept has been developed through different types of matrices as well as discussions with users and company representatives. The result was a further development through a modification of the current thermoforming machine through three different concepts. In these concepts, great focus is on upgrading the thermoforming machine to facilitate the user and reduce the different manual moments required at present for certain types of switches and also to improve the performance of the thermoforming machine from the work piece.