Synthesis and Mechanical Properties of Metallic Multilayers

Compositionally modulated alloys and artificial superlattices are thin-layered structures where the layer thickness is on the order of a few 10s of lattice constants. These alloys have been shown to be unusually strong. Their overall thickness can be very large, in this study we have grown these to a thickness of 45 µm by 2.5 cm, in diameter, much greater than the average. We posit the reasons for this strength are that, during deformation, glissile dislocations are pinned at layer boundaries, the presence of image forces, and the formation of Lomer-Cottrell and Hirth dislocation locks. In this thesis we examine the fundamental reasons why layered alloys show such as high yield stress and compare our experimental data with our strength model using compositionally modulated copper-nickel as an example. We combine experimental synthesis with the molecular dynamics modelling using LAMMPS to compare this data with first principle modelling. LAMMPS shows dislocations pinning at alternate boundaries, consistent with literature observations. The consequences of this work bears directly on the fields of electrical contacts, sliding wear, and even enhancement of bulk materials strength. We have found that Cu-Ni compositionally modulated alloys can exhibit a hardness of over 500 Hv which corresponds to breaking stresses over 1.5 GPa. We have not observed a significant systematic modulus enhancement. We show that is it possible to produce these compositionally modulated alloys directly on copper coated silicon by electrodeposition through a mask to yield strong materials that can have consequences for new kinds of technological advances in integrated circuit processing that can be integrated into existing manufacturing methods. Because electrochemical deposition is widely used in the field of contacts, these results can have almost immediate practical application in this field. Electrodeposition is also an ambient temperature process, so interfaces can be made very compositionally sharp allowing components mounted on adjacent circuits to remain thermally undamaged. Using this process, it is possible to electrochemically place extremely strong metals anywhere on conductive substrate at essentially ambient temperature

Electrodeposited epitaxial cobalt oxides and copper metal

Electrochemical deposition methods are presented for the deposition of Co(OH)2 and Cu metal. Paper I shows the deposition of β-Co(OH)2 on Ti through electrochemical reduction of [Co(en)3]3+ to [Co(en)3]2+ in 2M NaOH. The catalytic properties of the deposited Co(OH)2 towards water oxidation is found comparable to Co3O4, with the surface of the Co(OH)2 converting to CoOOH during the reaction. Paper II gives the conditions suitable for epitaxial growth of Co(OH)2 on Au(100), Au(110), and Au(111) following the same reduction mechanism as described in Paper I. The epitaxial films are converted to CoOOH electrochemically or to Co3O4 thermally, each retaining epitaxy to the Au substrate even through drastic structure changes. Epitaxial CoOOH and Co3O4 develop pores and cracks during conversion leading to an increase in the surface area with respect to the initially deposited Co(OH)2 film. Paper III gives conditions for the deposition of epitaxial Cu(100) films on Si(100). This represents only the second metal in the literature to be electrodeposited epitaxially on Si. Cu films are deposited from a dilute pH 3 CuSO4 electrolyte using a two potential step nucleation and growth method. Nucleation occurs at -1.5 VAg/AgCl, a potential negative of the Si oxidation potential, keeping the Si surface reduced and enabling epitaxial nuclei to form. The nuclei are grown at -0.5 VAg/AgCl, a potential positive of the Si oxidation potential, resulting in the concurrent undergrowth of SiOx between the Cu film and Si substrate. Chemical etching of the SiOx with 5% HF allows the Cu film to be separated from the Si substrate yielding a freestanding nanometer thick Cu single-crystal-like foil. Epitaxial Cu films and foils are potentially useful ordered substrates for integrated circuits or flexible electronics --Abstract, page iv

Understanding and predicting metallic whisker growth and its effects on reliability : LDRD final report.

Tin (Sn) whiskers are conductive Sn filaments that grow from Sn-plated surfaces, such as surface finishes on electronic packages. The phenomenon of Sn whiskering has become a concern in recent years due to requirements for lead (Pb)-free soldering and surface finishes in commercial electronics. Pure Sn finishes are more prone to whisker growth than their Sn-Pb counterparts and high profile failures due to whisker formation (causing short circuits) in space applications have been documented. At Sandia, Sn whiskers are of interest due to increased use of Pb-free commercial off-the-shelf (COTS) parts and possible future requirements for Pb-free solders and surface finishes in high-reliability microelectronics. Lead-free solders and surface finishes are currently being used or considered for several Sandia applications. Despite the long history of Sn whisker research and the recently renewed interest in this topic, a comprehensive understanding of whisker growth remains elusive. This report describes recent research on characterization of Sn whiskers with the aim of understanding the underlying whisker growth mechanism(s). The report is divided into four sections and an Appendix. In Section 1, the Sn plating process is summarized. Specifically, the Sn plating parameters that were successful in producing samples with whiskers will be reviewed. In Section 2, the scanning electron microscopy (SEM) of Sn whiskers and time-lapse SEM studies of whisker growth will be discussed. This discussion includes the characterization of straight as well as kinked whiskers. In Section 3, a detailed discussion is given of SEM/EBSD (electron backscatter diffraction) techniques developed to determine the crystallography of Sn whiskers. In Section 4, these SEM/EBSD methods are employed to determine the crystallography of Sn whiskers, with a statistically significant number of whiskers analyzed. This is the largest study of Sn whisker crystallography ever reported. This section includes a review of previous literature on Sn whisker crystallography. The overall texture of the Sn films was also analyzed by EBSD. Finally, a short Appendix is included at the end of this report, in which the X-Ray diffraction (XRD) results are discussed and compared to the EBSD analyses of the overall textures of the Sn films. Sections 2, 3, and 4 have been or will be submitted as stand-alone papers in peer-reviewed technical journals. A bibliography of recent Sandia Sn whisker publications and presentations is included at the end of the report

Understanding the Mechanical Behaviors of Lithium-Based Battery Anodes─Silicon and Lithium Metal

abstract: This dissertation will investigate two of the most promising high-capacity anode materials for lithium-based batteries: silicon (Si) and metal lithium (Li). It will focus on studying the mechanical behaviors of the two materials during charge and discharge and understanding how these mechanical behaviors may affect their electrochemical performance. In the first part, amorphous Si anode will be studied. Despite many existing studies on silicon (Si) anodes for lithium ion batteries (LIBs), many essential questions still exist on compound formation, composition, and properties. Here it is shown that some previously accepted findings do not truthfully reflect the actual lithiation mechanisms in realistic battery configurations. Furthermore the correlation between structure and mechanical properties in these materials has not been properly established. Here, a rigorous and thorough study is performed to comprehensively understand the electrochemical reaction mechanisms of amorphous-Si (a-Si) in a realistic LIB configuration. In-depth microstructural characterization was performed and correlations were established between Li-Si composition, volumetric expansion, and modulus/hardness. It is found that the lithiation process of a-Si in a real battery setup is a single-phase reaction rather than the accepted two-phase reaction obtained from in-situ TEM experiments. The findings in this dissertation establish a reference to quantitatively explain many key metrics for lithiated a Si as anodes in real LIBs, and can be used to rationally design a-Si based high-performance LIBs guided by high-fidelity modeling and simulations. In the second part, Li metal anode will be investigated. Problems related to dendrite growth on lithium metal anodes such as capacity loss and short circuit present major barriers to the next-generation high-energy-density batteries. The development of successful mitigation strategies is impeded by the incomplete understanding of the Li dendrite growth mechanisms. Here the enabling role of plating residual stress in dendrite initiation through novel experiments of Li electrodeposition on soft substrates is confirmed, and the observations is explained with a stress-driven dendrite growth model. Dendrite growth is mitigated on such soft substrates through surface-wrinkling-induced stress relaxation in deposited Li film. It is demonstrated that this new dendrite mitigation mechanism can be utilized synergistically with other existing approaches in the form of three-dimensional (3D) soft scaffolds for Li plating, which achieves superior coulombic efficiency over conventional hard copper current collectors under large current density.Dissertation/ThesisDoctoral Dissertation Mechanical Engineering 201

Critical analysis of accumulated experimental data on filament-reinforced metal matric composites

Data analysis on filament reinforced metal matrix composite

Grafeenil põhinevate struktuuride kompleksne nanoskoopiline karakteriseerimine

Väitekirja elektrooniline versioon ei sisalda publikatsiooneAntud töö raames valmistati ja karakteriseeriti puhtal ja funktsionaliseeritud kujul mõne- ja mitmekihilisel grafeenil põhinevaid struktuure, kasutades erinevaid spektroskoopia ja kõrglahutusmikroskoopia meetodeid. Selleks juurutati mõnekihilise ja mitmekihilise grafeeni süntees keemilise aurufaassadestamise meetodil nikkelkatalüsaatoril ning valmistatud grafeenikihtide omadusi võrreldi grafiidi mikromehhaanilise lõhestamise teel või keemilise aurufaasist sadestamise meetodil saadud ühekihilise grafeeni omadustega. Näidati grafeeni kasvu sõltuvust nikkelaluse paksusest ja kristalliitide orientatsioonist. Leiti, et nikli pinnal sünteesitud mitmekihilise grafeeni kiles esinevad monokihtide erinevate pakmetega alad. Seejuures, kui pöördenurk grafeenikihtide vahel oli suurem kui kriitiline nurk (~13 kraadi), siis ilmnesid mitmekihilise grafeeni ramanhajumise spektris monokihilise grafeeni spektrile iseloomulikud tunnused. Samuti näidati, et grafeeni kasvuga kaasnevad polükristalliliste nikkelaluste pinna morfoloogia muutused. Edasi testiti Ni-alusel sünteesitud mitmekihilise grafeeni elektrokeemilisi omadusi ning uuriti selle funktsionaliseerimise võimalust ilma grafeeni metallaluselt eemaldamata. Uuringutest selgus, et nikkelkatalüsaatoril keemilise aurufaasist sadestamise meetodil kasvatatud mitmekihilist grafeeni saab kasutada elektrokeemiliselt passiivse alusmaterjalina elektrokatalüütiliselt aktiivsete materjalide uurimiseks. Kasutades arüüldiasooniumsoolade elektrokeemilist redutseerimist, saab sünteesitud mitmekihilise grafeeni pinda modifitseerida arüülrühmadega, mis võimaldab laiendada sünteesitud grafeeni kasutamist. Lisaks uuriti transistorstruktuuri paisudielektrikkile kasvatamise võimalust grafeeni pinnale aatomkihtsadestamise meetodi abil. Nendest uuringutest selgus, et dielektrikkilede sadestamine grafeenile, kasutades metallkloriid-vesi protsessi, põhjustab küll lateraalsete pingete tekkimist grafeenis, kuid ei genereeri struktuuridefekte selle võres. Siiski esineb grafeeni pinnal oksiidikile nukleatsiooni viivitus, mis teeb keeruliseks pidevate õhukeste oksiidikihtide kasvatamise. See on tingitud mitte ainult nukleatsioonitsentrite vähesusest, vaid ka nende tiheduse tugevalt ebaühtlasest jaotusest üle grafeeni pinna.In this thesis, pristine and functionalized few-layer graphene (FLG)- and multilayer graphene (MLG)-based structures were prepared and characterized using various spectroscopy and high-resolution microscopy and methods. For this purpose, the FLG and MLG have been synthesized by chemical vapor deposition (CVD) on nickel catalyst, and the properties of the prepared graphene sheets have been compared to the single-layer graphene (SLG) obtained by CVD or micromechanical exfoliation of natural graphite. The dependence of the graphene growth on the thickness and crystallographic orientation of the nickel substrate has been shown. It has been found that MLG synthesized on polycrystalline nickel is characterized by a variety of stacking order between the graphene layers presented in the sheets. It should be pointed out that if the rotation angles in synthesized MLG are larger than the critical angle of ~13 degrees, the Raman spectrum even of MLG becomes similar to the spectrum of SLG. The pronounced morphological changes of the nickel substrate accompanied the graphene growth has been demonstrated as well. Further, the electrochemical properties of the synthesized MLG sheets on nickel have been studied, and the possibility of their subsequent functionalization using electroreduction of various diazonium salts has been examined. It has been found that the CVD-grown graphene on nickel can be used as electrochemically passive supporting material for exploring new electro-catalytically active materials. The surface of the CVD-grown graphene can be further modified with aryl groups using electroreduction of diazonium salts, which allows broadening the use of the synthesized MLG. In addition, the feasibility of the chloride-water atomic layer deposition (ALD) of gate dielectric on top of nonfunctionalized graphene has been explored. It has been found that the deposition of dielectric films with the chloride-water ALD processes leads to a compressive strain of graphene but does not generate structural defects in the lattice. Still, there is a delay in the nucleation of the oxide layer on graphene, caused by the fact that the nucleation sites are not only at a deficit on graphene, but their density varies considerably. This makes it much more challenging to achieve the growth of a continuous oxide layer on graphene.https://www.ester.ee/record=b528236

The electrodeposition and characterisation of compositionally modulated tin-cobalt alloy coatings as lead-free plain bearing material

Traditionally, lead-based bearing overlays dominate the commercial automotive market and it has been proven that an excellent combination of properties can be attained through their use. However, lead is a toxic metal and a cumulative poison in humans. According to the European Union End-of-Life Vehicle (ELV) Directive proposed in 1997, vehicles that registered in'all the member states after 1st July 2003 should contain no lead, mercury, cadmium and hexavalent chromium. In this study, a new sulphate-gluconate electrolyte was used to produce multilayer SnCo coatings, aimed at a lead-free overlay for future market use. Tin-cobalt compositionally modulated alloy (CMA) coatings produced from sulphategluconate electrolytes have been previously examined as a potential replacement for lead-free bearing overlays [1]. However, some obstacles may exist which limit their potential use on an industrial scale. For example, long electroplating times are required to produce a thick coating which is very undesirable from an industrial viewpoint, and also the possible elemental interdiffusion occurring in the coating system under engine operating temperatures could rapidly deteriorate the coating properties. In addition, there is an increasing demand from automotive industry to further improve bearing overlay properties, for example for high performance and high compression ratio engines... cont'd

Protective and Functional Coatings for Metallic and Ceramic Substrates

This selection of ten papers, published in 2019 by researchers and institutions based in various countries around the world, allows an appreciation of the variety and significance of ongoing research in the wide field of protective and functional coatings. The most noteworthy investigations conducted in the area of surface protection are currently proceeding at a similar rapid pace in a twofold direction toward deeper and increasingly reliable knowledge of degradation and protection mechanisms as well as technological optimization of the selection and design of new materials, coating deposition processes, and characterization methods. This summarized collection serves as a representative essay of the collective worldwide efforts toward the development of more durable surfaces. Both organic and inorganic coatings are included among the protection strategies from a large variety of deposition processes, with interesting examples of organic–inorganic composites being proposed. Major attention is devoted to protection from both electrochemical and chemical corrosion of different metallic alloys and to advanced SiC-SiC composites exposed to the aggressive environments of gas turbines. Examples of modelling of wear corrosion examples are also reported. A dedicated space was intentionally devoted to the selection of papers detailing examples of the applicability of advanced characterization techniques. As an example of the wide field of research on innovative functional coatings, one study presents Mo alloys as an electrocatalytic material for the hydrogen evolution reaction. A comprehensive review of directed energy deposition additive manufacturing of metallic components completes this collection

Experimental Characterization and Synthesis of Nanotwinned Ni-Mo-W Alloys

Microelectromechanical systems (MEMS) have transformed consumer and industrial products through the integration of mechanical and electrical components within a single package. MEMS are ubiquitous in society, found predominantly in consumer electronics and automotive industries, providing interconnectivity across a wide variety of devices and everyday objects. To date, the materials selection for the structural element of many MEMS devices has been limited to a relatively small subset of materials, with silicon being the dominant choice. Employing MEMS sensors and switches in extreme environments will need advanced materials with a synergistic balance of properties, e.g. high strength, density, electrical conductivity, dimensional stability, and microscale manufacturability, but MEMS materials with this suite of properties are not readily available. Metallic systems are especially attractive for these applications due to their high density, strength and electrical conductivity. For this reason, metal MEMS materials are the motivation and focus for this dissertation. The synthesis of nanotwinned nickel-molybdenum-tungsten (Ni-Mo-W) alloys resulted in thin films with a very favorable suite of properties. Combinatorial techniques were employed to deposit a compositional spread of Ni85MoxW15-x, alloys and to investigate their physical and mechanical properties as a function of alloy chemistry. The addition of Mo and W was shown to significantly decrease the coefficient of thermal expansion (CTE) and provide a route for tailoring the CTE and its temperature dependence with compositional control. The measured CTE values for Ni-Mo-W matched that of commercial glass substrates currently employed in MEMS devices, broadening the spectrum of materials with the requisite dimensional stability for use in layered structures. Microscale mechanical testing was used to measure the in-plane tensile properties; a linear-elastic response with fracture strengths ranging from 2-3 GPa was uncovered. The ultrahigh tensile strengths are attributed to the presence of highly-aligned nanotwins and their effectiveness as obstacles to dislocation motion. In situ micropillar experiments demonstrated compressive strengths of 3-4 GPa and extremely localized plasticity, both of which are strongly orientation dependent. The nanoscale twins underpinning this mechanical behavior do not impede motion of electrons, and nanotwinned Ni-Mo-W thin films were found to posses the electrical conductivity of bulk Ni alloys. Taken as a whole, this study highlights the balance of physical, thermal and mechanical properties for Ni-Mo-W, driven by nanoscale twin formation. Deposition of Ni-Mo-W films displayed a wide processing window for the formation of the requisite nanotwinned microstructure and attendant properties (CTE, strength, ductility and electrical resistivity). Microcantilever beams were designed and fabricated using traditional integrated circuit processing to translate thin film properties into prototype MEMS device structures. Laser interferometry was used to certify the dimensional stability of the cantilever beams as-fabricated and after thermal exposure at elevated temperatures associated with wafer bonding. Micromachined cantilever beams showed excellent dimensional stability with beam deflection profiles on the order of tens of nanometers, elucidating a path beyond outstanding material properties to actual device structures for next generation metal MEMS devices

Effects of Plastic Deformation From Ultrasonic Additive Manufacturing

Nuclear energy technology can be exponentially advanced using advanced manufacturing, which can drastically transform how materials, structures, and designs can be built. Ultrasonic Additive Manufacturing (UAM) represents one of the four main additive manufacturing methods, although it is also the newest. As UAM technology and applications develop, a fundamental understanding of the bonding mechanism is crucial to fully realize its potential. Currently UAM bonding is considered to occur through breaking down surface asperities and removing surface oxides. Plastic deformation occurs although its role is currently unclear. This research analyzes material configurations in a variety of geometries, with similar and dissimilar material interfaces, and with pure metals and complex engineered materials. A variety of characterization techniques were used to develop a general description that UAM bonding requires plastic deformation. First, we analyzed various dissimilar material interfaces created between UAM foils and the coating of embedded optical fibers. Enhanced interdiffusion of elements was found beyond that expected from the thermal profile experienced during bonding. This interdiffusion was rationalized based on enhanced point defect vacancies creating additional diffusion pathways. Following on this study, we analyzed the local strengthening at one of these interfaces. These interfaces strengthened through a complex interaction dominated by dislocation forest hardening, reduced grain sizes, and vacancy clusters created by the agglomeration of vacancies. UAM bonding of pre-treated Al 6061 was also performed and analyzed using multi-length scale characterization. Macroscale strengthening was observed as well as foil-foil interface strengthening. This was a result of dynamic recrystallization, dynamic recovery, adiabatic heating, and precipitate dissolution (as the vacancies allowed enhanced diffusion of elements). Finally, UAM bonding of titanium was analyzed. The HCP phase of titanium significantly resisted plastic deformation, which resulted in a phase transformation to the BCC phase, which was stabilized by the introduction of certain stabilizing elements. The strain induced phase transformation and enhanced vacancy driven interdiffusion were utilized to demonstrate a viable method of improving UAM bonding by focusing on the plastic deformation requirement. The phenomena outlined in this research demonstrates an improvement in our understanding of the fundamental bonding requirements of UAM, and deformation induced vacancy formation