<p>Lead chalcogenides and tin chalcogenides and their alloys are IV−VI family semiconductors with unique material properties compared with similar semiconductors. For instance, Pb<i>Y </i>(<i>Y </i>= S, Se, and Te) are narrow-gap semiconductors with anomalous negative pressure coefficient and positive temperature coefficient. It is known that this behavior is related with the symmetry of wave functions in first Brillouin zone L-point, which moves the edges of valence band maximum and conduction band minimum towards each other with pressure increasing. SnTe has opposite behavior since its wavefunction symmetry is different from Pb<i>Y</i>. Therefore, by alloying PbTe and SnTe one can change and control the band gap energy and its pressure or temperature dependence. These chalcogenides alloys have therefore a huge potential in industrial low-wavelength applications and have been attracted the attention of researchers.</p><p>This thesis comprises theoretical studies of Pb<i>Y</i>, Sn<i>Y</i> (<i>Y </i>= S, Se and Te) and the Pb₁−<i>x</i>Sn<i>x</i>Te alloys (<i>x</i>= 0.00, 0.25, 0.50, 0.75, and 1.00) by means of a first-principles calculation, using the full-potential linearized augmented plane waves method and the local density approximation.</p><p>The optical properties of Pb₁−<i>x</i>Sn<i>x</i>Te alloys are investigated in terms of the dielectric function <i>ε</i>(<i>ω</i>) = ε₁(<i>ω</i>) + <i>iε</i><i>2</i><i>(ω</i>). We find strong optical response in the 0.5–2.0 eV region arising from optical absorption around the LW-line of the Brillouin zone. The calculated linear optical response functions agree well with measured spectra from ellipsometry spectroscopy performed by the Laboratory of Applied Optics, Linköping University. The calculations of the electronic band-edges of the binary PbY and SnY compounds, show similar electronic structure and density-of-states, but there are differences of the symmetry of the band-edge states at and near the Brillouin zone L-point. PbY have a band gap of E<i>g</i><i> </i>0.15−0.30 eV. However, SnY are zero-gap semiconductors<i> E</i><i>g</i> = 0 if the spin-orbit interaction is excluded. The reason for this is that the lowest conduction band and the uppermost valence band cross along the LW line. When including in Pb<i>Y</i>. Although Pb<i>Y</i> and Sn<i>Y </i>have different band-edge physics at their respective equilibrium lattice constants, the change of the band-edges with respect to cell volume is qualitatively the same for all six chalcogenides. The calculations show that the symmetry of band edge at the L-point changes when lattice constant varies and this change affects the pressure coefficient. the spin-orbit interaction a gap <i>E</i><i>g</i><i> </i>≈ 0.2 eV is created, and hence this gap is induced by the spin-orbit interaction. At the L-point, the conduction-band state is a symmetric state and the valence-band state is antisymmetric thereby the L-point pressure coefficient ⁺₄L−₄Lp<i>E</i><i>g</i>∂∂/)L( in SnY is a positive quantity. In contrast to Sn<i>Y</i>, the Pb<i>Y</i> compounds have a band gap both when spin-orbit coupling is excluded and included; this gap is at the L-point, and the conduction-band state has and the valence-band state has symmetry, and thereby this band edge yields the characteristic negative pressure coefficient ⁺₄L−₄Lp<i>E</i><i>g</i>∂∂/)L(</p>

No description available.

<p>The understanding of the hardenability is important in steel development with respect to weldability of steels as well as to the design of quenched and tempered steels.The common way to judge if steel is suitability to welding is the use of a carbon equivalent, which reflects the alloy content to the hardenability of the heat affected zone (HAZ). Most common of these equivalent is the IIW carbon equivalent wich has been in use for decades.</p><p>However, this is an empirical equivalent, developed for CMn steels, and it doesn't say anything about the mechanical properties obtained in the HAZ. As a guideline a maximum HAZ hardness of 350 HV is normally put to avoid cold cracking in the HAZ. Numerous carbon equivalents have been published during the years, but few have been accepted and used. A drawnback of all these equivalents is that they have been evaluated for a set of chemical compositions which may be quite narrow, or that they have been evaluated on steels produced having other cleanliness, residual element levels etc. as is common in modern steelmarketing. </p><p>The hardenability of steel designated to quenching and tempering is normally evaluated using either Jominy testing or using a calculation using the Grossmann formalism. As the hardenability described in the carbon equivalents used in welding and the hardenability of quenched and tempered steels using the Grossmann formalism are two different descriptions of the same phenomenon the aim of this thesis is to link these two formalisms together and use the knowledge from the HAZ hardenability to design quenched and tempered steels. The goal is to produce such steel grades having a much better weldability as compared with standard grades available at the market. </p><p>In this work the hardenability in the heat affected zone (HAZ) in weldments in high strength low alloyed steels (HSLA steels) having a yield strength of 350 MPa. This part microalloying elements on the phase transformations which take place during cooling from the peak temperature of the welding cycle. These results have been linked to the mechanical properties of the HAZs. </p><p>In the second part of this thesis the development of tool steel grades with respect to optimise both hardenability with respect to; </p><p>- matrix hardenability (i.e the Grossmann approach) </p><p>- an enhanced weldability of such new steels due to a lower alloying content than is usual in such grades</p>

<p>Case hardening distortions are a major problem for gear manufacturers. The aim of the current work is to create a simulation model, able to predict how and when case hardening distortions arise. The results presented in this thesis form a basis for such a model.</p><p>Two case hardening steels, with base carbon contents of 0.20 and 0.21 % C were studied using dilatometer experiments. One of them was carburized to 0.36, 0.52 and 0.65 % C in order to investigate the influence of carbon content. Experiments were performed during both isothermal and continuous heating and cooling conditions. The results were used to evaluate phase transformations, heat expansion behaviors and phase transformation strains. The expansion behavior of the material was modeled as a function of temperature, carbon content and phase fractions. The phase transformations to martensite and bainite were modeled, using the Koistinen-Marburger equation and a transformation rate equation based on Austin-Rickett kinetics, respectively. Experiments were simulated using the COMSOL Multiphysics software, to verify the model with respect to martensite and bainite transformations, heat expansion behavior and phase transformation strains.</p>

This Thesis presents two different deposition techniques for the synthesis of Ti2AlC coatings. First, I have fabricated Ti2AlC coatings by high velocity oxy-fuel (HVOF) spraying. Analysis with scanning electron microscopy (SEM) show dense coatings with thicknesses of ~150 µm when spraying with a MAXTHAL 211TM Ti2AlC powder of size ~38 µm in an H2/O2 gas flow. The films showed good adhesion to stainless steel substrates as determined by bending tests and the hardness was 3-5 GPa. X-ray diffraction (XRD) detected minority phases of Ti3AlC2, TiC, and AlxTiy alloys. The use of a larger powder size of 56 µm resulted in an increased amount of cracks and delaminations in the coatings. This was explained by less melted material, which is needed as a binding material. Second, magnetron sputtering of thin films was performed with a MAXTHAL 211TM Ti2AlC compound target. Depositions were made at substrate temperatures between ambient and 1000 °C. Elastic recoil detection analysis (ERDA) shows that the films exhibit a C composition between 42 and 52 at% which differs from the nominal composition of 25 at% for the Ti2AlC-target. The Al content, in turn, depends on the substrate temperature as Al is likely to start to evaporate around 700 °C. Co-sputtering with Ti target at a temperature of 700 °C, however, yielded Ti2AlC films with only minority contents of TiC. Thus, the addition of Ti is suggested to have two beneficial roles of balancing out excess of C and to retain Al by providing for more stoichiometric Ti2AlC synthesis conditions. Transmission electron microscopy and X-ray pole figures show that the Ti2AlC grains grow in two preferred orientations; epitaxial Ti2AlC (0001) // Al2O3 (0001) and with 37° tilted basal planes of Ti2AlC (101̅7) // Al2O3 (0001). / Report code: LIU-TEK-LIC-2008:15.

AB SOMAS Ventiler manufactures valves for different applications. A valve of type DN VSSL 400, PN 100, used in high-temperature and high-pressure applications was investigated in this thesis. This type of valve is coated with high cobalt alloys to achieve the tribological properties needed for this severe condition. However there is a request from AB Somas Ventiler to find another solution. This request is based on the fact that demands on higher temperatures, from customers, yields higher requirements on the material. It is also a price issue since cobalt is quite expensive. Materials investigated were high-nitrogen steel, Vanax 75, nickel-based superalloy Inconel 718 and hardened steels, EN 1.4903 and EN 1.4923 presently used as base material in the valve. Calculation of contact pressure that arises when the valve is closed was first approached by using finite element method (FEM). Several models were constructed to show the behavior of the valve during closing in terms of deformation. Hot wear tests, in which a specimen was pressed against a rotating cylinder, were performed to be able to compare the materials to the solution of today and among each other. Data extracted from the tests were compiled in the form of coefficients of friction. Profilometer examinations were used to reveal the volumes of worn and adhered material and together with scanning electron microscopy (SEM) the wear situation for each material couple could be assessed. Wear mechanisms detected in SEM were adhesive and abrasive and the results clearly showed that the steels were not a good solution because of severe adhesive wear due to the similarity of mating materials creating a more efficient bonding between the asperities. Vanax 75 showed much better performance but there was still an obvious difference between the steels and the superalloy in terms of both coefficient of friction and amount of wear. On this basis, Inconel 718 was selected as the most suitable material to replace the high cobalt alloys used in the valves today. / AB Somas ventiler är ett företag som tillverkar ventiler för ett brett spann av applikationer. I det här examensarbetet har undersökningar genomförts på en ventil av modell DN VSSL 400, PN 100, som normalt används i applikationer för höga tryck och höga temperaturer. Ventilen beläggs i dagsläget med höghaltiga koboltlegeringar för att uppnå de tribologiska egenskaper som krävs i de påfrestande arbetsförhållanden som råder. AB Somas Ventiler har dock framfört en förfrågan om att hitta en alternativ lösning, en förfrågan som grundar sig i att kundernas ständiga önskemål på att ventilerna ska klara högre arbetstemperaturer också medför högre krav på ventilmaterialen. Det är även en prisfråga, då kobolt är en dyr legering att använda sig av. De material som inkluderades i undersökningen var det kvävelegerade stålet Vanax 75, nickelbaserade superlegeringen Inconel 718 samt de två stålen EN 1.4903 och EN 1.4923 i härdat tillstånd. De två sistnämnda används idag som basmaterial i ventilen. Genom att använda den finita element metoden (FEM) kunde en första beräkning göras av det kontakttryck som uppstår då ventilen stängs. Flera modeller konstruerades för att simulera ventilens deformation vid stängning. Där efter utfördes nötningstester i hög temperatur på de alternativa materialen, genom att låta en provbit pressas mot en roterande cylinder, för att sedan kunna göra en jämförelse mellan materialen och även med den nuvarande lösningen. Från nötningstesterna erhölls data som kunde användas för att ta fram friktionskoefficienter för de olika materialparen. Med hjälp av undersökningar med profilometer och svepelektronmikroskop (SEM) kunde värden på nötta och vidhäfta volymer erhållas tillsammans med information om nötningssituationer för ytorna mellan de olika materialparen. De nötningsmekanismer som påvisades med hjälp av SEM-undersökningen var adhesiv och abrasiv nötning, och resultaten visade tydligt att nötningen av stålen var omfattande, på grund av att lika material i kontakt med varandra skapar starkare band mellan ytorna, och att de därför inte var en intressant lösning. Det kvävelegerade Vanax 75 uppförde sig visserligen bättre men en tydlig skillnad mot superlegeringarna kunde dock fortfarande konstateras, sett till både friktionskoefficient och mängden slitage. Baserat på dessa resultat valdes Inconel 718 som det bäst lämpade materialet att ersätta de höghaltiga koboltlegeringarna som idag används i ventilen.

<p>Tantalum diffusion barrier coatings were investigated as a way to improve the conversion efficiency of CIGS (copper indium gallium diselenide) solar cells.  Tantalum coatings were deposited upon silicon and stainless steel foil substrates using direct current magnetron sputtering (DcMS) and high power impulse magnetron sputtering (HiPIMS).  The coatings were characterized using scanning electron microscopy (SEM).  Cross-sectional scanning electron micrographs revealed that the HiPIMS coatings appeared denser than the DcMS coatings.</p>

<p>Summary</p><p>I have a great interest in bouzoukis and since I, during my education in guitar making, mainly have focused on building bouzoukis and other traditional folk instruments, I have chosen the bouzouki as the object of my degree project.</p><p>In connection to the making of these instruments, I started to consider the construction of the bouzouki and why the bouzouki has such a characteristic sound.</p><p>One of my theories is based on the fact that most bouzoukis are made with floating bridges instead of glued pinbridges. Do these types of bridges differ from each other tonally and if so, how much and in what way?</p><p>To receive answers to my questions, I have built two identical bouzoukis with different types of bridges, one with a glued pinbridge and one with a floating bridge. I have been very precise in the making of these instruments, giving them the exact same dimensions and using material from the same piece of wood. This to make sure that the instruments should be as exactly alike as possible.</p><p>After finishing the making of the bouzoukis, I arranged for a sound test where I let musicians play and listen to the instruments. After doing this I let the same musicians fill in a form with questions regarding each instruments tonal characteristics and it’s fields of application.</p><p>By compiling the answers from the sound test, I have come to a conclusion regarding what tonally separates a bouzouki with a glued pinbridge from a bouzouki with a floating bridge.</p><p>In addition to this I have found out what other instrument makers considers to be the difference between these two types of bridges.</p><p>Beside the project described above I also present a brief history of the bouzouki.</p> / <p>Sammanfattning</p><p>Jag har valt att göra ett examensarbete som grundar sig på mitt stora intresse för bouzoukis. Jag har under min utbildning i gitarrbyggeri främst riktat in mig på att bygga bouzoukis samt liknande folkinstrument. I samband med dessa byggen så har jag fundera mycket över instrumentets konstruktion och vad det är som gör att bouzoukin har ett så karakteristiskt ljud.</p><p>En av mina funderingar består i varför de flesta bouzoukis är utrustade med ett tryckande stall istället för ett limmat stall. Skiljer sig dessa stalltyper från varandra tonalt och i sådant fall hur mycket och på vilket sätt?</p><p>För att få svar på mina frågor har jag byggt två stycken bouzoukis som är identiskt lika bortsett från stalltypen. Den ena har ett limmat stall och den andra ett tryckande stall.</p><p>Jag har varit mycket noggrann med att tillverka bouzoukierna med exakt samma dimensioner och med material som kommer från samma trästock. Detta för att försäkra mig om att instrumenten ska bli så lika som det bara går.</p><p>Därefter har jag anordnat ett ”lyssningstest” där jag har låtit musiker spela och lyssna på instrumenten. Musikerna har sedan fått fylla i ett formulär innehållande frågor om instrumentens tonala egenskaper samt om deras användningsområden.</p><p>Genom att sammanställa svaren från lyssningstestet har jag kommit fram till en slutsats om vad det är som tonalt skiljer ett limmat från ett tryckande stall hos en bouzouki.</p><p>Jag har även att tagit reda på vad andra instrumentbyggare anser att det är för skillnader mellan de olika stalltyperna, samt hur bouzoukins historia i stora drag ser ut.</p>

<p>The processing of aluminium alloys from casting to end product is associated with a large number of metallurgical phenomena. In order to further improve and optimise process routes and alloys, a thorough understanding of the thermomechanical treatments by experimental observations and physically based modelling is necessary.</p><p>In part A of this thesis the work hardening behaviour of non-heat treatable alloys is followed up to large strains. The evolution in strength, microstructure and texture during cold rolling is analysed in commercially pure aluminium, AlMg alloys and AlMn alloys, covering both solid solution strengthening, particle strengthening, grain size effects and effects of impurities. A recently developed model for work hardening is applied to these alloys and discussed in relation to the experimental observations. The model successfully predicts the effects of Mg in solid solution, and is used to explain the effects of nonshearable particles and grain size on the strength and work hardening in stage II-III. Mn, Fe and Si in solid solution are suggested to create solute clusters that increase the strength significantly. At higher strains, stage IV, an unexpectedly low work hardening rate of high-Mg alloys is ascribed to a different storage pattern of dislocation and an increased amount of shear bands. High-resolution EBSD in FE-SEM is demonstrated to be a promising tool for substructure characterisation of cold rolled alloys.</p><p>In part B the mechanical anisotropy of flat extruded profiles of heat-treatable alloys is investigated. Two recrystallised alloys, AA6063 and 7030, and two non-recrystallised alloys, AA6082 and 7108, are tested in uniaxial tension in the solution heat treated condition, exhibiting strong directionality of yield stress, work hardening rate, elongation and r-value. The initial textures are very strong, and the anisotropy is analysed in terms of the Taylor model. The texture is found to be responsible for most of the strength anisotropy in the non-recrystallised alloys, while other sources of anisotropy must be present in the recrystallised alloys. Variations in the deformation structure development, indicating different slip activity in different directions, are believed to be partly responsible. The Taylor RC model predicts the r-values very well in all alloys, and a number of active slip systems in each position between two and three is assumed to be realistic for all alloys and directions.</p>

<p>This doctoral thesis is concerned with pitting corrosion in super martensitic stainless steel (SMSS) weldments in slightly sour service. Thee main objective with the present thesis has been to find out why pitting corrosion occurs in the heat affected zone (HAZ) at ambient rather than at elevated temperatures and how the corrosion mechanism depends on the welding process.</p><p>The thesis is divided into six parts. Part I gives a general introduction to martensitic stainless steels, focusing on the metallurgical and corrosion properties.</p><p>Part II is concerned with the conditions for initiating of pitting corrosion in two SMSS weldments. Optical microscopy in combination with sputtered neutral mass spectrometry has been used to examine the conditions, and it is shown that the corrosion resistance depends mainly on the nature of the surface oxide and less on the underlying microstructure. In the absence of H₂S the initiation is associated with spalling of the iron-enriched chromium oxide within a narrow region approximately 6mm from the fusion boundary, where the contaminated oxide layer is thinnest. As H₂S is introduced, the region close to the fusion boundary become susceptible to localised corrosion because of the more extensive metal oxidation. Thus, the high temperature oxidation and iron oxide scale formation accompanying the welding operation appears to be the main factor affecting the pitting corrosion initiation in SMSS weldments.</p><p>In Part III, a comparative study of the dissolution and repassivation behaviour of a Fe-12.3Cr-6.5Ni-2.6Mo SMSS alloy and other stainless grades has been carried out. The SMSS alloy is characterised by means of the so-called “artificial pit technique”, and a diffusion model has been developed and employed for calculation of the pit surface concentration of dissolved species during the potential step experiments. For concentrations close to the saturation level, the dissolution kinetics are adequately described by a Tafel slope of approximately 57mV/dec and a current density of 0.5mA/cm2 at –300mV SCE. On the other hand, repassivation of the active pit surface occurs when the concentration of the dissolved species drops below 30% of the saturation value. Based on a comparison with relevant literature data it is concluded that the observed response of the SMSS to localised corrosion is similar to that reported for other high-alloyed steels. This result is to be expected if the dissolution and repassivation kinetics are controlled by the content of Cr, Ni and Mo in the parent material.</p><p>In Part IV, the specific effects of H₂S on the pitting corrosion behaviour of a Fe-12.3Cr-6.5Ni-2.6Mo SMSS alloy have been examined by means of the “artificial pit technique”. Addition of a critical amount of H₂S is found to hinder repassivation and accelerate active dissolution in the SMSS pit within the stability domain of the adsorbed sulphur. Above the redox potential of H₂S/S, the effect of H₂S is found to cease, whereby dissolution and repassivation kinetics similar to H₂S-free solutions are observed. Activated pits show no signs of repassivation, not even at low surface concentration of dissolved species. It is concluded that the resistance to pitting corrosion depends both on the potential and the H2S concentration and the effect of H₂S is most significant at low potentials.</p><p>Part V is concerned with the occurrence and appearance of pitting corrosion in SMSS girth welds in the presence of H₂S. Galvanostatic and potentiodynamic measurements were carried out at ambient temperature and pressure, using both a deaerated solution and a 1mM H2S solution. In conjunction with this study, a descriptive pitting corrosion model is proposed to explain the effect of the root surface condition and the role of H₂S. The oxidized pipe surface close to the fusion boundary is found to be extremely vulnerable to pitting corrosion in the presence of H₂S, while the same zone appears to behave inert in the deaerated solution. In the latter case the oxidised surfaces were found to repassivate. In the H₂S solution, localized corrosion occurred in the most oxidized region of the HAZ, about 0 to 3mm from the fusion boundary. Moreover, it was found that a modification of the as-welded root surface by grinding hindered any initiation of pitting corrosion in this region, again highlighting the important role which high temperature oxidation and oxide scale formation play in controlling the corrosion properties of SMSS weldments. </p><p>Finally, in Part VI of the thesis, the practical implications of the above findings for choice and development of relevant corrosion test procedures have been considered. A key issue here is the effect of pre-exposure on the corrosion resistance of SMSS weldments in the presence of H₂S. Pre-exposures have been simulated in test solutions resembling the conditions in a flowline. It is shown that the quality (i.e. passivity) of SMSS root surfaces can be largely improved by the use of an appropriate pre-exposure procedure. It is therefore recommended that all samples in the future are pre-exposed to an H₂S-free solution before they are subjected to actual corrosion testing in solutions containing H₂S to avoid pitting corrosion in the oxidized part of HAZ. This is deemed to be important in order to achieve realistic results.</p>