No description available.

Wood plastic composite (WPC) materials have seen a continuous market growth worldwide in the last decade. So-called extruded WPC profiles are today mainly used in outdoor applications, e.g. decking, railing and fencing. In outdoor conditions, moisture sorption in the wood component combined with temperature induced movements of the polymer matrix causes deformations of such composites. On the macroscopic scale this may lead to unacceptable warp, cup and bow of the WPC products, but on a microscopic scale, the movements will cause interfacial cracks between the particles and the matrix, resulting in little or no ability to transfer and re-distribute loads throughout the material. Moisture within the composite will also allow fungi and micro organisms to attack the wood particles. The conceptual idea of this work is to use a chemically modified wood component in WPCs to enhance their long term performance. These chemically modified wood particles exhibit reduced susceptibility to moisture, resulting in better dimensional stability and a higher resistance to biological degradation as compared to that of unmodified wood. The objective of this thesis is to study the effects of using modified wood in WPCs on their moisture sorption behaviour, micromorphology and microbiological durability. The modification methods used were acetylation, heat treatment and furfurylation. Equilibrium moisture content (EMC) and sorption behaviour of WPCs were determined by water vapour sorption experiments. The use of thin sections of the composites enabled EMC to be reached within a comparably short time span. The micromorphology was studied by LV-SEM (low vacuum-scanning electron microscope) using a specially designed sample preparation technique based on UV laser. The biological durability was evaluated by laboratory fungal test methods. The moisture sorption experiments showed lower moisture levels for all the composites when modified wood particles were used. This was also reflected in the micromorphological studies where pronounced wood-plastic interfacial cracks were formed due to moisture movement in the composites with unmodified wood particles. The sample preparation technique by UV laser proved to be a powerful tool for preparing surfaces for micromorphological studies without adding mechanical defects caused by the sample preparation technique itself. Results from the durability test showed that WPCs with modified wood particles are highly resistant to decay by fungi. / QC 20101116

<p> Environmental Barrier Coatings (EBCs) protect ceramic gas turbine engine components from corrosion by high temperature water vapor, but the coatings often form complex metastable microstructures upon plasma spray deposition. In ytterbium disilicate (YbDS) and its yttrium-doped counterpart (Y/YbDS), two coatings compatible with SiC/SiC parts, plasma spray forms a largely cracked, mechanically weak amorphous phase comprising up to ~80% of the coating’s volume. Therefore, the coatings must undergo a pre-service heat treatment to crystallize into stable phases and heal cracks. During the treatment, however, interplay between thermal expansion and crystallization contraction can cause vertical cracks which expose the component to the corrosive atmosphere. Remedial treatments with long, high temperature holds (~1300 ºC) can both crystallize the coating and heal existing cracks. However, these temperatures cause unnecessary grain growth that reduces the structural integrity of the coating over its lifetime.</p> <p>Here we propose an alternate heat treatment informed by experiments and modelling that removes metastable phases, heals cracks, and reduces time at temperature to prevent significant grain growth. First, we determine crystallization and phase change kinetics by applying the Ozawa-Flynn-Wall and Vyazovkin kinetic methods to differential scanning calorimetry (DSC) data. Next, we track locations and microstructural effects of phase evolution using correlative Raman spectroscopic mapping, scanning electron microscopy (SEM), and X-Ray diffraction (XRD). We interpret the formation of three distinct phases – a major phase of stable β-YbDS, and minor phases of stable Χ2-YbMS and metastable α-YbDS – within the existing framework of kinetic theory and quantify differences in their transformations between YbDS and Y/YbDS. We find that cracks in the coating heal through the crystallization of the amorphous phase and the transformation of the metastable phase although the mechanisms remain unclear. Each phase transformation causes a bulk volumetric change which we measure using dilatometry and use to calculate delamination stresses during a simulated heat treatment. Lastly, we determine the viability of our heat treatment compared to the industry standard.</p>

Blomsterlupin (Lupinus polyphyllus) är en iögonfallande invasiv växtart som i nuläget är spridd över större delen av Sverige utom nordvästra delen av Norrbotten. Framtagande av effektiva bekämpningsmetoder är av stor betydelse eftersom spridning av blomsterlupin hotar känsliga naturhabitat, exempelvis så kallade artrika vägkanter. Detta arbete fokuserar på värmebehandling, en metod som potentiellt kan användas för desinfektion av lösa jordmassor, som anses vara en av de största spridningsvektorerna för blomsterlupin. Arbetets syfte är att med hjälp av uppsamlade data undersöka om det finns en optimal temperatur och exponeringstid för effektiv minskning av antalet grodda blomsterlupinfrö. Utöver detta, utvärderas effekterna av förbehandling i form av rispning och blötläggning av frön. Inom experimentet behandlades blomsterlupinfrö med olika temperatur under olika exponeringstid. Hälften av fröna fick förbehandling i form av blötläggning efter rispning av skalet inför uppvärmningen. Frön värmebehandlades i 88˚C, 93˚C, 98˚C och 103˚C under 1, 3, 5 och 10 minuters tid. Efter värmebehandlingen fick fröna gro i ett odlingskåp. Resultatet visar att förbehandling, ökad temperatur och ökad exponeringstid bidrar till signifikant minskning av andel grodda blomsterlupinfrö. Ju högre temperaturen var, desto större var effekten av längre exponeringstid. Effekten av hög temperatur och lång exponeringstid var starkare om fröna var förbehandlade. Resultatet tyder på att värmebehandling potentiellt är en effektiv metod för bekämpning av blomsterlupinfrö. Vidare experiment krävs för att undersöka hur denna metod kan effektiviseras och tillämpas i praktiken, i synnerhet vid uppvärmning av stora volymer av jordmassor. / Garden lupine (Lupinus polyphyllus) is an eye-catching invasive herb that is currently spread over the major part of Sweden except for the northwestern part of Norrbotten county. The development of effective control methods is of great importance because the spread of Garden lupine threatens sensitive natural habitats, for example species rich road verges. This work focuses on heat treatment, a method that can potentially be used for the disinfection of soil masses, which is considered one of the major dispersal vectors for Garden lupine. The purpose of this work is to use the collected data to investigate whether there is an optimal temperature and duration of exposure for effective reduction of the number of germinated Garden lupine seeds. In addition, this work evaluates the effects of pre-treatment in the form of scarifying and soaking of seeds. Within the experiment, Garden lupine seeds were treated with different temperatures and different duration of exposure. Half of the seeds received pre-treatment in the form of soaking after scarifying the seed coat before heating. After that, seeds were heat treated at 88˚C, 93˚C, 98˚C and 103˚C for 1, 3, 5 and 10 minutes. After the heat treatment, the seeds were allowed to germinate in a growth chamber. The result shows that pre-treatment, increased temperature and increased exposure time contribute to a significant reduction in the percentage of germinated Garden lupine seeds. The higher the temperature, the stronger was the effect of a longer exposure time. The effect of high temperature and long exposure time was stronger if the seeds were pre-treated. The result suggests that the heat treatment is potentially an effective control method for Garden lupine seed. Further experiments are required to investigate if this method could be made more efficient and applied in practice, particularly when heating large volumes of soil masses.

The demand for Advanced High Strength Steel (AHSS) in the automotive industry is increasing day by day. It is mainly motivated by the fact that AHSS can be used as thin sheets while having high strengths. It enables weight reduction of the automobiles which consequently increases the fuel efficiency and has proven to be less harmful to the environment. It is also expected that AHSS will have even higher strength in the near future. Cold work tools steels with 5 wt.% Cr are commonly used to process AHSS. Therefore, the tool steel must meet the challenges in the future, i.e. have even higher hardness, compressive strength and toughness. One way of increasing the mechanical properties of the tool steel is by improving the heat treatment parameters. However, it is not possible without a deeper understanding of the heat treatment process. Therefore, this work presents investigations related to phase transformations occurring in a 5 wt.% Cr cold work tool steel during heat treatment. Furthermore, the influence of austenitisation and tempering temperatures on the microstructure and mechanical properties were investigated. The studies revealed that a higher austenitisation temperature can be used to achieve a higher hardness, good compressive strength and adequate toughnessof the steel. However, too high austenitisation temperature may result inexcessive coarsening of prior austenite grains which reduced the impact toughness. It was also found that retained austenite can transform during tempering by two different mechanisms. Firstly, when tempering at 525°C, carbides precipitate in retained austenite lowering its stability and permitting a transformation to marten site on cooling. Secondly, when tempering at 600°Cfor extended holding time retained austenite isothermally transforms to ferrite and carbides. This occurs by precipitation of carbides in retained austenite followed by a final transformation to ferrite and carbides.These results were used to understand the standard tempering procedure of the 5 wt.% Cr cold work tool steel. Furthermore, alternative heat treatment procedures are discussed based on the important findings presented in this thesis.

Uppvärmning av stål kan leda till korntillväxt vilket har en avgörande roll på materialets mekaniska egenskaper och generellt sett så resulterar det i sämre hållfasthet. I följande examensarbete har olika modeller tagits fram för att prediktera förändringar i kornstorleken som sker till följd av sätthärdning. Modellerna tas fram via en litteraturöversikt och är ämnade att prediktera korntillväxt på provbitar med tillsatser av Niob samt provbitar utan Niob. Målet med detta examensarbete är att undersöka vilka modeller som finns tillgängliga för att prediktera korntillväxt samt analysera hur predikteringen ser ut i jämförelse med observationsvärden från experimentella försök. Examensarbetet består av en experimentell del och en modelleringsdel. Den experimentella delen sker genom att provbitar analyseras med hjälp av ljusoptisk mikroskopi med avseende på förändringar i kornstorlek före och efter värmebehandling. Detta för att kunna estimera förändringar i kornstorlek och validera beräkningsmodellerna för prediktering av förändringar i kornstorlek. Modelleringsdelen används för att testa hur olika modeller predikterar korntillväxten. Beräkningsdelen och den experimentella delen jämförs sedan med varandra i resultatet där en sammanställning på alla värden sker. Resultatet visar vilka modeller som finns tillgängliga för att prediktera korntillväxt samt hur predikteringarna ställer sig mot observationsvärden från experimentella prover.  För att säkerställa att modellerna kan användas för att prediktera korntillväxten så krävs en djupare analys av modellerna då alla materialparametrar inte kunde tas fram till samtliga modeller. En utveckling av arbetet är att ta fram alla parametrar för att sedan kunna avgöra vilken modell som ställer sig närmast till uppmätta värden från den experimentella delen. / Heating steel may lead to grain growth, which results in deterioration of mechanical properties of the steel. In the present study, different models that predict changes in grain size, occurring in heat treatments such as case hardening, have been validated. The models were retrieved via a literature review and were intended to predict grain growth on test pieces with and without Niob precipitates. The aim of this thesis is to investigate which models that are available for predicting grain growth and to validate the models in a comparison with experimental results. This thesis consists of an experimental part and a modeling part. The experimental part is done by analyzing specimens using light-optical microscopy regarding changes in grain size before and after heat treatment. This is to be able to estimate changes in grain size and validate calculation models for predicting changes in grain size. The modeling part is used to evaluate how different models predict grain growth. The calculation part and the experimental part then compare with each other in the result where a compilation of all values takes place. The results show which models are available for predicting grain growth and how the predictions compare with observation values from experimental samples. To ensure that the models can be used to predict grain growth, a deeper analysis of the models is required; not all material parameters could be obtained for all models. A development of the work is to retrieve all parameters in order to then be able to determine which model is closest to the measured values from the experimental part.

In new low-lead and lead-free brass alloys, it is not understood how the corrosion properties,such as dezincification, are related to material composition as well as annealing temperatureand duration. This study aims to fill this knowledge gap by mapping sixteen annealingconditions and three different brass alloy compositions to their respective microstructure anddezincification performance. It was found that high dezincification depth was a result ofannealing temperatures at 300°C – 400°C, which promoted precipitation of intermetallicAlAs-particles along grain boundaries, twins and lead particles as well as precipitation of β-phase along grain boundaries. Their presence was correlated to high micro additions ofaluminium or iron in the material composition. An additional compositional factorcontributing to precipitation of high amount of β-phase was low copper/zinc-ratio.

Haynes 282 is a gamma prime (𝛾′)-strengthened nickel base superalloy developed in 2005, exhibiting a good combination of high temperature properties and fabricability. Microstructural features such as 𝛾′ and carbides play an important role in deriving the mechanical properties of the alloy during heat treatment. As Haynes 282 is a relatively new alloy with insufficient literature availability, the present thesis is aimed at studying the evolution of microstructure for different heat treatment times and temperature with a special focus on 𝛾′ phase precipitation kinetics with different initial conditions for the material. The study is divided into two sections with objectives which are focused on the different ends to the heat-treatment time scales. The first objective of this study was to investigate γ' precipitation at short heat treatment times and develop Time-Temperature Precipitation (TTP) and Hardness (TTH) diagrams for Haynes 282 using a novel arc heat treatment. In this technique, a steady state temperature gradient, covering room temperature to liquidus, was created using stationary TIG arc on a disc mounted on a water-cooled chamber. Aged and solutionized samples were arc heat treated for 1.5 minutes, 30 minutes and 4 hours. The study was complemented with temperature modelling, thermodynamic calculations, and 𝛾′ precipitation simulation. A unique graded microstructure formed, consisting of dendritic region in fusion zone; dissolution area of all phases including MC carbides, grain boundary carbides, and 𝛾′; grain boundary carbide zone, 𝛾′ band; and base metal. 𝛾′ precipitate size increased with increasing time and temperature. 𝛾′ precipitation simulation model was developed, and it showed very good agreement with experimental results. Finally, the results were summarized in TTH and TTP diagrams. The second objective in this work was to study understand the coarsening behaviour of 𝛾′ phase with an initial pre-heat-treated GKN heat treatment using furnace heat treatment. Isothermal heat treatments for temperatures from 800°C to 1120°C and times from 30 seconds to 96 hours were performed. Morphological changes in 𝛾′ phase, particle size distribution, grain sizes and hardness on these isothermal heat-treated states are presented in this work. Additionally, A TC PRISMA precipitation model was evaluated to predict 𝛾′sizes and compare it with the measurements. It was concluded that complex initial microstructure, containing bimodal distribution of 𝛾′ precipitates, caused deviations between predicted and measured values, while the model, in the previous objective, predicted the sizes in close approximation to the experimental values. Therefore, further understanding and development of precipitation kinetics with the software should be done to achieve closer results to the experiment. / Haynes 282 är ett gamma prime (𝛾′) - förstärkt superlegering av nickelbas som utvecklades 2005 och uppvisar en god kombination av högtemperaturegenskaper och tygbarhet. Mikrostrukturella egenskaper såsom 𝛾′ och karbider spelar en viktig roll för att få de mekaniska egenskaperna hos legeringen under värmebehandling. Eftersom Haynes 282 är en relativt ny legering med otillräcklig litteraturtillgänglighet syftar den aktuella avhandlingen till att studera utvecklingen av mikrostruktur för olika värmebehandlingstider och temperatur med ett särskilt fokus på 𝛾′ fasutfällningskinetik med olika initiala förhållanden för materialet. Studien är uppdelad i två sektioner med mål som är inriktade på de olika ändarna på värmebehandlings tidsskalorna. Det första syftet med denna studie var att undersöka 𝛾′nederbörd vid korta värmebehandlingstider och utveckla Time-Temperature Precipitation (TTP) och Hardness (TTH) diagram för Haynes 282 med användning av en ny bågvärmebehandling. I denna teknik skapades en jämn temperaturgradient, som täcker rumstemperatur till liquidus, med användning av stationär TIG-båge på en skiva monterad på en vattenkyld kammare. Åldriga och lösningsbara prover bågvärmebehandlades under 1,5 minuter, 30 minuter och 4 timmar. Studien kompletterades med temperaturmodellering, termodynamiska beräkningar och 𝛾′utfällningssimulering. En unik graderad mikrostruktur bildad, bestående av dendritisk region i fusionszon; upplösningsområde för alla faser inklusive MC-karbider, korngränsande karbider och 𝛾′; korngränsen karbidzon, 𝛾′ band; och oädel metall. 𝛾′utfällningsstorlek ökade med ökande tid och temperatur. 𝛾′utfällningssimuleringsmodell utvecklades, och den visade mycket bra överensstämmelse med experimentella resultat. Slutligen sammanfattades resultaten i TTH- och TTP-diagram. Det andra syftet med detta arbete var att studera förstå det förgrovning beteendemönster hos 𝛾′ fasen med en initial förvärmebehandlad GKN-värmebehandling med ugnsvärmebehandling. Isotermiska värmebehandlingar för temperaturer från 800 ° C till 1120 ° C och gånger från 30 sekunder till 96 timmar utfördes. Morfologiska förändringar i 𝛾′fasen, partikelstorleksfördelning, kornstorlekar och hårdhet på dessa isotermiska värmebehandlade tillstånd presenteras i detta arbete. Dessutom utvärderades en TC PRISMA-nederbördsmodell för att förutsäga 𝛾′ storlekar och jämföra den med mätningarna. Det drogs slutsatsen att komplex initial mikrostruktur, innehållande bimodal fördelning av 𝛾′-fällningar, orsakade avvikelser mellan förutspådda och uppmätta värden, medan modellen i det tidigare målet förutspådde storleken i nära anpassning till experimentvärdena. Därför bör ytterligare förståelse och utveckling av utfällningskinetik med programvaran göras för att uppnå närmare resultat till experimentet.

No description available.

The work presented has the ultimate aim to increase dynamic mechanical properties by improvements in density and optimisation of microstructure of ultra high carbon PM steels by careful selection of processes, i.e. mixing, binding, alloying, heating profile and intelligent heat treatment. ThermoCalc modelling was employed to predict liquid phase amounts for two different powder grades, Astaloy 85Mo or Astaloy CrL with additive elements such as (0.4-0.6wt%)Si, (1.2-1.4wt%)C and (1-1.5wt%)Mn, in the sintering temperature range 1285-1300ºC and such powder mixes were pressed and liquid phase sintered. In high-C steels carbide networks form at the prior particle boundaries, leading to brittleness, unless the steel is heat-treated. To assist the breaking up of these continuous carbide networks, 0.4-0.6% silicon, in the form of silicon carbide, was added. The water gas shift reaction (C + H2O = CO + H2, start from ~500ºC) and Boudouard reaction (from ~500ºC complete ~930ºC) form CO gas in the early part of sintering and can lead to large porosity, which lowers mechanical properties. With the use of careful powder drying, low dew point atmospheres and optimisation of heating profiles, densities in excess of 7.70g/cm3 were attained. The brittle microstructure, containing carbide networks and free of cracks, is transformed by intelligent heat treatment to a tougher one of ferrite plus sub-micron spheroidised carbides. This gives the potential for production of components, which are both tough and suitable for sizing to improve dimensional tolerance. Yield strengths up to 410 MPa, fracture strengths up to 950 MPa and strains of up to 16 % were attained. Forging experiments were subsequently carried out for spheroidised specimens of Fe-0.85Mo+06Si+1.4C, for different strain rates of 10-3, 10-2, 10-1 and 1sec-1 and heated in argon to 700¿C, density ~7.8g/cm3 and 769 MPa yield strength were obtained. / Libyan Education Ministry Office