Fatigue response of metallic materials is considered of significant importance, particularly for high-demanding applications. It is proved that most of the engineering materials do not exhibit a conventional fatigue limit in the high cycle fatigue regime, but rather display a continuously decreasing stress-life response at even longer lifetimes. Consequently, investigations of the various failure mechanisms taking place are essential, especially at the high and very high cycle fatigue regimes.The development of new ultrasonic testing equipment made the fatigue testing beyond 107 life cycles possible in a much shorter time, enabling testing with fatigue fractures at stress levels lower than the traditionally proposed “fatigue limit”. Nowadays, a classification of fatigue life regimes in Low Cycle Fatigue (LCF), High Cycle Fatigue (HCF) and Very High Cycle Fatigue (VHCF) is commonly used. The main reasons for this specific grading are: i) the need for safe design of components and ii) the fact that the failure mechanisms are particular in each of the LCF, HCF and VHCF regimes.The main goal of the present thesis is to address the fatigue response of high strength tool steels. Considering the novel alterations in composition and production methods in alloy development, materials of high-quality are continuously being introduced to the market; understanding the fatigue response of these materials is crucial for potential utilization across diverse industries and applications. The generation of fatigue experimental data, the analysis of the different types of fatigue initiation defects found in each material, as well as the investigation of the fatigue mechanisms occurring during cyclic loading are the main subjects analyzed throughout the present study. / Utmattningsegenskaper hos metalliska material anses vara av stor betydelse, särskilt för krävande tillämpningar. Det är visat att de flesta konstruktionsmaterial inte uppvisar en konventionell utmattningsgräns i området för högcykelutmattning, utan snarare uppvisar ett kontinuerligt minskande spänning-livslängd förhållande med längre livslängder. Följaktligen är undersökningar av de olika brottmekanismer som äger rum väsentliga, särskilt vid utmattningsregimer med höga och mycket höga livslängder.Utveckling av nya ultraljudsutrustningar gjorde utmattningsprovning utöver 107 livscykler möjliga på mycket kortare tid, vilket möjliggjorde provning med utmattningsbrott vid längre livstid och spänningsnivåer lägre än den traditionellt föreslagna "utmattningsgränsen". Nuförtiden används en indelning av utmattningsregimer i lågcykelutmattning (Low Cycle Fatigue LCF), högcykelutmattning (High Cycle Fatigue HCF) och utmattning vid mycket långa livslängder (Very High Cycle Fatigue VHCF). De huvudsakliga skälen till denna indelning är: i) behovet av säker design av komponenter, och ii) det faktum att brottmekanismerna är speciella i var och en av LCF-, HCF- och VHCF-regimerna. Det främsta målet med denna avhandling är att adressera utmattningsegenskaper hos höghållfasta verktygsstål. Med tanke på nya sammansättningar och produktionsmetoder i legeringsutvecklingen introduceras material av hög kvalitet kontinuerligt på marknaden; att förstå utmattningsresponsen hos dessa material är avgörande för potentiella användningar inom olika industrier och applikationer. Genereringen av experimentell utmattningsdata, analysen av de olika typerna av initieringsdefekter som hittats i varje material, såväl som undersökningen av utmattningsmekanismerna som uppstår under cyklisk belastning är huvudämnena som analyseras genom hela denna studie.

The welding process introduces residual stress originating from the heating, melting and cooling of the material. From the point of view of fatigue and stress corrosion cracking, the weld residual stress perpendicular to the weld axis is of particular interest. When qualifying weld parameters for welds in large cylinders having a ratio of radius to plate thickness larger than say approximately 100; reference to plane plates are often made for the sake of simplicity. However, the weld residual stress perpendicular to the weld axis is severely underestimated in the plane plate compared with the cylindrical structure. This observation is especially pronounced in connection with preheating. The source of the differences is probably due to the radial constraint of the cylinder, compared with that of a plane plate. A plane test specimen will underestimate the weld residual stress perpendicular to the weld axis in a cylinder, even if the radius of the cylinder is very large. However, a test specimen for an 8 m diameter cylinder with a plate thickness of 35 mm needs only to have a segment width of approximately 1.3 m to reflect the stress in the real structure. The weld residual stress perpendicular to the weld axis in the vicinity of the weld toe is governed by the depositing of the weld bead adjacent to the weld toe, neglecting the accumulated strain from the previous deposited weld beads in the multi-pass joint weld. Introducing tensile straining perpendicular to the weld axis during the entire welding procedure reduces the weld–induced residual stress after completed welding. The plastic zone of the weld area will be subjected to compressive strain after completed welding, which in turn will reduce the weld residual stress. This can be achieved by cooling the weld area, which in this case is not recommended since the material is sensitive to hydrogen cracking, or by pre-stretching or modifying the locations for preheating, all aimed to impose a tensile axial straining around the weld area during the entire welding process.

The use of extruded aluminium profiles in the vehicle industry is increasing. One type of aluminium extrusions in cars are crash boxes, which absorb energy at low-velocity crashes. To ensure the quality of the material, the crash boxes are tested through compression tests and tensile tests. The compression tests are costly with regards to both material and time but serve an important purpose; to allow an evaluation of the degree of cracking, which needs to be low. Based on an internal study by Hydro Extrusion Sweden AB in Finspång, whom this study is conducted in collaboration with, the purpose of this report is to correlate the results of compression- and tensile tests in order to in the future eliminate the need for compression tests. Five crash box profiles of alloy 6063 were extruded and treated with different quenching methods and ageing cycles. Through compression- and tensile testing, the alloy's properties were evaluated to find suitable ductility parameters that may be used to predict the cracking behaviour of a crash box depending on the ageing cycle. According to the internal study, it has been proven to work for a water-quenched 6063-alloy and using our results concluded that it is also possible with an air-cooled 6063-alloy. Furthermore, it is concluded that if the cracking behaviour of a crash box of the 6063-alloy is to be predicted, a proper model that takes the box’s geometry into account should be used. / Extruderade aluminiumprofiler blir allt vanligare inom fordonsindustrin. En typ av sådana aluminiumprofiler i bilar är krockboxar som tar upp energi vid låg hastighetskrockar. För att säkerställa materialets kvalitet testas krockboxarna med dragprov och kompressionstest. Dessa kompressionstest är material- och tidskrävande men de behövs för utvärdering av graden av sprickning som inte får vara för stor. Baserat på en intern studie vid Hydro Extrusion Sweden AB i Finspång, som detta projekt görs i samband med, är syftet med detta arbete att korrelera resultat från kompressionstest och dragprov för att på lång sikt kunna eliminera behovet av kompressionstest. Fem krockbox profiler av legeringen 6063 extruderades och behandlades med olika släckningsmetoder och åldringscykler. Genom kompressionstester och dragprov korrelerades legeringens egenskaper med varandraför att utvärdera lämplighet för duktilitetsparametrar som sedan undersöktes i syfte att kunna förutspå krockboxens sprickningsbeteende beroende på åldringscykel. Enligt den interna undersökningen har det påvisats att det fungerar med en vattenkyld 6063-legering och utifrån vårt resultat kan slutsatsen dras att det också fungerar för en luftkyld 6063-legering. Dessutom kan slutsatsen dras att om sprickbeteendet hos en krockbox av 6063-legering ska förutspås bör en modell som tar hänsyn till krockboxens geometri användas.

Precipitation modelling is interesting from both an academic and an industrial point of view. Such modelling tools may be used in the field of integrated computational materials engineering (ICME) for design and optimization of material properties. The aim of this thesis was to provide validation and further development of the model developed by Bonvalet et al (Acta Materialia 100, 2015, p. 169–177). The model was implemented in a Python code, which utilizes the TC-Python SDK from Thermo-Calc Software. Comparisons between the present work implementation and the commercial software module TC-PRISMA were carried out for precipitation simulations in a Fe–0.16 wt% C–4.0 wt% Cr alloy. Moreover, a systematic study of the influence of the interfacial energy and the number of nucleation sites on precipitation kinetics was performed. The results indicate that the present work model and TC-PRISMA calculate growth and coarsening of precipitates in a similar manner, but the models differ in how nucleation-related parameters are treated. Most significantly, the two models calculate the driving force in different ways. This causes the precipitation kinetics to be shifted in time between the two models. / Modellering av utskiljningsprocesser inom material är av både akademiskt och industriellt intresse. Verktyg och programvaror som modellerar utskiljning kan användas inom ett ICMEramverk (från engelska: integrated computational materials engineering) för att designa material med önskvärda egenskaper. Målet med detta examensarbete är att bepröva och fortsatt utveckla en urskiljningsmodell som presenterats av Bonvalet et al (Acta Materialia 100, 2015, s. 169–177). Modellen har implementerats i Python-kod, och koden har baserats på utvecklings-verktyget TC-Python SDK skapat av Thermo-Calc Software AB. Modellimplementeringen i Python har jämförts med det kommersiella programvarupaketet TCPRISMA genom simuleringar av urskiljning av karbider i en Fe-legering med 0,16 vikt% C och 4,0 vikt% Cr. Vidare har inverkan av ytenergi och antal kärnbildningspunkter på modellens resultat studerats. Sammantaget tyder resultaten på att modellen som implementerats och TCPRISMA beräknar tillväxt och förgrovning av karbiderna på snarlika sätt, men de två modellerna skiljer sig åt i hur de behandlar kärnbildningsparametrar. Den största skillnaden mellan modellerna är att den drivande kraften för kärnbildning beräknas på två olika sätt. Detta leder till att utskiljningsförfarandet förskjuts i tid mellan de två modellerna.

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Diamond-like carbon (DLC) is a versatile material which exhibits excellentmechanical, electrical and optical properties making it suitable for applications rangingfrom biomedical implants to engine components. The properties of DLC thin films aredetermined by the bonding configuration (sp3/sp2 fraction) of its carbon atoms. Inorder to prepare DLC thin films for desired applications, it is essential to control andestimate the sp3/sp2 fraction precisely. Raman spectroscopy is widely employed for the estimation of sp3/sp2 fraction due toits non-destructive nature, high probing depth and possibility of quick acquisition. Thequality of information obtained from Raman analysis depends largely on the structureof DLC thin films, which varies from one deposition method to another. Using theexisting approaches for the estimation of sp3/sp2 fraction for a particular type of DLCthin films could entail large errors and thereby result in misleading conclusions. For anaccurate analysis of the film structure, it is therefore important that a carefullydesigned strategy is employed. In this work, Raman spectroscopy is employed forstructural investigation of DLC thin films deposited by High Power ImpulseMagnetron Sputtering (HiPIMS). Owing to the unique DLC film properties obtainedfrom HiPIMS, Raman spectroscopic investigations were made by developing ananalysis routine relevant for HiPIMS-deposited films. The developed approach isvalidated by complementary analysis of film density. The method is further employedfor investigating the compressive stress and thermal stability of the resulting films. Theanalyzed films were deposited using different buffer gas (Ar and Ne) and ion energy toproduce a range of sp2/sp3 ratios. Raman measurements were performed using visible(532 nm) and UV (325 nm) lasers. Film density was determined using X-RayReflectivity (XRR) and chemical composition using Elastic Recoil Detection Analysis(ERDA). The compressive stresses of the films were determined usingwafer-curvature method and thermal stability of the films was investigated byperforming Raman measurements on films annealed from 100 degrees C to 600degrees C. By developing an analysis routine and employing appropriate fitting method, it wasshown that the Full Width at Half Maximum (FWHM) of the G peak in the Ramanspectrum is the most relevant parameter for estimating the sp3/sp2 fraction. Theaccuracy of the analysis routine was verified by studying the evolution of sp3/sp2fraction and film density with respect to ion energy. The correlation between sp3/sp2fraction and film density was good. The differences in mass density and compressivestresses between Ar- and Ne-HiPIMS deposited films were also found to beconsistent with the estimated sp3/sp2 fractions. The structural evolution of theannealed films, investigated by Raman spectroscopy, showed that the Ne-HiPIMS filmsexhibit a transition from sp3 rich structure to sp2 rich structure at ~450 degrees Cwhereas the transition for the Ar-HiPIMS films occurs at ~300 degrees C. This impliesthat the Ne-HiPIMS films are thermally more stable than the Ar-HiPIMS films.

Gångjärn i trä är ett sätt att utveckla och bidra till en hållbar möbelkultur och visa på trämaterialets stora möjligheter. Jag gör en omvärldsspaning kring användningen av trägångjärn; historiskt och i samtid, studerar trä och andra materials olika egenskaper samt tillverkar olika prover med trägångjärn varefter jag utför tester på dessa. Det har visat sig att hög precision på segmentens diameter är en avgörande faktor för en lyckad och effektiv tillverkningsprocess samt att placering av centrumstiftet har en påverkan på friktionen och är tillsammans med materialval det viktigaste att tänkta på för god slitstyrka och funktion över tid. Resultaten pekar också på att centrumstift av trä kan vara en bra ersättning till stål, att bivax är ett lämpligt friktionsminskande medium och att fisklim har klarat samtliga tester lika bra som ett PVAc-lim under samma förhållanden.

The global energy consumption is increasing and together with global warming from greenhouse gas emission, create the need for more environmental friendly energy production processes. Higher efficiency of biomass power plants can be achieved by increasing temperature and pressure in the boiler section and this would increase the generation of electricity along with the reduction in emission of greenhouse gases e.g. CO2. The power generation must also be flexible to be able to follow the demands of the energy market, this results in a need for cyclic operating conditions with alternating output and multiple start-ups and shut-downs. Because of the demands of flexibility, higher temperature and higher pressure in the boiler section of future biomass power plants, the demands on improved mechanical properties of the materials of these components are also increased. Properties like creep strength, thermomechanical fatigue resistance and high temperature corrosion resistance are critical for materials used in the next generation biomass power plants. Austenitic stainless steels are known to possess such good high temperature properties and are relatively cheap compared to the nickel-base alloys, which are already operating at high temperature cyclic conditions in other applications. The behaviour of austenitic stainless steels during these widened operating conditions are not yet fully understood. The aim of this licentiate thesis is to increase the knowledge of the mechanical behaviour at high temperature cyclic conditions for austenitic stainless steels. This is done by the use of thermomechanical fatigue- and creepfatigue testing at elevated temperatures. For safety reasons, the effect of prolonged service degradation is investigated by pre-ageing before mechanical testing. Microscopy is used to investigate the microstructural development and resulting damage behaviour of the austenitic stainless steels after testing. The results show that creep-fatigue interaction damage, creep damage and oxidation assisted cracking are present at high temperature cyclic conditions. In addition, simulated service degradation resulted in a detrimental embrittling effect due to the deterioration by the microstructural evolution.

The thesis work was made in cooperation with the I-EDDA project who evaluates the drill equipment used in core drilling. The aim of this work was to determine how and why the drill bits are worn. The work consisted of two parts; investigate drill bits used in field tests and develop a lab scale method to be able to change one drill parameter at a time and see how it affects the wear. During the field tests the rotational speed and the pressure on the drill bits were changed between the three boreholes drilled. In the lab test one parameter at a time was changed; the rotational speed, the water flow and the load. The lab test was developed to attempt to replicate the core drilling and was performed by pressing a piece of a drill bit against a rotating stone cylinder. The drill bits from the field tests and lab test were analysed with the same methods on both macro- and microscale for easier comparison. The results indicate that the lab scale test can be used to evaluate the wear of drill bits. The analyses show rock present on the matrix of all the drill bits, in various amounts. The load has the largest impact on the wear of the drill bits and cause a change in mechanism. A high pressure leads to a higher amount of damaged diamonds and three body abrasive wear on the matrix. Lower pressure leads to polished diamonds and erosive wear on the matrix.

Infiltration is used in the production of several different material groups as electric contact materials, copper infiltrated sintered steels and metal matrix composites. The mechanism of infiltration causes also unwanted difficulties in processing as brazing of porous sintered compacts. The common question, in this work has been, how is it possible to control infiltration in different materials processing techniques? In joining of powder metallurgically (P/M) produced porous compacts, by brazing, the inherent porosity of the compacts causes the melt filler metal to infiltrate the interconnected pore channels of the P/M parts, by capillary forces. This will result in high penetration depths and filler metal consumption and a limited amount of filler metal will be available for the joint. In the production of metal matrix composites (MMC:s), the difference in surface energies between the metallic and ceramic components prohibits a spontaneous infiltration of the metallic phase into the ceramic porous body. This work includes a general analyse of the different physical and mechanical methods to control infiltration in brazing of porous compacts and processing of MMC:s respectively. The experimental part of the work concentrates on the study of physical methods for the infiltration control. Brazing of porous sintered compacts has been studied experimentally through different thermal treatments. A special (Cu-Ni-Mn-Si) filler-metal, developed by others in order to facilitate alloying between iron in P/M- compacts and the elements in the filler-metal, has been used and the results has been studied by optical and scanning electron microscopy and the mechanical strength and hardness has been measured. In the work on MMC:s a method for processing of aluminium matrix-alumina reinforced composites by spontaneous infiltration has been studied by wetting and in- situ high temperature X-ray experiments. The investigation of brazing shows that the filler metal starts to melt already at 930 oC and a two phase alloy is developed in the joint. The diffusion of elements from the filler metal and the sintered compact causes a development of an alloy with high melting temperature in the surface area of the sintered compact that blocks the surface pores from continued infiltration. The wetting experiments show that the spontaneous infiltration in production of MMC:s is enabled by chemical reactions in the system concerned. The in-situ X-ray experiments show that the formation of magnesium-nitride appears below 600 oC. The formation of AlN as a second reaction product in the spontaneous infiltration has been detected for compact tested after a processing cycle with increased pressure of nitrogen- gas in the processing furnace. The in-situ X-ray study of the spontaneous infiltration has shown that the formation of magnesium nitride could be detected. The results show also that it is possible to study chemical reactions at and above the melting temperature of the metallic constituent of the system. The results show also that it would be possible to create alumina-aluminium MMC with different hardness levels. / Godkänd; 2004; 20070116 (haneit)