Theoretical, physically-based models of fusion welding are developed, and calibrated using experimental data from practical welds. The following heat-affected zone phenomena are investigated: grain growth, precipitate dissolution and coarsening, martensite formation and hardness. A model is also developed to describe the effects of the welding arc and their dependence on welding conditions. All calculations are carried out using a microcomputer which readily allows the influence of a large number of material and welding variables to be taken into account. The results are presented as read-outs in the form of various types of Welding Process Diagrams, these providing information on weld geometry, H.A.Z. microstructure and hardness in a form understandable to the welding metallurgist and engineer alike. In addition, Implant Testing Diagrams are developed, based on similar modelling, which help to exactly locate the notch with respect to the grain growth zone and weld process. Diagrams can be constructed showing microstructural variation over a wide range of energy inputs corresponding to different welding processes, or for a particular process showing weld geometry and providing a physical picture of the weld. The programs are written such as to allow easy interaction between the operator and computer concerning choice of welding parameters, steel composition etc., and the storage of material data which can be readily called up by the operator. It is thus shown that the diagrams can be used to help optimize welding conditions, as well as supply information on the H.A.Z. microstructure and hardness. / Godkänd; 1984; 20070502 (ysko)

Deformation and stresses in butt-welding of plates were studied. The work includes numerical simulation and experimental verification. The simulations were performed by use of the finite element method. Temperature dependence of material properties and phase transformations were considered. A thermo-elastoplastic material model was used. Plane stress conditions were assumed. Automatic butt-welding of plates without backing needs close tolerances of joint geometry. The thermally induced deformations and stresses are of great importance for joint geometry during welding. Therefore the change of gap width in front of the moving arc has been of special interest in these studies. The residual stresses, which may affect inservice behaviour of welded plates, were also calculated and measured. The tack-welds were found to influence the change in gap width in front of the moving arc. A proper tack-welding procedure is important in order to avoid large changes in gap width during butt-welding. The tack-welds should be made as soon after each other as possible. The sequence in which the tack-welds are made also affect the change in gap width. The gap width increased during the last part of the butt-welding in the simulations performed in this work. This increase was larger for wide plates than for narrow plates. Residual stresses close to the weld were large. The effective stress reached the yield limit of the material in the weld line. / Godkänd; 1985; 20070424 (ysko)

Iron is one of the most important resources that can be found in the lithosphere; 90 % of all metal ores extracted are iron ore. Many steps are included in the extraction from iron ore to metallic iron, where the processes vary between different producers. Iron ore pellets, are a prepared burden material for ironmaking in the blast furnace. Such pellets are commonly sintered in a grate-kiln furnace system, where the kiln usually is insulated with mullite containing bricks. Different mechanisms wear these bricks and they need to be replaced regularly and this causes production stops. The slag present in the kiln consists of ~95 % hematite, alkali-, alkaline earth- and other oxides, mainly from pellets that have disintegrated and adheres in chunks on the bricks. This study is focusing on the interaction between refractories and slags that occurs in kilns during the sintering process in the iron ore pellet production. Results are shown from lab scale experiments, and from samples collected in industrial furnaces, commonly called rotary kilns. Slag/brick compatibility tests were performed in a laboratory furnace at various temperatures, holding times and atmospheres. Slag collected from a production kiln and three commercial bricks, in powder or solid form, were used. Deliberate additions of alkali species were included in order to evaluate their influence. XRD, DSC, TG and in-situ mass spectrometry confirm that addition of alkali dissolves the mullite in the bricks, and forms the phase nepheline (Na2O•Al2O3•2SiO2), which disintegrate to an amorphous phase at elevated temperature. QEMSCAN were used to view mineralogical mappings of different chemical phases by field image scans. It was found that when alkali penetrates the surface of the brick, besides formation of nepheline, phases as kalsilite (K2O•Al2O3•2SiO2), leucite (K2O•Al2O3•4SiO2) and potassium â-alumina (K2O•11Al2O3) are formed. Also seen is that potassium penetrates deeper, and in larger amounts than sodium in the lining material. Formations of alkali containing phases as the feldspathoid minerals kalsilite and nepheline are coupled to an expansion in the lining material, observed by dilatometry, causing structural spalling observed as cracks in some of the slag/brick compatibility tests. Grains of hematite with sizes between 50- 100 ìm stay on the original surface of the brick, while micrometer sized hematite migrates through the dissolved brick by capillary infiltration and diffusion, and nucleates in needle formations deeper in the lining material. We propose a wear mechanism of the bricks in an iron ore pellet producing kiln that involves these chemical reactions in combination with erosion by the continuously flowing slag. / Godkänd; 2008; 20081120 (ysko)

This licentiate thesis adds a new piece to the puzzle that describes how the microstructural characteristics influence the hardness behavior of a multilayer coating. It contains a presentation of the manufacturing and the subsequent characterization of multilayer thin films. These multilayers consist of alternating layers of crystalline titanium nitride (TiN) and amorphous silicon nitride (Si3N4), deposited with a physical vapor deposition technique referred to as reactive magnetron sputtering. The microstructure of as-deposited films was examined with cross-sectional transmission electron microscopy (XTEM) and x-ray diffraction (XRD). XRD studies revealed a transition in preferred orientation for TiN, from a pure 002 orientation to a mixed 111/002 orientation as the TiN layer thickness increased from 4.5 nm to 9.8 nm. XTEM studies showed a microstructure consisting of equiaxed or elongated TiN grains, depending on layer thickness, limited in size by the amorphous interlayers. Selected area diffraction verified the observed transition in preferred orientation in TiN. For small silicon nitride layer thicknesses (~0.3 nm) an epitaxial stabilization of Si3N4 to the crystalline TiN lattice was observed through high resolution electron microscopy studies. Instead of amorphous interlayers a cubic silicon nitride rich phase (SiNx) was observed. This is to the present knowledge of the author the first time this phenomenon has been observed within this material system. In order to explain the observed behavior a model based on the involved energies were developed. Nanoindentation was performed to evaluate the mechanical behavior of the coatings as the layer thicknesses varied. All multilayers were harder than the monolithic TiN film, which had a hardness of 18 GPa compared to 32 GPa for the hardest multilayer. An interesting observation was that the hardest multilayer corresponds to the presence of cubic silicon nitride. Curvature measurements were performed and showed that the residual stresses within the multilayers were compressive and relatively constant, 1.3±0.7 GPa. In addition to the XTEM studies of as-deposited samples, XTEM studies of deformed multilayers were also conducted. The 300 mN load produced plastic deformation in the substrate under the indent. Cracks within the multilayer normally propagated along TiN/Si3N4 interfaces, which suggest that a lower energy is needed for cracking along an interface compared to intralayer cracking. The observed hardness increase can be ascribed to the multilayered structure of these films. By the interruption of TiN growth with intermittent Si3N4 layers the produced microstructure consisted of small TiN grains, separated in the growth direction by amorphous or crystalline interlayers. Small grains are known to contribute to hardening, but the interlayers also contribute, acting as dislocation obstacles either due to the amorphous tissue or to coherency stresses. / Godkänd; 2004; 20060917 (cira)

Godkänd; 2008; 20081121 (ysko)

and the placement of the material. Hence, 3D printing can be an advantageous new method of constructing supercapacitors.In this thesis, the aim was to investigate how the different parameters of Electrohydrodynamic printing (EHD printing) will affect the spread of gold nanoparticles. The electrohydrodynamic printing method is a printing method that utilizes an electric field to cause droplet ejection from the nozzle. When the electric field exerts a force on the solution containing nanoparticles, it stretches the meniscus to a point where it becomes unstable and forms a droplet. EHD printing utilizes an electric field which gives the method a high spatial accuracy while being able to print droplets with within a separation distance of tens of nanometers.Different parameters were evaluated to achieve desired distribution of gold nanoparticles across a silicon wafer substrate. This thesis focuses on print speed, frequency, heat treatment and voltage, and how printing parameters affect the results. The results revealed a variation, while the printing patterns follow a trend. The best results achieved in this work came from a low nozzle-substrate voltage, high frequency, and high printing speed. The varying results could be brought on by variation in ink composition, the nozzle diameter, and the metal coating of the capillary, to name a few possible causes.Handledare:

Metastable stainless steels are promising engineering materials demonstrating good corrosion resistance and mechanical properties. Their mechanical properties are however significantly affected by the deformation induced martensitic transformation. Hence, in order to use these steels to their full potential it is vital to have profound knowledge on this martensitic phase transformation. The aim of this thesis was therefore to investigate the evolution of phase fractions, texture, microstrains and microstructure to improve the current understanding of the deformation induced martensitic transformation in AISI 301. To investigate the deformation behavior of AISI 301, in-situ high-energy x- ray diffraction during tensile loading has been performed on samples suffering different cold rolling reduction. Ex-situ transmission electron microscopy, electron back-scattered diffraction and optical microscopy were also used to characterize the microstructure at different deformation levels. The results show that parts of the austenite transforms to both ά- martensite and ε-martensite during deformation of AISI 301. The transformation behavior of ά-martensite is however completely different from the transformation behavior of ε-martensite. ε-martensite forms in a parabolic behavior, while the ά-martensite transformation can be divided in three characteristic stages. The third transformation stage of ά-martensite has previously not been reported and it is characterized by a series of rapid transformations, each of which is followed by a period of yielding without any transformation. Moreover, the lattice strain evolution in the austenite at high plastic strains was found to be oscillatory, which is correlated with the stepwise transformation of ά-martensite as well as changes in x-ray peak broadening. This behavior was also coupled with the evolution of microstructure, where a distinct banded structure consisting of slip bands and Ü-martensite was observed at low plastic strains. This banded structure was however broken at high plastic strains when the ά-martensite grew larger and formed a block- shaped morphology. These findings lead to the conclusion that the three stages of ά- martensite transformation is due to different stages of nucleation and growth. The ά-martensite will first form as small nucleus, mainly at dislocation pile-ups along slip bands. The nucleuses will grow moderately in size and the structure will become saturated with nucleuses. Hence, the only way more ά-martensite can form is by growth of the existing nucleuses. This growth is very localized and seen as bursts in the transformation curve. The oscillatory behavior observed for the lattice strains during martensite formation possibly originate when semicoherent boundaries between austenite and ά-martensite become incoherent as the ά-martensite grow large. / Godkänd; 2005; 20061213 (haneit)

Adhesive joints are used extensively in the automotive industry. There are many ongoing studies on the area of application of joining composite to other material using adhesive joints. In this study, an analysis of mechanical behaviour of composite single lap-joint (SLJ) for carbon fibre reinforced polymer (CFRP) assembled with steel is presented and the analyses are divided into three phases. The first phase consists of a parametric study on a SLJ using Volkersen analytical model (AM), which is the effect of adhesive thickness and overlap length of the SLJ under tensile load. It was found that with increasing the adhesive thickness the final peak load (strength of the joint) increases. The peak load also increases with increasing the overlap joint, but the limit value for the overlap length varies for different adhesive thickness. For example for the case of adhesive thickness of 0.5 mm, the curve reaches to its plateau with overlap length of 40 mm. It was also observed the increase of adhesive thickness leads to decrease of maximum shear stress at the edges of the single lap joint, but it increases as it approaches the middle of the overlap length. Phase two of this study consist of a shear stress comparison with the Volkersen AM with the finite element model (FEM) using ANSYS Parametric Design Language(APDL) software. The purpose of this comparison was to validate the AM. It was found that the AM has a good agreement with the numerical-model (NM). However, the shear stress from the AM at the edge is a little higher than the NM, this is because the analytical method only takes into account the shear stress in one direction but the NM also takes into account the normal shear stress in the other direction. Phase three of this study consists of an experimental analysis of SLJ mechanical behaviour due to the change in temperature of 180 degrees and change in adhesive thickness and also a comparison with the NM. Three adhesive thickness 1, 0.5 and 1.5 mm were tested. Different boundary conditions (BC), namely as with frame and fixed BC are tested for NM. The one with frame BC is to compare with experimental setup and the fixed BC is the equivalent to Volkersen’s geometry. Both experimental and numerical results, show that the relative deformation of the SLJ decreases with the increase of the adhesive thickness. Although the experimental values were much lower than the numerical one, they agree well with the numerical result in term of trend of relative deformation. In experimental analysis, it was found that increasing the adhesive thickness from 0.5 mm to 1.5 mm decrease the relative deformation from 7.8% to 5.3%. It was concluded that increasing the adhesive thickness decreases the stiffness of the joint and allows more thermal movement in the joint.

Godkänd; 1998; 20070404 (ysko)

The research described in the thesis concerns phase transformations and fatigue properties in the Ti-6Al-4V alloy. The need to weld the alloy for certain engine components can expose the alloy locally to non-optimum thermal cycles and it is therefore of importance to gain an understanding of the kinetics involved in the phase transformations during heating and cooling. Moreover, for the purpose of modelling and computer simulations of heat treatments and welding processes, quantitative descriptions of the transformation are necessary. One focus in this work has been to examine the feasibility of using high temperature X-ray diffraction (HT-XRD) to study the phase transformation kinetics. In addition, two components of Ti- 6Al-4V produced by ring-rolling and closed die forging, respectively, showed unexpected differences in low cycle fatigue (LCF) under certain loading conditions. Quantitative metallographic studies and texture examinations were conducted in order to find possibly reasons for the observed difference in fatigue properties. The HT-XRD technique was successfully used to monitor the alpha-to-beta transition during heating and the beta-to-alpha transition during cooling and including the transformation kinetics during isothermal hold. From the recorded spectra the thermal expansion properties for the alpha and beta phases could be extracted up to a temperature of 1050°C, enabling the determination of the overall thermal expansion for the alloy by using rule of mixture (ROM) calculations. Quantitative metallographic studies revealed that the closed die forged material exhibited a finer primary alpha grain size and a finer Widmanstätten platelet colony size which would be expected to provide a superior resistance to fatigue crack initiation. Observed differences in the texture of the two materials as determined by electron back-scattered diffraction might also have contributed to the difference in fatigue properties. / Godkänd; 2002; 20070224 (ysko)