This thesis covers reduction-annealing synthesis of nanostructured SiC-TiCN and SiC-TiC particulate composite powders. These were characterized by X-ray diffraction and electron microscopy. In the SiC-TiC powder it was found that TiC could be added in certain amounts by reducing controlled amounts of titanium chloride source followed by a suitable annealing. A transmission electron microscopy showed that TiC formed polyhedrons and SiC formed rods. This was in agreement with a trend towards these crystal shapes, regardless of synthesis method, as found in the literature. In the SiC-TiCN particulate powder, nitration was achieved at low nitrogen concentration. In a scanning electron microscopy study it was seen that SiC formed elongated crystals, while TiCN formed polyhedrons. A gradual nitration of TiC into TiCN was proposed. Nitration was promoted by a high reactivity of TiC and an integrated nitrogen surplus over titanium and carbon amount during annealing.

Manufacturing simulations is today on a level where a manufacturingchain can be simulated including various steps such as machining, welding, metal deposition and heat treatment. This opens up for the possibility to investigate different manufacturing routes without the high costsof experimental work. In the case of welding and metal deposition theeffect of fixtures and ordering of weld sequences can be evaluated withrespect to deformation and residual stress. If a heated tool is included ina hot forming simulation there is a possibility to find process parameters that produces the desired microstructure in the sheet metal component.The work in this thesis has focused on techniques for increased effi-ciency in the context of large and complex structures and also alleviatingthe work during model definition for metal deposition and Joule heating.

In hot rolled steel strip production the processed material are after the cooling section coiled into coils. Coils do normally weigh around 20 tons with a diameter of 2 m and heights equal to the strip width e.g. 0.8-1.4m. When processing HSLA (High Strength Low Alloy) steel grades the initial/coiling temperature is about 650°C but to achieve the full strength enhancement potential from the subsequent precipitation hardening the cooling history is crucial to control. A too high cooling rate will disable diffusion of alloying elements before the destined material properties have been achieved. This may result in downgraded or in worst case even scraped material. Having comprehensive knowledge of the thermal history is essential in controlling coiled material properties and in understanding root-causes for different mechanisms. A 2D thermo-mechanical FE model has in this licentiate work been developed to predict the transient temperature distribution as a function of position and stress state in coils when cooling. The model accounts for the imperfect and pressure dependent contact conditions between adjacent laps that cause anisotropic thermal properties in radial and axial directions. The imperfect contact is in a macroscopic level caused by oxide, dust, water and strip shape properties inherited from up-stream processes and in a microscopic level by surface conditions like roughness and slope of asperities etc. The stresses formed under coiling and cooling has a strong influence on the contact conditions and the thermal heat conductive properties in radial direction. In this model the total stress state during cooling is approximated as a combination of initial stresses set by the coiler and the thermally induced stresses caused by thermal gradients.The thermo-mechanical model developed and explained in this licentiate thesis has proven to be able to predict the thermal cooling of coils with good agreement in comparison with the performed measurements campaigns. Furthermore does the model form an accurate platform to be used in a continuing work for further investigations where the thermal trajectory and stresses have an influence e.g. on coil-set effects as length and cross bow or mechanical properties.

Ductile fracture presents challenges with respect to material modelling and numerical simulations of localization. The strain and damage localization may be unwanted as it indicates a failure in the process or, as in the case of machining and cutting, a wanted phenomenon to be controlled. The latter requires a higher accuracy regarding the modelling of the underlying coupled plastic and fracturing/damage behaviour of the material, metal in the current context as well as the robustness of the simulation procedure. The focus of this thesis is on efficient and reliable finite element solution of the localization problem through the non-local damage model. The non-local damage model extends the standard continuum mechanics theory by using non-local continuum theory in order to achieve mesh independent results when simulating fracture or shear localization. In this work, the non-local damage model and its various simplifications are evaluated in an in-house finite element code developed using Matlab™. The accuracy, robustness, efficiency and costs of the models are investigated and also compared to a general multi-length scale finite element formulation. A numerical study versus published data is used to demonstrate the validity of the model. The explicit non-local damage variant will be implemented in a commercial finite element code for use in machining simulation

Composites of 3 mol% yttria-doped tetragonal zirconia (3Y-TZP) reinforced with multiwalled carbon nanotubes (MWCNT) up to 2 wt% have been produced using spark plasma sintering (SPS). The theoretical densities of the studied composites were found to be between 99.4 and 97.4 %. The average grain size of the composites was decreasing with addition of MWCNT content from 174 to 148 nm. The effect of MWCNTs on the mechanical properties of 3Y-TZP has been investigated. A novel method was used for the calculation of the true fracture toughness and reported for the first time in this type of composites. It was based on producing a shallow surface sharp notch machined by ultra-short pulsed laser ablation on single edge V-notch beam specimens. Indentation fracture toughness was measured using Vickers indentation and it was found to be increasing with the addition of MWCNT content while the true fracture toughness is hardly increasing. It was concluded that the increase in the resistance to indentation cracking of the composites cannot be associated to higher true fracture toughness. Moreover, nanoindentation was measured using Berkovich nanoindenter where the contact hardness and elastic modulus were determined by Oliver-Pharr method. It was found that both properties decrease with the addition of MWCNTs.Additionally, the effect of MWCNT on the tribological properties of 3Y-TZP was also investigated. The friction coefficient (COF) was studied by performing nano- and macro-scratches using diamond Berkovich and Rockwell indenters, respectively. Furthermore, the COF and the wear rate were determined in reciprocating sliding where a zirconia ball was used as a counterpart under dry conditions using a load of 5 N and sliding distance of 100 m. The COF was found to be decreasing with increasing MWCNT content. However, in macro-scratch testing, there was a critical load over which brittle fracture sets in and its value decreases as the MWCNT content increases. The wear resistance was found to be decreasing slightly for less than 1 wt% MWCNT, while it increased strongly for the addition of 2 wt. % MWCNT under the conditions studied.

The present thesis deals with characterization of silicate structures with a determined morphology and structure such as ordered mesoporous silica and layered silicates. Mesoporous silica groups are amorphous solids exhibiting highly ordered pore structures with narrow pore size distributions and large surface areas. Porous materials are used in various applications such as in adsorption, separation, removal of pollution treatments, molds for templating, etc.Another interesting group of layered materials are crystal silicates with minerals of natural origin. The silicates have a structure that consists of staked layers in which planes of oxygen atoms coordinate to cations such as Si4+, Al3+, Mg2+, Fe3+ to form two dimensional sheets. The coordination of cations in adjacent sheets typically alternates between tetrahedral and octahedral. The properties and uses of the clays vary widely due to the differences in their structure and composition. Some important applications are paints, adsorption, intercalation, removal of pollutants from water and in ceramic industry.The thesis consists of two parts. In the first study characterization of synthesized and functionalized ordered mesoporous silica were performed. Mesoporous silica with a large surface area on which organic functional groups are grafted was used to synthesize cobalt nanoparticles. Investigation by SEM and TEM showed hexagonal particles, with a pore size about 10 nm. The functionalization of the silica was studied by FTIR and TG/DTA techniques and the obtained nanoparticles were characterized by XRD, TEM and EDX analysis. In the second study, an extended literature review on properties of clays is presented. Samples from three different clay deposits, Ivirgarzama (IC), Entre Rios (EC) and Uspha-Uspha (U) from Bolivia were characterized by different experimental techniques in order to assess their relevant features. The chemical and mineralogical analysis showed that the clays consist mainly of kaolinite and illite along with quartz in different amounts. Also, certain amounts of feldspar, iron and magnesium are present in the clays and with predominance in the EC clay. Thermal analysis (DSC/TG and dilatometer) and XRD were used to study the phase transformations and their microstructural evolution at sintering. The EC clay with a high alkali and iron content influenced both the onset of liquid formation and the onset of sintering. Mullite is a crystalline phase that strengthens the ceramics and it was formed in all the studied clays. Based on these results, the EC and U clays provide required characteristics that enable them for use in the fabrication of products with red tonality, especially bricks, roofing tiles and rustic floor tiles. The IC clay with relatively low iron content and with relatively good refractoriness can be used for production of firebricks and also for partially replacing kaolin and silica in white firing ceramics. Thus, the clays from Ivirgarzama, Entre Rios and Uspha-Uspha are promising raw materials and they should be considered as valuable resources for the production of building ceramics.

In recent years steels containing Si contents of 1,5% or more have been isothermally transformed in order to obtain a microstructure consisting of bainitic ferrite laths and retained austenite. The refined microstructure and presence of retained austenite has allowed the manufacture of steels with high tensile strength and considerable elongation. The work in this thesis is motivated by the need for more knowledge, especially regarding wear and fatigue properties before they can be used in engineering applications.In this work the rolling-sliding wear resistance and fatigue strength of ausferritic (carbide free bainitic) steels have been investigated. The dry rolling-sliding tribological behavior of 60SiCr7 steel, with 1.65% of Si was investigated in austempered conditions. The obtained ausferritic microstructure contained laths in the sub-micron range. It was found that the retained austenite content decreased and the hardness increased with lower austempering temperatures, and these changes resulted in decreasing the wear rate.The wear behavior of nano-structured ausferritic steels was investigated using the same rolling-sliding conditions as the previous study. If steels of the same hardness are compared, the wear rate was reduced by half in nano-structured steels in relation with the results obtained previously for the 60SiCr7 steel. Initial hardness was an important property in reducing rolling-sliding wear. Surface hardness after wear was inversely proportional to the wear rate. It was found that the increased plasticity obtained from the transformation of retained austenite into martensite (TRIP effect), present in these steels can be beneficial for the wear resistance.The effect of austempering 55Si7 spring steel on its fatigue strength was also investigated. Three heat treatments were done, isothermal transformation at 300 and 350°C respectively and quenching and tempering at 460°C. The samples were tested in rotating-bending fatigue. It was found that by austempering at 300°C the endurance limit was improved by approximately 25% in comparison with the other two heat treatments. The improved fatigue life was mainly due to the carbide-free microstructure. The transformation of austenite into martensite improves fatigue strength, but this depends on the stability of the retained austenite. With the current work some insight has been gained on the behavior of carbide-free bainitic steels in wear and fatigue. The future work will include high resolution techniques in order to further investigate in-depth both the wear and fatigue mechanisms. In addition, other wear modes will be investigated, particularly pure sliding.

The multiresolution continuum theory is a higher order continuum theory where additional kinematic variables are added to account for the microstructural inhomogeneities at several distinct length scales. This can be particularly important for localization problems. The strength of this theory is that it can account for details in the microstructure of a material without using an extremely fine mesh. The thesis focuses on implementation and verification of a 3D elastic-plastic multiresolution element based on an implicit time stepping algorithm. It is implemented in the general purpose finite element program FEAP. The mesh independence associated with the length scale parameter is examined and the convergence rate of the element is also evaluated.

Titanium and its alloys are attractive engineering materials in aerospace industry because of their outstanding mechanical properties such as high specific strength and excellent corrosion resistance. Ti–6Al–2Sn–4Zr–2Mo (Ti–6242) and Ti–6Al–4V (Ti–64) are two alloys commonly used for manufacturing components in jet engines, such as fan blades, disks, wheels and sections of the compressor where the maximum temperature is in the range of 300–450 °C. At temperatures above 500 °C and in oxygen containing environments, these alloys are oxidizing rapidly. Oxidation normally involves formation of an oxide scale on top of the metal and a hard and brittle oxygen enriched layer beneath the scale which is known as “alpha–case”. The alpha–case layer has a detrimental effect on important mechanical properties such as ductility, fracture toughness and especially the fatigue life when an engine component is subjected to dynamic loading. In order to increase the understanding of the oxidation and alpha–case phenomena, the behaviour of these two alloys after long time exposure in air at elevated temperature has been investigated. Heat treatments were performed on Ti–6242 and Ti–64 alloys in ambient air at 500, 593 and 700 °C for times up to 500 hours. The oxide scale and the alpha–case layer were analysed, characterized and compared for both alloys. It was found that the oxide scale and alpha–case thickness are functions of temperature and time. Faster and more complex oxidation kinetics was noted in Ti–64, whereas in Ti–6242 the oxidation kinetics was found moderate at all tested temperatures and times. Discrepancies in the oxidation kinetics are believed to be because of the differences in the chemical composition and the microstructure of the two alloys. In addition, different morphology of the oxide scales was observed after 500 hours exposure time at 700 °C. The thickness of the alpha–case layer was measured using conventional metallographic and microscopic techniques. It was found that in both alloys the alpha–case growth obeys parabolic law with respect to time at all three tested temperatures. In addition, the diffusion coefficients and the activation energy of oxygen diffusion were estimated in the temperature range of 500–700 °C for the two alloys. Electron probe micro analyser (EPMA) was used to measure the oxygen concentration along the thickness of the alpha–case layer. It was found that the oxygen concentration decreases along the alpha–case layer. The oxygen concentration profiles were used to estimate the alpha–case thicknesses and it was found good agreement with the optically measured values for almost all investigated temperatures and times. Only at 700 °C in the time interval 300–500 hours in Ti–6242 a difference between the results from the two methods was found. Moreover, the EPMA concentration profiles of the main α and β alloying elements, before and after heat treatment at 700 °C for 500 hours, revealed microstructural changes and an increase of the α–phase volume fraction in the two investigated alloys.

Simulation based design enables rapid development of products with increased customer value in terms of accessibility, quality, productivity and profitability. However simulation of metal cutting is complex both in terms of numeric and physics. The work piece material undergoes severe deformations. The material model must therefore be able to accurately predict the deformation behavior for a large range of strain, strain rates (>50000 s-1) and temperatures. There exist a large number of different material models. They can be divided into empirical and physically based models. The far most common model used in simulation of metal cutting is the empirical Johnson-Cook plasticity model, JC model. Physically based models are based on the knowledge of the underlying physical phenomena and are expected to have larger domain of validity. Experimental measurements have been carried out in order to calibrate and validate a physical based material model utilizing dislocation density (DD) as internal variable. Split-Hopkinson tests have been performed in order to characterize the material behavior of SANMAC 316L at high strain rates. The DD model has been calibrated in earlier work by Lindgren et al. based on strain rate up to 10 s-1 and temperatures up to 1300 °C with good agreement over the range of calibration. Same good correspondence was not obtained when the model was extrapolated to high strain rate response curves from the dynamic Split-Hopkinson tests. These results indicate that new deformation mechanisms are entering. Repeating the calibration procedure for the empirical JC model shows that it can only describe the material behavior over a much more limited range. A recalibrated DD model, using varying obstacle strength at different temperatures, was used in simulation of machining. It was implemented in an implicit and an explicit finite element code.Simulation of orthogonal cutting has been performed with JC model and DD model using an updated Lagrangian formulation and an implicit time stepping logic. An isotropic hardening formulation was used in this case. The results showed that the cutting forces were slightly better predicted by the DD model. Largest error was 16 % compared to 20 % by the JC model. The predicted chip morphology was also better with the DD model but far from acceptable. Orthogonal cutting was simulated using an updated Lagrangian formulation with an explicit time integration scheme. In this case were two hardening rules tested, isotropic hardening and a mixed isotropic-kinematic hardening. The later showed an improvement regarding the feed force prediction. A deviation of less than 8% could be noticed except for the feed force at a cutting speed of 100 m/min. The time stepping procedure in combination with the mesh refinement seems to be able to capture the chip segmentation quite well without including damage evolution in the material model.Further works will mainly focus on improving the DD-model by introducing relevant physics for high strain rates.