The thesis originates from a need to meet stricter environmental regulations for Scania, to reduce fuel consumption and emission from heavy-vehicles. Scania aims to fulfil these requirements by increasing combustion pressure and temperature. These conditions are tougher for the engine components and they shorten their lifetime. This thesis aims to improve Scania’s ability to increase the lifetime of a heavy-vehicle exhaust manifold, an engine component that collects exhaust from several engine cylinders into one pipe. This was done by conducting a material comparison and a parameter study, both used the FEM software Abaqus CAE. The material comparison consisted of three ferritic and austenitic ductile cast irons (SiMo51, SiMo1000 and Ni-resist) subjected to thermal stress. Their max stress was compared for two thermo-mechanical fatigue cases, out-of-phase and in-phase. A parameter study was also conducted to clarify the influence of thermal conductivity, thermalexpansion, Young’s modulus and yield strength on max stress for OP and IP in the exhaust manifold. The FEM simulation results from the parameter study were used to create functions that can be used to decide how to treat/process a material to minimise the stress in the exhaust manifold. They can also be used in material selection to choose a material that minimises stress. The research questions and their shortened answers can be seen below. 1. Which of SiMo51, SiMo1000 and Ni-resist produces the lowest tensile stresses? ForOP, SiMo1000 produced a slightly lower max principal stress than SiMo51. For IP, Ni-resistproduced the lowest max principal stress by a large margin. 2. How do different material properties affect the maximum stress during operation of thegiven component? Thermal conductivity has a decreasing relation to max stress. Thermalexpansion and Young’s modulus have a similar relation to max stress, stress increases forboth properties as they increase. A decreased yield strength decreases the max stress forstresses above the yield limit but has no effect on stress below it. 3. How should an objective function to minimise max stress in the component with regard to material properties be expressed? functions of OP and IP can be seen in the actual abstract.

<div>This research aims at investigating the direct in-situ synthesis of high-performance multi-component alloys such as high entropy alloys, bulk metallic glasses, and metal matrix composites using the directed energy deposition (DED) process, and modeling the entire solidification and microstructure evolution of these alloys via a novel three-dimensional cellular automata-phase field (3D CA-PF) model. These alloys are currently the focus of significant attention in the materials and engineering communities due to their superior material properties. In the 3D CA-PF model, the growth kinetics including the growth velocity and solute partition at the local solid/liquid interface is calculated by the multi-phase and multi-component PF component, and the 3D CA component uses the growth kinetics as inputs to calculate the dendrite morphology variation and composition redistribution for the entire domain, which could save the computational cost more than five orders of magnitude compared to the PF modeling that can only be applied to small domains due to its heavy computational requirements. Coupled with the temporal and spatial temperature history predicted by the experimentally validated DED model, this computation-efficient 3D CA-PF model can predict the microstructure evolution within the entire macro-scale depositions, which is known to be nonuniform due to the particular nature of additive manufacturing (AM) processes. </div><div>To achieve the final goal of direct in-situ synthesis of five-component CoCrFeCuNi high entropy alloys (HEA), and modeling of the solidification and microstructure evolution during the DED process, the proposed research is carried out in progressive stages with the increasing complexity of alloy systems. First, a simple binary material system of Ti-TiC composite was studied. The thermodynamically-consistent binary PF model is used to simulate the formation mechanism of detrimental resolidified dendritic TiCx. To capture the polycrystalline solidification, a grain index is introduced to link different crystallographic orientations for each grain. This PF model simulates the microstructure evolution of TiCx in different zones in the molten pool by combining the temperature history predicted by the DED model. The simulated results provide the solution of limiting the free carbon content in the melt, according to which, the formation of TiCx dendrites is successfully avoided by experimentally controlling the melting degree of premixed TiC particulates.</div><div>Second, the solidification, grain structure evolution, and phase transformation in the DED-built ternary Ti6Al4V alloy under the influences of thermal history are systematically simulated using the established simulation framework and a phase prediction model. The thermal history in a three-track deposition is simulated by the DED model. With such thermal information, the 3D CA model simulates the grain structure evolution on the macro-scale. The thermodynamically-consistent PF model predicts the local grain structure and concentration distributions of solutes Al and V on the micro-scale. The meso-scale CA-PF model captures the sub-grain microstructure evolution and concentration distributions of solutes within the entire molten pool. The dendritic morphology is captured within the large β grains. When the temperature drops below the β-transus temperature, the solid-state phase transformation of β→α/ is studied by the phase prediction model. Based on the predicted volume fractions of and α, the microhardness is also successfully assessed using rules of mixtures. </div><div>Third, the material system is expanded to a four-component ZrAlNiCu bulk metallic glass composite, whose raw composition is prepared by premixing the four pure elemental metals. The DED model is employed to obtain the temperature field and heating/cooling rates in single-track ZrAlNiCu bulk metallic glass composite, which provides insights for microstructure evolution. By delicate control of the material composition and utilization of the thermal history of the DED process, an amorphous-crystalline periodic structure is produced with in-situ formed crystalline particulates embedded in the amorphous matrix. This crack-free microstructure is successfully maintained within bulk parts, where a high fraction of the amorphous phase and crystalline phases are produced in the fusion zone and heat-affected zone, respectively. The large volume percentage of the amorphous phase contributed to the hardness, strength, and elastic modulus of the composite while the various soft crystalline phases improve the ductility by more than three times compared to monolithic metallic glasses. Nanoindentation tests are also performed to study the deformation behavior on the micron/sub-micron length scale. </div><div>Fourth, the material system is expanded to a five-component CoCrFeNiTi HEA alloy. Three CoCrFeNiTi HEA alloys with different compositions are designed and synthesized from premixed elemental powders via the DED process. Through a delicate design of composition and powder preparation, different microstructures are formed. H3-Co24.4Cr17.4Fe17.5Ni24.2Ti16.5 is mainly composed of a soft face-centered cubic (FCC)-γ phase while σ-FeCr, δ-NiTi2, and a small amount of Ni3Ti2 are precipitated and uniformed distributed in the FCC matrix for H1-Co22.2Cr16.1Fe19Ni21.8Ti20.9 and H2-Co25.9Cr15Fe17Ni20.8Ti21.3. With a large percent of the secondary phases, H1 exhibits a hardness value of about 853 HV0.5. These HEA alloys display a high oxidation resistance comparable to Inconel 625 superalloy. A detailed evaluation of the hardness, oxidation resistance, and wear resistance of these HEAs are conducted as compared with those of a reference HEA and two popular anti-wear steels.</div><div>Finally, a novel 3D Cellular Automata-Phase Field (CA-PF) model that can accurately predict the dendrite formation in a large domain, which combines a 3D CA model with a 1D PF component, is developed. In this integrated model, the PF component reformulated in a spherical coordinate is employed to accurately calculate the local growth kinetics including the growth velocity and solute partition at the solidification front while the 3D CA component uses the growth kinetics as inputs to update the dendritic morphology variation and composition redistribution throughout the entire domain. Taking advantage of the high efficiency of the CA model and the high fidelity of the PF model, the 3D CA-PF model saves the computational cost more than five orders of magnitude compared to the 3D PF models without losing much accuracy. By coupling the thermodynamic and kinetic calculations into the PF component, the CA-PF model is capable of handling the microstructure evolution of any complex multi-component alloys. Al-Cu binary alloys with 2 wt.% and 4 wt.% Cu are first used to validate the 3D CA-PF model against the Lipton-Glicksman-Kurz analytical model and a 3D PF model. Then, the 3D CA-PF model is applied to predicting the dendrite growth during large-scale solidification processes of directional solidification of Al-30wt.%Cu and laser welding of Al-Cu-Mg and Al-Si-Mg alloys. </div>

3D printing, also known as additive manufacturing (AM), has got rapidly developed since 1987. Compared with conventional manufacturing methods, 3D printing provides some advantages such as increasing material utilization and less waste of material. Maraging steel provides good strength and toughness without losing ductility, which has been used for the 3D printing technique. Selective laser melting (SLM) is one of the 3D printing methods, which is mostly used for metal and alloy powder. In this thesis, selective laser melting will be used for maraging steel. 3D printing maraging steel is a new material, the research about the properties of 3D printing maraging steel is still ongoing. Corrosion resistance is one of the most important properties of maraging steel due to the high cost of corrosion. So this thesis will focus on the corrosion behavior of 3D printing maraging steel. The purpose of this thesis was to find the best heat treatment condition for high corrosion resistance and to find the relationship between microstructure and corrosion behavior of maraging steel. In this thesis, several kinds of maraging steel samples with different heat treatment conditions were used. SLM, SLM austenized&amp;quenched, SLM aged, conventional austenized&amp;quenched, and conventional aged. Besides, two kinds of solutions were produced, NaOH (pH=11.5) and Na2SO4 (pH=6.5). To observe the microstructure, an optical microscope was used. The grain size is different between SLM and conventional samples, and also different between the samples with different heat treatment conditions. The potentiodynamic polarization method was used to measuring the corrosion behavior. SLM samples have much lower current density, and the passivation potential and the corrosion rate are similar compared with conventional samples. But due to the lack of further experiments, the relationship between corrosion behavior could be affected by the combined effect of several factors.

No description available.

AREVA NP Uddcomb AB wants to replace the material used for a specific valve seat used in boiling water reactors, BWR. Their solution is a weld overlay of different stainless steels composed of two buffer layers of the steel 309 MoL followed by two layers of the filler material SKWAM welded on type 316 stainless steel or carbon steel. The report focuses on the long term structural effects in the weld overlay due to the operating temperature in BWRs, in this case 270 °C. To investigate the thermodynamic stability in the weld overlay the computer software Thermo-Calc was used and a metallographic examination was carried out. The results from these procedures were compared and possible long term effects were discussed. Most likely spinodal decomposition is the most severe structural change that may appear in the material. At equilibrium conditions at the operating temperature ferrite is decomposed into Fe-rich and Cr-rich ferrite but since the kinetics is not included in the calculations it is not possible to determine the rate of decomposition.

The background to this bachelor thesis is an on-going project within the VINN Excellence Center Hero-m. The task in this thesis is to perform a literature survey about the martensite transformation and investigate how the resulting fraction depends on cooling below the Ms-temperature. Instead of calculating the undercooling for each of the known fractions of martensite the driving force will be evaluated. Several efforts have been made through the years to describe the relationships between fraction transformed austenite and temperature. The approaches to the first models were empirical and derived from collections of data regarding the amount of retained austenite at different quenching temperatures. Lately, studies have been made to derive a thermodynamical relationship using how the Gibbs energy is affected by increments in volume transformed austenite. Two equations are derived by calculating the resulting driving force at different known quenching temperatures and the respective percentage transformed martensite found in previous works. The data for the steels used show a characteristic slope when linearised. A trend for the steels which have a high characteristic slope is that they also have a high Ms temperature, and the steels which have a low characteristic slope tend to have a low Ms. Previous relationships which describe the martensitic transformation have considered the importance of the Ms temperature only in it being a starting temperature for the transformation. To further incorporate the Ms temperature in the equations presented, further research of the martensitic transformation is required. The approach in this thesis of using thermodynamically calculated data is a base for further investigation of the range of the martensite transformation.

The “475°C embrittlement” occurring in ferritic and duplex stainless steel is considered to be detrimental and it limits the application of ferritic and duplex stainless steel at elevated temperatures, i.e., above about 300°C . In this study, the effect from alloying elements Ni, Cu and Mn on 475°C embrittlement was examined based on microhardness measurement and Charpy V-notch tests as well as atom probe tomography (APT). It was found that, after aging for 10h, 3% Ni accelerates the ferrite decomposition dramatically, 5% Mn has minor effect and no effect of 1.5% Cu was seen. The hardness increase tested at 450°C and 500°C was consistent with the observations from APT. The embrittlement based on room temperature Charpy tests was observed mainly during the first 10h. The embrittlement in Fe-20Cr-3Ni alloy was attributed to ferrite decomposition, while the other three alloys may be influenced by other phenomenon as well. A clustering effect of Cu has been observed in Fe-20Cr-1.5Cu and it was supposed to contribute to the mechanical changes.

The influence of basicity, heat treatment as well as different oxygen partial pressures on the phase relationships in the CaO-MgO-SiO2-Cr2O3 slags was studied with a view to control the precipitation of Cr-spinel in the slag phase. The equilibrium phases in CaO-MgO-SiO2-Cr2O3 slag system in the range on 1673-1873 K have been investigated under low oxygen partial pressure as well as in as air atmosphere. In low oxygen partial pressure experiments, a suitable mixture of CO and CO2 was used to control the oxygen partial pressure. The oxygen partial pressure was kept at 10-4 Pa. The Cr2O3 and MgO contents in the slag were fixed to be 6 and 8wt% respectively. The basicity (CaO/ SiO2) of the slag was varied in the range 1.0-2.0. Gas/slag equilibrium technique was adopted to synthesize the slag at a suitable temperature above the liquidus point. One heat treatment procedure is that the samples were heated to and soaked at 1873 K for 24h in order to achieve the equilibrium state and subsequently quenched in water. The other is that the samples were heated to and soaked at 1873 K for 24h, then slow cooled to 1673 K and soaked at this temperature for additional 24h in order to achieve the equilibrium state at lower temperature before quenching in water. The chromium distribution and phase compositions in the quenched slag were studied using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction techniques (XRD). FACTsage software was used for the phase equilibrium calculations. The experimental results obtained from the present work are compared with the calculation results from FACTsage software as well as with results from samples directly quenched after soaking at 1873K. It is found that the spinel formation at 1873 K in air atmosphere is favored in the slag basicity range of 1.0 to 1.6. The size of spinel crystals increased drastically after slow cooling followed by annealing compared to samples being quenched after soaking at 1873 K. The amount of foreign elements dissolved in the spinel phase, and matrix phases decreased after slow cooling followed by annealing at lower temperature, resulting in purer phases with less defects. It was found that the amount of foreign elements in the spinel phase, and other phases decreased after soaking at very low PO2. The size of the spinel crystals was found to be larger in samples with low basicity. Spinel phase precipitation has improved in the samples with higher basicities compared to the results obtained in air. / QC 20111208

The production of metal powders by water atomisation is a well established process, which can be used to produce a wide range of particle sizes. A careful control of the particle size distribution is necessary, to atomise powders with a high quality and at a low production cost. Therefore, it is necessary to have a substantial knowledge of the relation between operational parameters and the particle size, to be able to produce water atomised metal powders with consistent and high yields. The main purpose with this thesis was to increase the knowledge about factors which affect the mass median particle size (d50) for water atomised metal powders. The specific objectives with the study were to develop a theoretical d50 model and to investigate the relation between the particle size and the physical properties of the liquid metal. Pilot scale experiments for liquid iron showed that alloy additions of carbon and sulphur decreased the d50 value, at a maintained liquid steel temperature before atomisation. Moreover, it was indicated that the reduced particle size at increased %C and %S contents may be related to a decreased viscosity and surface tension of the liquid metal, respectively. An alternative explanation could be that raised superheats at increased carbon contents increased the total available time for atomisation, which may have contributed to a reduction of the d50 value. The theoretical d50 model developed in this work showed a very good correlation to the current experimental data. The model considers the influence of surface tension, viscosity, melt stream diameter, water pressure, water jet angle and water to metal ratio. This model was further used to analyse how the d50 value was influenced by the viscosity and the surface tension. A reduced viscosity from 4∙9 to 2∙1 mPa s decreased the d50 value with 33%. In addition, the particle size was estimated to decrease with 21% by decreasing the surface tension from 1840 to 900 mN m-1. / Q 20120529

In this thesis work, some basic concepts about desulphurizationof hot metal have been done based on a literature study. Two experimentaltrials have also been carried out to study the slags: one consider as areference and in the other trial, the amount of calcium carbide was reduced by150 kg. The average carbide efficiency has been improved from 21.3% in trial 1 to 26.0% in trail 2. Metaldroplets containing iron oxides are found in three of eight heats and most ofmetal droplets are surrounded by Ti-compounds. The slags mainly consisted of (Ca,O, Si) and (Ca, S), with some low content of other elements.