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)

Godkänd; 1998; 20070404 (ysko)

<p>Godkänd; 1992; 20080407 (ysko)</p>

No description available.

The pressure has a major impact when it comes to control of chemical processes. A method for integrating electrical pressure sensors in high-pressure microfluidic chips has, however, so far not been developed and the aim of this project was therefore to study how capacitive pressure sensors could be designed and fabricated to measure pressures between 1-100 bar. Based on analytical calculations and simulations of the thickness and the deflection of the diaphragms, touch mode capacitive pressure sensors were designed, and the fabrication involved exploring both isotropic plasma etching with SF6 and wet etching using KOH to fabricate a diaphragm on a Si wafer. The method which was found to be most suitable was to etch the diaphragm by plasma etching with SF6, even though a pressure resistance of only 23.4 bar could be accomplished, which is believed to be a consequence of the surface roughness, resulting in an Ra-value of 0.43 µm. The surface roughness lead to that chips had to be assembled by aligning them with an IR-camera and glued together with UV-epoxy, which enabled low precision. A method which do not leave any large etching effects on the diaphragm’s surface is therefore recommended for future work, to both potentially increase the pressure resistance and enable chips to be anodically bonded.

No description available.

I mitt examensarbete undersöker jag hur jag som möbelsnickare och produktutvecklare kan bidra i en designprocess. I samarbete med arkitekt- och designkontoret Claesson Koivisto Rune har vi utvecklat en trästol från en första skiss till färdig produkt, där jag har fungerat som produktutvecklare hela vägen igenom designprocessen. Examensarbetet visar på produktutvecklarens roll i en designprocess. ”Från idén om en förenklad konstruktion och sammansättning till en produktionsfärdig trästol med perfekt sittkomfort. Endast tre grunddelar – ben, sits och ryggstöd som gör stolen till en stabil helhet. En alternativ designprocess utan inblandning av industriell produktutvecklingsavdelning.”

BaBibliography: pages 88-92. / A variety of ceramic and ultrahard materials have been subjected to both solid particle and cavitation erosion. The materials tested include three grain sizes of alumina, stabilised zirconias, sialon, cubic boron nitride and polycrystalline diamond, and these have a range of microstructural, physical and mechanical properties. The damage modes are described for the two types of erosion and the results are critically discussed. It has been shown that different properties and microstructural features control the respective types of erosion. Hardness is the critical property which controls material loss during solid particle erosion. Cavitation erosion in contrast is less sensitive to hardness, but is extremely defect sensitive and preferentially attacks weak or damaged regions on the target. Grain size and shape, and th.e properties of the grain boundary or intergranular phase exert a strong influence on both types of erosion. It has in addition been concluded, that a propensity for a stress induced phase transformation, such as that exhibited by stabilised zirconia, will benefit the resistance of a ceramic to erosion. Ultrahard materials generally outperform the structural ceramics that were tested. While it was not possible to ascertain the effects of grain size conclusively, a large extent of intergrowth between the crystallites during manufacture appears to be beneficial to erosion resistance.

The three boiling water reactors (BWR) in Oskarshamn produce about 10 % of the electrical power in Sweden. The combination of intense radiation fluxes and high temperatures in nuclear reactors creates an extraordinary environment. Therefore, a number of material challenges arise at a nuclear power plant that needs to be solved in order to maintain the nuclear power production, safety and reliability. Dissimilar metal welds can be found at a lot of places in nuclear power plants and due to reparations or replacement some dissimilar metal welds need to be welded on site. The technical regulations for the Swedish nuclear power plants specifies that welding of dissimilar joints shall be made with gap of at least 1.5 mm and in horizontal position. Welding a dissimilar joint on site makes it difficult to follow the technical regulations, therefore, the aim with this study is to determine if different welding positions of dissimilar metal welds affect the structure and composition of the weld metal in a negative way and to investigate the importance of a gap in the root. In this study six samples were welded in three different welding positions, horizontal, vertical and reversed vertical with or without a gap of 1.5 mm in the root. The samples were evaluated by non-destructive testing, optical microscopy, chemical analysis, tensile testing, bend testing and hardness measurements. The results shows that two of the samples welded without gap failed the transverse root bend test, the same samples did also have high hardness values in the root bead. The conclusions are that the welding position, horizontal, vertical or reversed vertical does not affect the weld negative in a noticeable way. However, the gap and a good dilution with the filler metal are important.

No description available.