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51	Welds in the lean duplex stainless steel LDX 2101 : effect of microstructure and weld oxide on corrosion properties Westin, Elin M. January 2008 (has links) <p>Duplex stainless steels are a very attractive alternative to austenitic grades due to their higher strength and good corrosion performance. The austenitic grades can often be welded autogenously, while the duplex grades normally require addition of filler metal. This is to counteract segregation of important alloying elements and to give sufficient austenite formation to prevent precipitation of chromium nitrides that could have a negative effect on impact toughness and pitting resistance. The corrosion performance of the recently-developed lean duplex stainless steel LDX 2101 is higher than that of 304 and can reach the level of 316. This thesis summarises pitting resistance tests performed on laser and gas tungsten arc (GTA) welded LDX 2101. It is shown here that this material can be autogenously welded, but additions of filler metal, nitrogen in the shielding gas and use of hybrid methods increases the austenite formation and the pitting resistance by further suppressing formation of chromium nitride precipitates in the weld metal. If the weld metal austenite formation is sufficient, the chromium nitride precipitates in the heat-affected zone (HAZ) could cause local pitting, however, this was not seen in this work. Instead, pitting occurred 1–3 mm from the fusion line, in the parent metal rather than in the high temperature HAZ (HTHAZ). This is suggested here to be controlled by the heat tint, and the effect of residual weld oxides on the pitting resistance is studied. The composition and the thickness of weld oxide formed on LDX 2101 and 2304 were determined using X-ray photoelectron spectroscopy (XPS). The heat tint on these lean duplex grades proved to contain significantly more manganese than what has been reported for standard austenitic stainless steels in the 300 series. A new approach on heat tint formation is consequently presented. Evaporation of material from the weld metal and subsequent deposition on the weld oxide are suggested to contribute to weld oxide formation. This is supported by element loss in LDX 2101 weld metal, and nitrogen additions to the GTA shielding gas further increase the evaporation.</p><p> </p> Duplex stainless steel welding weld metal HAZ nitrogen manganese austenite formation phase balance precipitates pitting resistance heat input solidification element loss evaporation deposition weld oxides discoloration mechanical properties thermo-mechanical simulation Geeble GTA laser LOM SEM EDS TEM Leco EPMA ferroxyl test XPS post weld cleaning pickling Materials science Teknisk materialvetenskap
52	Transmissionselektronenmikroskopische Untersuchungen zur Koausscheidung von Übergangselementen in kristallinem Silizium / Co-precipitation of transition metal impurities in crystalline silicon investigated by transmission electron microscopy Rudolf, Carsten 24 February 2009 (has links) No description available. 530 Physik Mathematics and Computer Science Silizium metallische Verunreinigungen Metallsilizidausscheidungen Elektronenmikroskopie ternäre Phasen silicon metal impurities metal silicide precipitates ternary phases electron microscopy 33.05 33.61 33.72 RPV 750: Elektronenmikroskopie {Physik} RDE 000: Experimentalphysik RVQ 000: Halbleiter {Physik}
53	Welds in the lean duplex stainless steel LDX 2101 : effect of microstructure and weld oxides on corrosion properties Westin, Elin M. January 2008 (has links) Duplex stainless steels are a very attractive alternative to austenitic grades due to their higher strength and good corrosion performance. The austenitic grades can often be welded autogenously, while the duplex grades normally require addition of filler metal. This is to counteract segregation of important alloying elements and to give sufficient austenite formation to prevent precipitation of chromium nitrides that could have a negative effect on impact toughness and pitting resistance. The corrosion performance of the recently-developed lean duplex stainless steel LDX 2101 is higher than that of 304 and can reach the level of 316. This thesis summarises pitting resistance tests performed on laser and gas tungsten arc (GTA) welded LDX 2101. It is shown here that this material can be autogenously welded, but additions of filler metal, nitrogen in the shielding gas and use of hybrid methods increases the austenite formation and the pitting resistance by further suppressing formation of chromium nitride precipitates in the weld metal. If the weld metal austenite formation is sufficient, the chromium nitride precipitates in the heat-affected zone (HAZ) could cause local pitting, however, this was not seen in this work. Instead, pitting occurred 1–3 mm from the fusion line, in the parent metal rather than in the high temperature HAZ (HTHAZ). This is suggested here to be controlled by the heat tint, and the effect of residual weld oxides on the pitting resistance is studied. The composition and the thickness of weld oxide formed on LDX 2101 and 2304 were determined using X-ray photoelectron spectroscopy (XPS). The heat tint on these lean duplex grades proved to contain significantly more manganese than what has been reported for standard austenitic stainless steels in the 300 series. A new approach on heat tint formation is consequently presented. Evaporation of material from the weld metal and subsequent deposition on the weld oxide are suggested to contribute to weld oxide formation. This is supported by element loss in LDX 2101 weld metal, and nitrogen additions to the GTA shielding gas further increase the evaporation. / QC 20101126 Duplex stainless steel welding weld metal HAZ nitrogen manganese austenite formation phase balance precipitates pitting resistance heat input solidification element loss evaporation deposition weld oxides discoloration mechanical properties thermo-mechanical simulation Geeble GTA laser LOM SEM EDS TEM Leco EPMA ferroxyl test XPS post weld cleaning pickling Materials Engineering Materialteknik
54	Microstructural and Micro-Mechanical Characterization of As-built and Heat-treated samples of HASTELLOY X produced by Laser Powder Bed Fusion Process Sanni, Onimisi January 2022 (has links) Microstructure and micro-mechanical characterization of as-built and heat-treated samples of Hastelloy X produced by laser powder bed fusion (LPBF) process has been carried out in this study. As-built LPBF blocks were solution heat-treated at 1177°C and 1220°C followed by fast cooling. The microstructure of as-built and heat-treated samples were studied by light optical microscopy, scanning electron microscopy, and electron backscatter diffraction. Instrumented indentation micro Vickers testing was performed to obtain microhardness and elastic modulus of asbuilt and heat-treated samples. Microtensile samples from as-built and heat-treated blocks were prepared and polished for mechanical characterization. Microtensile testing inside the scanning electron microscope was performed to evaluate the mechanical properties and to get information about the microstructural changes during plastic deformation. Microstructure characterization revealed disrupted epitaxial grain growth for the as-built samples whereas the two heated-treated Hastelloy X samples exhibited equiaxed grains with varying twin fractions. As-built Hastelloy X samples exhibited higher mean hardness than heat-treated samples. The yield strength of as-built samples reveals higher values as compared to conventional wrought Hastelloy X samples, whereas lower yield strength and higher elongation were observed for heat-treated samples as compared to as-built samples. Higher elongation and lower yield strength values were observed for the samples solution heat-treated at 1220°C compared to the solution heat-treated at 1177°C. Microstructural evaluation at different plastic strains during in-situ microtensile testing reveals a clear difference in dislocation density for as-built and heat-treated samples. As-built Hastelloy X blocks Laser powder bed fusion (LPBF) Solution heat-treatment Disrupted epitaxial growth Melt Pool Boundaries (MPB) Grain Boundaries (GB) Precipitates In-situ microtensile testing microhardness Mechanical properties Twin grain boundary fractions Bearbetnings-, yt- och fogningsteknik Metallurgy and Metallic Materials Metallurgi och metalliska material

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