The recycling of aluminium from used aluminium scrap leads to an unavoidable presence of pollutions in the form of elements of various amounts. Two such elements are iron and silicon. These will always be present to some extent in an aluminium alloy as they are introduced to the alloy during processing. Iron and silicon are accumulative elements, meaning that they can never be completely eliminated once introduced into the aluminium. Some alloys have very narrow compositional windows, they have strict regulations concerning amount of alloying elements allowed. This is of grave importance for the recycling process; to be able to produce specific alloys with limitations regarding content and mechanical properties. A project to uncover the effects of common elements in aluminium such as Mg, Si and Fe has been initiated by the industry. This work is closely related to the project and was carried out as a report during fall 2010 and continued as a master thesis during spring 2011. The aim of this work was to study the effects of variation of small amounts of iron and silicon in 4 different alloys of high and ultra high purity (>99.7 and >99.999 wt% Al, respectively). The main focus was to uncover the effect of the elements on mechanical properties. Tensile test experiments with specimens in uniaxial tension were conducted to uncover the mechanical properties of the alloys. In addition to the tensile tests other parameters like texture, particles, recrystallisation and micro structure development were investigated. DC-cast, extruded flat profiles and rolled and recrystallised versions of the 4 alloys were used during the work.The results from tensile tests performed on the rolled and recrystallised aluminium showed that an initial introduction of 0.066 wt % Fe and Si 0.068 wt % to an alloy containing no pollutions lead to a dramatic increase in strength properties (up to 100% for the tensile strength) and a mild decrease in elongation. The increased strength properties and reduced formability was traced to iron and silicon in solid solution. From the same tensile tests it was concluded that a further increase of iron and an introduction of a small amount of pollutions had close to no effect on the mechanical properties.

AbstractSteel alloys are the material that is most used in protective constructions today. The reason is the overall good properties of steels, with its high strength and hardness, high ductility, high formability and relatively low cost compared to other materials. Even though armour steels are affordable, work is done to limit expenses from production or come up with new and less expensive alloys.Case hardening is a technique for production of steel with a very hard and durable surface while still maintaining a tough and ductile core. Case hardened products have hard, durable and fatigue resistant surfaces and tough and durable cores. Case hardening is typically applied to machine parts that are exposed to heavy wear and high loads such as gears, bearings, screws and nuts, shafts, etcIn 2010, Lou et al. managed to significantly increase the penetration resistance of a low-cost steel (NVE36) by case hardening. Encouraged by this, Hans Magne Thorseth wrote his master’s thesis “Optimalisering av stål i beskyttelseskonstruksjoner” in 2010. His attempt to improve the ballistic strength of Hardox 450 steel by case hardening did not have the desired results. The ballistic limit velocity was reduced from approximately 800 m/s for the original Hardox 450 to approximately 770 m/s for the case hardened steel. The probable reasons for the reduction of the ballistic limit velocity was a too low carbon content increase from the carburizing and thus a too low hardness increase, in addition to deterioration of the metal core properties from the heat treatment. The objective of this master’s thesis was to improve the case hardening process used by Hans Magne Thorseth in his master’s thesis.The improvement work was divided into two parts, a preliminary project work and this master thesis. The project was carried out in the autumn of 2010, and the aim was to find the optimum case hardening process to produce steel with improved ballistic properties. This involved testing of different carburizing potentials to increase the surface carbon content of the metal and to find carburizing heat treatments that would retain the core properties of the carburized steel. Based on the results from the preliminary project it seemed possible to produce case hardened steel with surface hardness over 1000 HV, but a slight reduction of core hardness was difficult to avoid.The present master’s thesis was written during the spring of 2011. The key results from the preliminary project work were used to determine a range of case hardening courses. A total of 11 case hardening courses were tested, of which six courses employed carbon potential of 0.9% and five courses employed a carbon potential of 1.1%. Different hardening courses were tested, including direct hardening, a modified single hardening process and traditional and modified versions of double and triple hardening. Before the case hardening the plates were sandblasted to remove a corrosion-resistant primer that was applied to the plates. The primer was believed to limit the diffusion of carbon into the steel. In the preliminary project the primer was ground away and grinding was the preferred solution in this work as well, however, due to capacity issues sandblasting was employed.The ballistic limit velocity of the case hardened and the original Hardox 450 target plates were calculated from results obtained by ballistic experiments. The ballistic limit velocities of the case hardened samples, with approximately 787 m/s as the highest, were lower than that of the original Hardox 450, being approximately 800 m/s.Surface hardness measurements of the steel revealed a poor effect from the carburization, the hardest surface was measured at 735 HV. This could be explained by a probable surface decarburization of the original Hardox 450, which was discovered by microstructure examinations and hardness measurements. In contrary to in the preliminary project where this layer was ground away, the sandblasting did not remove the decarburized layer. Due to this, the case hardening did not have the desired effect on the steel surface, resulting in a too low surface hardness.The core hardness proved difficult to retain, the highest core hardness value obtained was below 460 HV, compared to the original Hardox 450 with core hardness of 475 HV. This could be another reason for the lower ballistic limit velocity of the carburized steel plates. However, the original Hardox 450 did not have the highest cross-sectional hardness integral value, so the ballistic properties probably also depend to some degree on ductility. A main reason for the superior ballistic limit velocity of the original Hardox 450 was therefore believed to be related to cracking of the rear side of the case hardened target plates during projectile penetration. The cracking seemed to be a result of the harder, and thus more brittle, outer surface layer.

Silicon is used in the production of various ceramic products. As the solar industry is advancing, the need for reusable crucibles for the casting of solar grade silicon has arisen. One idea is to produce silicon nitride crucibles by slip casting. During slip casting, silicon powder is mixed with water at high alkaline conditions to ensure good dispersion of the powder and a stabilized slip. This may lead to oxidation of the silicon and the evolution of hydrogen gas. The hydrogen evolution introduces porosity in the final product, thereby ruining the mechanical properties. Gaining knowledge on how to inhibit the oxidation of silicon in slurries would therefore prove valuable for producing defect-free silicon based ceramics.In this thesis the main objective is to gain knowledge about the oxidation of silicon in aqueous media, emphasizing on the formation of oxides with respect to initiation point, initiation time and characterizing of the oxide. Silicon powder and coarse silicon particles delivered by Elkem was oxidized in a purpose built apparatus. The effects on the powder and the coarse particles were examined by the several techniques, including among other: SEM, Colorimetry, HR ICP-MS and LECO. The mechanical properties of oxidized single crystal and polycrystalline silicon were also investigated, using nanoindentation.The most important results, indicates that the oxidation of silicon results in formation of silica and hydrogen gas evolution. Firstly silicic acid is formed until the solubility limit is reached. Further oxidation leads to silicic acid condensing to form; colloidal silica which adsorbs on the silicon particles and dispersed colloidal silica in the suspension. The oxide layer formation on the coarse silicon particles were studied and confirmed using SEM. The oxide is the result of silicic acid condensing to form silica and adsorbing on to the surface of the silicon. Initiation points for the oxidation were not found. A more controlled oxidation is needed and the study of the oxide layer must be performed with high resolution techniques like Atomic Force Microscopy and/or Auger Electron Spectroscopy.There were some problems related to reproducing the results with respect to the hydrogen evolution from the silicon powder. Storage of the powder seemed to be a key factor as the powder behaved differently from one week to another. Storage in a desiccator for two weeks lead to earlier and more intense hydrogen evolution. Any reasonable cause for this was not found, and is subject for further investigations. The initiation time for hydrogen evolution was therefore difficult to determine, as it is dependent on unknown parameters.Nanoindentation was found to be a useful technique for studying the mechanical properties of oxidized silicon. The results indicated that the single crystal samples were homogeneous with respect to mechanical properties, as each of the indents of the respective samples produced more or less the same value. The E-modulus for the oxidized single crystal sample was about 10 GPa lower than for the unoxidized sample, the hardness was not affected. The results for the polycrystalline sample is more difficult to interpret, but nanoindentation indicates that the oxidized sample is not as homogeneous as the single crystal particles with respect to mechanical properties. The hardness was equal to the single crystal samples, and the E-modulus was close to that of the unoxidized single crystal sample.

This master thesis has the objective to improve the mechanical properties of Super Duplex steel by adding Elkem Grain Refiner (EGR). EGR is commercial grain refiner where the active element is cerium. Cerium is a strong oxide and sulphide former whose inclusions are to act as sites for heterogeneous nucleation during casting. The cerium inclusions will form at low undercooling making it possible to grow equiaxed grains ahead of the solidifying front, reducing the size of the columnar zone normally seen in an ingot. By reducing the columnar zone the steel will have a larger zone of equiaxed, and smaller, grains improving the mechanical properties of the steel and reducing the segregation throughout the ingot. The experiment was performed with S4501 Super Duplex steel provided by Scana Steel Stavanger. The casting was done at Frekhaug stål, Bergen by adding 0.05, 0.075 and 0.1 wt% cerium to 120 kg casts. There were a total of 3 parallels, where 1 was cast at 1525ºC and 2 series at 1540ºC. The as cast structure was significantly refined, the columnar zone was reduced from 22 mm to being absent in the cast with most cerium added. The mechanical results show a linear increase in both yield and ultimate tensile strength with increasing amount of cerium. The elongation increased somewhat, but the impact toughness decreased linearly with increasing cerium content. The casting temperature did not seem to have an effect on the grain refining.

I denne rapporten er det tatt for seg modellering av mykningsreaksjoner etter deformasjon for AA1200- og AA3103-legeringer. Grunnleggende teori rundt mykningsreaksjonene for disse legeringene er presentert. Det er hentet inn eksperimentelle data for sammenlikning av modellerte data, og resultatene er presentert i form av grafer for flytspenning og tabeller for rekrystallisert kornstørrelse. Det er brukt to matematiske modeller som bakgrunn for simuleringene. Den ene, Alsoft, dekker mikrostrukturelle endringer, og den andre, Presipal, dekker presipitering under varmebehandling.Resultatene for flytspenninger viser at simulering av varmebehandlingsforløp for AA1200-legeringer gjøres enkelt ved hjelp av Alsoft på grunn av fravær av presipitering som har innvirkning på varmebehandlingsforløpet. Simulering for AA3103-legeringer er mer krevende på grunn av den bremsende kraften som utøves på rekrystalliserte kim og rekrystalliserte korn som vokser på grunn av samtidig presipitering under varmebehandling. Her viser resultatene at en direkte kobling av modellene Alsoft og Presipal gir akseptabel tilpasning mellom eksperimentelle data og simulerte data for flytspenninger.Modellering av kornstørrelser viser, ved en sammenlikning med eksperimentelle resultater, at modellen har endel utfordringer med hensyn til dette. Verken størrelser eller trend er i alle tilfeller realistiske. Dette kan skyldes usikkerhet i parametere som brukes.Konklusjonen av arbeidet er at modellene i seg selv fungerer, men det kreves endel arbeid rundt fastsetting av parametere for at disse skal være anvendelige. Per dags dato blir det mye synsing for at resultatene skal vise akseptable avvik i forhold til eksperimentelle data.

Cathodic protection is an effective corrosion protection for structures submerged in seawater. In addition to applying the current need to lower the metal below the protection potential, a resulting increase in interfacial pH leads to precipitation of calcareous deposit. This deposited layer act as a barrier against oxygen diffusion on the surface, hence lowering the current demand of the structure. However, this layer will also hinder the thermal conductivity, and is therefore unwanted at the surface of heat exchangers.There are several factors influencing the precipitation of calcareous deposit. This includes potential, current, pH, seawater chemistry, flow rate etc. These factors have been thoroughly investigated for many years, but mostly with steel as substrate material. Specimens of steel coated with thermal sprayed aluminum (AlMg5) and aluminum plates of alloys AA5082, AA1050 and Al99.99 were exposed to seawater for 5-6 weeks, polarized to -1050 mV vs Ag/AgCl. The current demand was constantly recorded using KorrosjonsLogger©. Results from introductory experiments are also included. The unsealed TSA specimens had the highest current demand, but were also exposed to a higher seawater temperature than the other specimens, which has influenced the results. The sealed TSA specimens had a current demand around 10 mA/m2 after 6 weeks, which is 10 times lower than usually found on steel specimens. For the aluminum plates the trend showed that the higher alloying elements, the higher current density.The explanation for the low current demand compared to steel is that the cathodic area for aluminum is the intermetallic particles that are cathodic to the matrix, while for steel the whole surface act as a cathodic site. In addition, mechanisms during cathodic protection of aluminum lead to an isolation of the cathodic particle, hence continuously lowering the current demand.After exposure, the specimens were investigated in SEM and the composition on the surface was found using EDS. The SEM images showed a furry surface on the TSA specimen, but no familiar structure of calcareous deposit, which has been seen on steel specimens. For the aluminum plates, the intermetallic particles had been “dug out”, showing a pit between the particle and matrix. A typical structure of calcareous deposit was not seen here either. However, the EDS analysis showed an increase in both Mg and Ca content. The Mg/Ca ratio varied over the surface, with the highest ratio and content for the intermetallic particles for the aluminum plates and at the peaks of the surface at the TSA specimens. The Mg/Ca ratios found were much higher than found on steel.Both the SEM images and EDS analysis confirms the theory that there will precipitate less calcareous deposit on TSA surfaces compared to steel. Further studies will show whether the small content found will have an influence on the thermal conductivity.

Due to recent fractures in grade 70 anchor chains in the fish farming industry, chain supplier Erling Haug AS has initiated an examination of a sandblasted anchor they sell today. The sandblasted anchor chain is of the same strength category as the chains associated with the mentioned accidents. The mechanical properties of the sandblasted chain were characterized in 2010 in a student project work[1]. The report expressed concern about the sandblasted grade 70 chains since the material fulfilled requirements to be susceptible to hydrogen induced stress cracking (HISC). Therefore, further research on the material was needed. Another grade 70 chain, of an unknown origin, was obtained to make a comparison. This chain had fractured in-service. It was therefore necessary to characterize the mechanical properties of the fractured chain before examining the two chain grades susceptibility to HISC. The fractured chain was examined in terms of its microstructure, hardness, transition temperature and strength. An attempt was made to explain why the fractured chain failed in-service.The tensile test of the fractured chain revealed that its yield strength was 140MPa lower than that of the sandblasted chain. It was considered possible that the fracture chain were weaker than they should have been and that the reason it failed in-service was due to overload.The susceptibility of the two chains to HISC was tested by submerging tensile specimens into a 3.5% NaCl solution in CorTest Proof rings, while exposed to hydrogen. Specimens were either hot dip galvanized (HDG), protected by an external potential of -1050mV vs. Ag/AgCl or freely exposed at their corrosion potential. Some specimens were pulled in steps till fracture, while others were held at a constant load for 14 days.Different loading and corrosion potentials were applied to the two chain qualities during the HISC test, but the experiment was unable to provoke brittle fractures in either of them. No cracking was observed in the SEMivfor any of the HDG tensile specimens. It was found that hydrogen have no influence the mechanical properties of the HDG tensile specimens, while hydrogen appear to assist in the development of cracks on the polarized specimens.

The objective was to investigate if the established theory concerning corrosion calculations and electrochemical behavior of carbon is valid when steel is exposed to AC in an electrolyte consisting of 3,5 wt% NaCl and distilled water. The experimental work was divided in two main parts. The first part concerned corrosion testing, including weight loss measurements in stagnant conditions in combination with linear polarization resistance experiments. AC-current densities investigated was 0-, 50-, 75-, 100-, 150-, 220- and 500 A/m2. Polarization curves were produced on two weight loss samples, one exposed to 150 A/m2 and the other exposed to 220 A/m2, at the end of the weight loss experiments.From the corrosion testing it was found that the estimated corrosion current densities (icorr) from the weight loss experiments on samples exposed to AC-current densities below 500 A/m2, was in an approximate accordance with the icorr values estimated from LPR. At 500 A/m2 the measured corrosion rates and corresponding corrosion currents were slightly higher than the remainder. The higher corrosion rate measured from the samples exposed to 500 A/m2 is suggested related to a non-faradaic corrosion contribution. The suggested mechanism is a facilitation of grain boundary corrosion at high AC-current densities leading to the loss of grains. This being a non-faradaic corrosion contribution it is not possible to measure with LPR or polarization curves. The constant B [mV] from the Stern-Geary equation was estimated on basis of LPR measurements. The constant displayed a decreasing trend with increasing AC-current densities. This was explained by the lowering of anodic and cathodic tafel slopes with increasing AC-current densities. The polarization resistance (Rp’ - [Ω∙m2]) also showed a decreasing trend with increased AC-current densities. This was explained by the increased current response in the LPR measurements with increasing AC-current densities.The second part was intended to elucidate the effect of AC on electrochemical behavior of the carbon steel through producing polarization curves at different AC-current densities using a rotating electrode experimental setup. Alterations in corrosion current densities, cathodic tafel slopes, limiting current density of oxygen reduction and corrosion potentials on steel without AC and at current densities of 100-, 150-, 220- and 500 A/m2 are investigated during the electrochemical testing.  From the rotating electrode experiments no significant change in corrosion current was found with increasing AC-current densities. The potential range, in which limiting current of oxygen reduction (ilim) appeared, decreased with increasing AC-current densities. This decrease in ilim also affected the corrosion potentials (Ecorr). A decrease in the potential range of ilim leads to a more cathodic Ecorr. A particular observation was found at AC-current densities of 150 A/m2 were the effect of ilim seemed absent. The samples exposed to this AC-current density also attained the most cathodic corrosion potentials at approximately -850mVSCE which was between 200-400mV lower than the samples exposed to the remaining AC-current densities. Cathodic tafel slopes showed a decreasing trend with increasing AC-current density. Anodic rafel slopes were considered absent due to pitting above Ecorr.Pictures of the weight loss samples were captured in the SEM. It was found that the formation of pits occurred on all weight loss samples exposed to AC. On the samples without induced AC no sign of pitting was observed. Hence it was found that the corrosion attacks attained a more local character when AC-current was induced in the steel samples.

This master’s thesis is based on experimental studies of the parameters influencing cold roll bonding (CRB) of the aluminum alloys AA1200 and AA3103,in the work hardened and annealed condition. The effect on the bond strength from the preparations parameters as degreasing agent, scratch brushing and exposure time for oxide growth is investigated in comparison to former studies. Further the effect of rolling speed and effect from contributing factors from the different testing methods is discussed. Three different methods for testing the bond strength are used. One of them was established during this study and was named Tensile Bond Strength Test (TBST). A final investigation of the fracture surfaces and bond interface in a scanning electron microscope (SEM) was carried out to analyze the bond mechanism and distribution of fractured oxides.The TBST is testing the direct bond strength with no peel or shear forces involved. It also only requires a fraction of the sample material for testing and any roll bonded sample is applicable for this test. These are the huge advantages with the test method. The test method is however still naive, and suffers from a series of challenges. The current test ranged is from 4MPa to 40MPa, but with potential for a large range expansion. Further are bond damaging effects, caused by the machining, reducing the accuracy of the measurements and compromising “grooving”; a measure taken for increasing the test range above 40MPa.The strain rate at which the samples were tested, showed to have strong influence on the measured bond strength. Much higher than the effect of any work hardening on either of the alloys. The preparation prior to roll bonding including an only 90s exposure time to air, ensures a very thin oxide layer and bonding at reductions down at 22.3%. Ductile “stretch lips” was found on the fracture surface, and run in direction normal to the rolling direction. The fraction of bonded surface area did not seem to follow the percent of reduction during roll bonding, which indicates a thinning of the oxide layer.

Zr70Ni16Cu6Al8 bulk metallic glass samples were cast and prepared for tensiletesting. Tensile tests were done at temperatures 77 K, 150 K and 295K, over a range of effective strain rates between 10−5 and 10−1/s in order toassess the dependence of plastic deformation through shear band sliding onthe aforementioned factors.A strong temperature dependence was found, with maximum shear bandsliding distance at 150 K. The sliding distance was also found to increasewith lowered strain rates. The temperature dependence is likely to stemfrom increased heat dissipation suppressing a decrease in viscosity, while thestrain rate dependence stems from a decrease in energy supply rate.Shear bands appeared at higher stresses at lower temperatures, resultingin larger elastic domains and higher ultimate tensile stresses. A mechanismwhere heat dissipation suppresses the formation of shear bands at low stresseswas proposed.v