Quaternary cubic (TixCr1 − xAl~ 0.60)1 N1 coatings with 0 &lt; x &lt; 0.33 have been grown using reactive cathodic arc evaporation. When adding Ti the hardness was retained after annealing up to 1100 °C which is a dramatic improvement compared to CrAlN coatings. The coatings showed an age hardening process caused by spinodal decomposition into coherent TiCr- and Al-rich cubic TiCrAlN domains and the formation of hexagonal AlN precipitates and cubic TiCrN domains in the vicinity of the grain boundaries. The improved hardness was attributed to the stabilization of the cubic structure suppressing the formation and growth of hexagonal AlN. Furthermore, the presence of Ti atoms generated incoherent nanometer-sized crystallites within the hexagonal AlN precipitates disrupting the hexagonal lattice during the coarsening process. The addition of Ti promoted the formation of a TiO2 layer over Al2O3 resulting in a lower oxidation resistance. However, by tuning the composition it is possible to design coatings to have both good oxidation resistance and good high temperature mechanical stability. / <p>Funding Agencies|SSF project Designed multicomponent coatings, MultiFilms||</p>

Bulk forming and cutting are widely used to shape metals in industrial production. Bulk forming is characterized by large strains, extensive plastic deformation and large surface expansions. Cutting is characterized by high speeds, high pressures and high temperatures. The prevailing conditions during these processes lead to transfer of work material to tools. In bulk forming this is a significant problem. The transferred work material is hardened and becomes harder than the work material, causing galling. This leads to high friction and high forming forces, bad surface finish of the formed products and significant difficulties to produce complicated geometries. In cutting, transfer of work material can be desired for protection of the tool surface. However, the transfer film has to be of the correct type to provide a stable and predictive behaviour during operation. In this thesis the influence from tool material and surface treatment on work material transfer has been studied for both applications, with the use of simplified laboratory test methods followed by extensive surface studies. Both the tendency to, appearance of and chemical composition of work material transfer is evaluated. The results are compared with real industrial examples, to ensure that the correct mechanisms are mimicked. In forming, the problems arise when poor lubrication prevails, due to high forming forces or large surface expansions. The transfer of work material can then be avoided with the use of a galling resistant coating, offering low adhesion. However, the coating has to be as smooth as possible, to avoid activation of the work material and subsequent transfer. In cutting, the desired transfer film can be obtained by choosing the correct cutting parameters. The geometry and material of the fabricated component is often predetermined, setting the general cutting conditions, but the cutting speed influences the formation of the transfer film. Too low speed or too high speed leads to an unstable cutting process and poor surface finish of the piece. The speed intervals for each mechanism are partly determined by the tool material and thus by the tool coating.

Yttria Partially Stabilized Zirconia (Y-PSZ) plasma-sprayed coatings are widely used in turbine engines as thermal barrier coatings. However, in diesel engines Y-PSZ TBCs have not met with wide success. To reach the desirable temperature of 850-900˚C in the combustion chamber from the current temperature of 400-600˚C, a coating with a thickness of approximately 1mm is required. This introduces different considerations than in the case of turbine blade coatings, which are on the order of 100µm thick. Of the many factors affecting the durability and failure mechanism of TBCs, in service and residual stresses play an especially important role as the thickness of the coating increases. For decreasing the residual stress in the system, a multi-layer coating is helpful. The design of a multilayer coating employing relatively low cost materials with complementary thermal properties is described. Numerical models were used to describe the residual stress after deposition and under operating conditions for a multilayer coating that exhibited the desired temperature gradient. Results showed that the multilayer coating had a lower maximum stress under service conditions than a conventional Y-PSZ coating. Model validation with experiments showed a good match between the two.

With increasing attention paid to metal-supported SOFCs recently, metal supports have become important factors in the performance of the cells. The formation of surface oxides and the poisoning of Cr from Cr2O3-forming metal supports often result in the degradation of the cells. However, few studies have focused on developing oxidation resistance and decreasing Cr migration from porous alloys in intermediate temperature metal-supported SOFCs. In this work, Y2O3 and CeO2 coatings were applied to porous AISI 430 stainless steels by sol-gel dip coating. Phases and microstructures of the coatings on the porous metal supports were characterized by XRD and SEM with EDS, respectively. The effects of the coatings on oxidation resistance of the supports were evaluated by cyclic oxidation testing. Electrical and electrochemical properties of LSCF-SDC cathodes and symmetrical cells deposited on the Y2O3-protected metal supports were also investigated. The issue of Cr depletion of the supports was also discussed.

With increasing attention paid to metal-supported SOFCs recently, metal supports have become important factors in the performance of the cells. The formation of surface oxides and the poisoning of Cr from Cr2O3-forming metal supports often result in the degradation of the cells. However, few studies have focused on developing oxidation resistance and decreasing Cr migration from porous alloys in intermediate temperature metal-supported SOFCs. In this work, Y2O3 and CeO2 coatings were applied to porous AISI 430 stainless steels by sol-gel dip coating. Phases and microstructures of the coatings on the porous metal supports were characterized by XRD and SEM with EDS, respectively. The effects of the coatings on oxidation resistance of the supports were evaluated by cyclic oxidation testing. Electrical and electrochemical properties of LSCF-SDC cathodes and symmetrical cells deposited on the Y2O3-protected metal supports were also investigated. The issue of Cr depletion of the supports was also discussed.

Yttria Partially Stabilized Zirconia (Y-PSZ) plasma-sprayed coatings are widely used in turbine engines as thermal barrier coatings. However, in diesel engines Y-PSZ TBCs have not met with wide success. To reach the desirable temperature of 850-900˚C in the combustion chamber from the current temperature of 400-600˚C, a coating with a thickness of approximately 1mm is required. This introduces different considerations than in the case of turbine blade coatings, which are on the order of 100µm thick. Of the many factors affecting the durability and failure mechanism of TBCs, in service and residual stresses play an especially important role as the thickness of the coating increases. For decreasing the residual stress in the system, a multi-layer coating is helpful. The design of a multilayer coating employing relatively low cost materials with complementary thermal properties is described. Numerical models were used to describe the residual stress after deposition and under operating conditions for a multilayer coating that exhibited the desired temperature gradient. Results showed that the multilayer coating had a lower maximum stress under service conditions than a conventional Y-PSZ coating. Model validation with experiments showed a good match between the two.

Elevated levels of arsenic and other heavy metals like copper, aluminum, zinc, and selenium in drinking water are found to have deleterious effects on human health. Hence, finding methods for reducing their levels is critical. Iron-coated limestone is used as an adsorption material for the removal of heavy metals from drinking water. Removal of heavy metals by native or uncoated limestone was also observed and used for comparison to and evaluation of the improvement in removal efficiency from the ironcoated material. The removal efficiency with limestone was studied for different concentrations of heavy metals. Kinetic studies were done to determine the decrease in heavy metal concentration as a function of time using limestone. Inductively coupled plasma spectroscopy was used for metal analysis. The effective removal rate of copper and aluminum was found to be four hours and one hour, respectively. This method of removal by using limestone is cost effective, eco-friendly, and hence, of great potential importance for heavy metal removal. Iron-coated limestone is used as an adsorption material for the removal of heavy metals from drinking water. This project will investigate techniques to improve removal efficiency of heavy metals using limestone-based material through adsorption. This research will assist in the development of a granular adsorbent product that will remove metals and that can be manufactured and sold for use at the drinking water source, at point-of-use, or at point-of-entry. Limestone is readily available and its use for metals removal is relatively inexpensive. The technology can be adapted to small, rural water supply systems. Benefits of this research will include a low-cost treatment technology for source reduction that will reduce select metals to below drinking water standards.

Graduation date: 1993

This thesis focuses on the tribological performance of tool surfaces in two steel working operations, namely wire drawing and hot rolling. In all forming operations dimensions and surface finish of the products are of utmost importance. Forming basically includes three parts – forming conditions excluded – that may be changed; work material, tool and (possibly) lubricant. In the interface between work material and tool, the conditions are very aggressive with – generally or locally – high temperatures and pressures. The surfaces will be worn in various ways and this will change the conditions in the process. Consequently, the surface finish as well as the dimensions of the formed product may change and in the end, the product will not fulfil the requirements of the customer. Therefore, research and development in regard to wear, and consequently tribology, of the forming tools is of great interest. The investigations of wire drawing dies focus on coating adhesion/cohesion, surface characteristics and material transfer onto the coated steel both in laboratory scale as well as in the wire drawing process. Results show that it in wire drawing is possible to enhance the tribological performance of drawing dies by using a lubricant together with a steel substrate coated by a polished, dual-layer coating containing both hard and friction-lowering layers. The investigations of hot rolling work rolls focus on microstructure and hardness as well as cracking- and surface characteristics in both laboratory scale and in the hot strip mill. Results show that an ideal hot work roll material should be made up of a matrix with high hardness and a large amount of complex, hard carbides evenly distributed in the microstructure. The surface failure mechanisms of work rolls are very complex involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. This knowledge may be used to develop new tools with higher wear resistance giving better performance, lower costs and lower environmental impact.

Papers are coated in order to improve the properties of the surface, to improve printability and to include new functionalities like barriers properties. Typical coating formulation contains a high number of components, some are made from minerals and others are manufactured from petroleum. The barrier properties of today's paper based packages are plastics and/or aluminum             foil. Environmentally friendly substitutie of these nonrenewable materials are needed.  Nanocellulose is a promising material                 and of a growing interest as an alternative to petroleum-based materials, since nanocellulose films/coatings have been shown to have excellent mechanical and barrier properties.   This project aimed to evaluate nanocellulose in combination with minerals in paper coatings. The project had two approaches. One was to evaluate the barrier properties of MFC coatings with mineral included. The second part was about coatings for           printing matters, and evaluation of the possibility to replace petroleum-based binders in the coating color with MFC. Barrier properties were evaluated by measuring the air permeability of the coatings. The properties of the coating affecting the         printability in offset printing examined was the surface energy, the gloss, the roughness of the coatings, the strength and the offset ink setting.   Carboxymethylated nanocellulose formed denser films and had superior barrier properties compared with enzymatically pretreated nanocellulose. Adding of minerals did not affect the barrier properties of the MFC coatings to a significant extent.         Therefore, minerals cannot be added to enhance the barrier but it can be added to reduce the cost of the coating process without losing any barrier properties.                                 The print quality depends on how the ink interacts with the coating. These coatings did have a relatively high surface energy, which is preferable for printing with waterborne ink. It was also shown that the absorption abilities increased when the amount of MFC was increased. However, offset printing demands high surface strength and addition of MFC in the coating color                     drastically decreased the strength. This means that the coatings produced in this work are not strong enough and thereby not           suitable for offset printing. However other printing technologies put lower demand on surface strength and are still possible.