With the development of MEMS and nano-technology, effects of tribo-electrification on the size accuracy and quality of micro-element will be more sensitive. The electrification in the order of mV is also important in the nano-machining process. Therefore, the tribo-electrification mechanisms and characteristics between the metal surfaces are investigated in this study. The experiments are conducted on a reciprocating friction tester with a measuring system, and the tribo-electrification behavior is studied for eleven pure metals, namely, Platinum (Pt), Ferrous (Fe), Molybdenum (Mo), Titanium (Ti), Tungsten (W) and Lead (Pb), Zinc (Zn), Aluminum (Al), Silver (Ag), Aurum (Au), Copper (Cu), in dry severe wear process. According to the SEM and EDS observations on the wear particles and the worn surfaces, the tribo-electrification mechanisms between the metal surfaces are proposed. Concerning the study of self-mated pure metal pairs; a model of the tribo-electrification mechanism by asperity removal for five hard metal pairs of Pt/Pt, Fe/Fe, Mo/Mo, Ti/Ti, and W/W is proposed. In this model, the wear for the hard self-mated metals is mainly caused by the asperity removal with small wear particle. When the material transfers from pin specimen to plate specimen, the polarity of tribo-electrification for pin specimen becomes positive, and vice versa. Another model of the tribo-electrification mechanism by junction growth for six soft metal pairs of Pb/Pb, Zn/Zn, Al/Al, Ag/Ag, Au/Au and Cu/Cu is proposed. In this model, the wear mechanism of the soft self-mated metals is the flake-like wear particles that are formed by the particle aggregation with junction growth. The polarity of tribo-electrification for the upper specimen keeps negative due to the wear loss of the upper specimen always less than the plate specimen. Furthermore, the transition mechanisms of tribo-electrification are investigated with changing normal load, hence a map has been established to predict the polarity of tribo-electrification for self-mated metal pairs. That is, with increasing normal load, the polarity of tribo-electrification varies from the random, through tending to negative, to negative, and the formation mechanism of wear particle from the micro-asperity removal, through the transition, to the particle aggregation with junction growth. Moreover, an equation is proposed to predict the average magnitude of tribo-electrification. Results show that the average magnitude of electrification voltage is linearly proportional to the electric resistivity and the relative wear rate, but inversely to the real contact area. Concerning the study of dissimilar metal pairs of Pb/Fe, Ag/Fe, Cu/Fe, Zn/Fe and Al/Fe; the total voltage of tribo-electrification Vt for dissimilar metal pairs consists of three components: (a) tribo-electrification by material transfer Vw, Vw is independent of the reciprocating speed, and is proportional to the (1+n) power of normal load, where n is in the range from ¡V0.5 to ¡V0.9 for lead, silver, copper, zinc, and aluminum. (b) tribo-electrification by friction heat Vf, Vf is linearly proportional to the reciprocating speed, and is proportional to the square root of normal load. (c) tribo-electrification by residual heat Vr, Vr is linearly proportional to the reciprocating speed, and is proportional to the square root of normal load. Moreover, Temperature rise Tt between the contact surfaces can be calculated by Vf and Vr. Hence, Tt consists of two components: (a) temperature rise by friction heat Tf, an equation is proposed to predict Tf. Results show that Tf is a function of friction coefficient, normal load and speed. (b) temperature rise by residual heat Tr, Tr is linearly proportional to the reciprocating speed, and is proportional to the square root of normal load. Finally, a model of tribo-electrification mechanism for dissimilar metal pairs is proposed to describe the tribo-electrification phenomenon for sliding pairs with low to high mutual solubility.

High strength boron steels are commonly used as structural reinforcements or energy absorbing systems in automobile applications due to their favourable strength to weight ratios. The high strength of these steels leads to several problems during forming such as poor formability, increased spring back, and tendency to work-harden. In view of these difficulties, high strength boron steels are usually formed by press hardening at elevated temperatures with a view to facilitate forming and simultaneous hardening by quenching of complex shaped parts.The high strength steel sheets are used with an Al–Si coating with a view e.g. to prevent scaling of components during hot-metal forming. The Al-Si coated high strength steel can lead to problems with galling (i.e. material transfer from the coated sheet to the tool surface) which have a negative influence on the quality of the produced parts as well as the process economy. The available results in the open literature pertaining to high temperature galling are very scarce. With this in view, the friction and wear behaviours of different tool steel coatings and different roughness lay directions sliding against Al–Si-coated high-strength steel at elevated temperatures have been investigated by using a high-temperature reciprocating friction and wear tester at temperature of 900 °C.The results have shown that parallel sliding with respect to the surface roughness lay reduces the severity of galling compared to perpendicular sliding. None of the coatings included in this study have shown beneficial effects in view of galling. The DLC coating experienced less galling compared to the AlCrN and TiAlN. Post polishing of the coated tool steel has resulted in more severe material transfer with higher and more unstable friction. / <p>Validerat; 20111022 (anonymous)</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.

The vision of this thesis is to improve the metal cutting process, with emphasis on the cutting tool, to enable stable and economical industrial production while using expensive tools such as hobs. The aim is to increase the tribological understanding of the mechanisms operating at a cutting edge and of how these can be controlled using different tool parameters. Such understanding will facilitate the development and implementation of future, tribologically designed, cutting tools. Common wear and failure mechanisms in gear hobbing have been identified and focused studies of the material transferred to the tool, in both metal cutting operations and in simplified tribological tests, have been conducted. Interactions between residual stresses in the tool coating and the shape of the cutting edge have also been studied. It was concluded that tool failure is often initiated via small defects in the coated tool system, and it is necessary to eliminate, or minimize, these defects in order to manufacture more reliable and efficient gear cutting tools. Furthermore, the geometry of a cutting edge should be optimized with the residual stress state in the coating, in mind. The interaction between a compressive stress and the geometry of the cutting edge will affect the stress state at the cutting edge and thus affect the practical toughness and the wear resistance of the coating in that area. An intermittent sliding contact test is presented and shown to be of high relevance for studying the interaction between the tool rake face and the chip in milling. It was also demonstrated that material transfer, that can have large effects on the cutting performance, commences already after very short contact times. The nature of the transfer may differ in different areas on the tool. It may include glassy layers, with accumulations of specific elements from the workpiece, and transfer of steel in more or less oxidized form. Both tool coating material, its surface roughness, and the relative speed between the tool surface and the chip, may influence the extent to which the different transfer will occur.

In sheet metal forming (SMF) of materials such as stainless steels there is a major problem with transfer and accumulation of sheet material to the metal forming tool surface. The problem is known as galling; a sort of severe adhesive wear, which results in severe scratching of produced parts. In this thesis, the overall aim was to gain knowledge of the influence of tool steel microstructure on galling initiation under sliding conditions. It was discovered that material transfer and tool steel damage caused by sheet material flow creating wear-induced galling initiation sites occurred in the early stage of galling. The galling resistance was higher for tool steels with higher matrix hardness due to better resistance to tool steel damage. Initial friction and critical contact pressure to galling was influenced by the strength of the sheet material. Material transfer happened at low pressures and the friction value was high in a case of sheet materials with lower proof strength, possibly due to the sheet contact against the tool steel matrix resulting in high adhesion and quicker tool damage. It was demonstrated that, in addition to hardness of the tool steel matrix and sheet material proof strength, tool steel microstructural features like size, shape, distribution and height of hard phases are important parameters influencing galling. Tool steels comprising homogeneously distributed, small and high hard phases better prevented the contact between sheet material and the tool steel matrix. Thus, a metal to metal contact with high friction was more efficiently avoided, which resulted in better tool performance.

The discovery and subsequent synthesis of metal containing fullerenes- IFS (Inorganic Fullerene-like Structures) by R. Tenne et al. has generated considerable scientific interest with great potential impact in many industrial application areas such as lubrication. The lubrication mechanism (tribofilm formation) via exfoliation and deposition of the atomic layers from this cage-like IF-particles was revealed and demonstrated first by this research group. The incorporation of the nanoparticles into lubricants (oils, greases) is however not straightforward. When two surfaces are sliding against each other and a lubricant is used, a thin layer (tribofilm) is formed on the contact area. The friction reducing effects of the nanoparticles can be altered or hindered by certain additives that are used in lubricative oils. The effects of such additives on the tribological behavior of the nanoparticles are investigated by analyzing the tribofilms formed on the worn surfaces using energy-dispersive X-ray spectroscopy in a scanning electron microscope. Another challenge of nanoparticles in lubricants is the penetration of the nanoparticles into the contact zone. A possible solution of this problem is briefly discussed. A modified burnishing technique can be used to coat sliding metallic surfaces with a friction reducing tribofilm. The morphology and composition of these tribofilms was investigated with analytical electron microscopy techniques. In the second part of the thesis electron microscopy was used to investigate the material transfer. Titanium is an elements with high adhesive ability to the counter surface, it displays poor tribological properties in sliding metallic contacts. This can lead to material transfer and consequently severe surface damage. The cold formation and machining of titanium, thus can lead rapid tool wear and poor surface finish. Electron microscopy techniques were used to study the mechanism of titanium transfer to different counter surfaces.

In sheet metal forming (SMF) of materials such as stainless steels there is a major problem with transfer and accumulation of sheet material to the metal forming tool surface. The problem is known as galling; a sort of severe adhesive wear, which results in severe scratching of produced parts. In this thesis, the overall aim was to gain knowledge of the influence of tool steel microstructure on galling initiation under sliding conditions. It was discovered that material transfer and tool steel damage caused by sheet material flow creating wear-induced galling initiation sites occurred in the early stage of galling. The galling resistance was higher for tool steels with higher matrix hardness due to better resistance to tool steel damage. Initial friction and critical contact pressure to galling was influenced by the strength of the sheet material. Material transfer happened at low pressures and the friction value was high in a case of sheet materials with lower proof strength, possibly due to the sheet contact against the tool steel matrix resulting in high adhesion and quicker tool damage. It was demonstrated that, in addition to hardness of the tool steel matrix and sheet material proof strength, tool steel microstructural features like size, shape, distribution and height of hard phases are important parameters influencing galling. Tool steels comprising homogeneously distributed, small and high hard phases better prevented the contact between sheet material and the tool steel matrix. Thus, a metal to metal contact with high friction was more efficiently avoided, which resulted in better tool performance.

Since the 20th century, the distribution of European heathlands rapidly decreased due to agricultural intensification, heavy use of artificial fertilizers or acidification. Therefore, various attempts of heathland restoration are under way in these days. Analysis of nematode community composition can be one of the tools suitable for succession evaluation. In 2011, 2013 and 2014, soil samples were collected from heathland restoration experiment (launched in 2011) where different restoration methods were applied in a 3 × 3 factorial experiment; existing heathlands were also sampled to identify the target community both in dry and wet heathland. A total of 60 samples of extracted nematodes were analysed for absolute abundance, trophic groups, and genera dominance. Various indices were calculated to describe the nematode community. We were able to proove faster development of wet heathlands towards the target community. However, because of large data variability, there was no significant difference between treatments. Development of wet and dry heathlands differed also in increased proportion of omniphagous nematodes in 2013 and predators in 2014 in dry heathlands. After three years of heathland restoration, nematode community has not yet reached parameters of the target community. Key words: Nematoda,...

Additive manufacturing (AM) is a quickly rising method of manufacturing due to its ability to increase design freedom. This allows the manufacturing of components not possible by traditional subtractive manufacturing. AM can greatly reduce lead time and material waste, therefore decreasing the cost and environmental impact. The adoption of AM in the aerospace industry requires strict control and predictability of the material deposition to ensure safe flights.  The method of AM for this thesis is Laser Metal Deposition with wire (LMD-w). Using wire as a feedstock introduces a potential problem, the material transfer from the wire to the substrate. This requires all process parameters to be in balance to produce a stable deposition. The first sign of unbalanced process parameters are the material transfer stabilities; stubbing and dripping. Stubbing occurs when the energy to melt the wire is too low and the wire melts slower than required. Dripping occurs when too much energy is applied and the wire melts earlier than required.  These two reduce the predictability and stability that is required for robust manufacturing.  Therefore, the use of thermal simulations to predict the material transfer stability for LMD-w using Waspaloy as the deposition material has been studied.  It has been shown that it is possible to predict the material transfer stability using thermal simulations and criterions based on preexisting experimental data. The criterion for stubbing checks if the completed simulation result produces a wire that ends below the melt pool. For dripping two criterions shows good results, the dilution ratio is a good predictor if the tool elevation remains constant. If there is a change in tool elevation the dimensionless slenderness number is a better predictor.  Using these predictive criterions it is possible to qualitatively map the process window and better understand the influence of tool elevation and the cross-section of the deposited material. / Additiv tillverkning (AT) är en kraftigt växande tillverkningsmetod på grund av sin flexibilitet kring design och möjligheten att skapa komponenter som inte är tillverkningsbara med traditionell avverkande bearbetning.  AT kan kraftigt minska tid- och materialåtgång och på så sett minskas kostnader och miljöpåverkan. Införandet av AT i flyg- och rymdindustrin kräver strikt kontroll och förutsägbarhet av processen för att försäkra sig om säkra flygningar.  Lasermetalldeponering av tråd är den AT metod som hanteras i denna uppsats. Användandet av tråd som tillsatsmaterial skapar ett potentiellt problem, materialöverföringen från tråden till substratet. Detta kräver att alla processparametrar är i balans för att få en jämn materialöverföring. Är processen inte balanserad syns detta genom materialöverföringsstabiliteterna stubbning och droppning. Stubbning uppkommer då energin som tillförs på tråden är för låg och droppning uppkommer då energin som tillförs är för hög jämfört med vad som krävs för en stabil process. Dessa två fenomen minskar möjligheterna för en kontrollerbar och stabil tillverkning.  På grund av detta har användandet utav termiska simuleringar för att prediktera materialöverföringsstabiliteten för lasermetalldeponering av tråd med Waspaloy som deponeringsmaterial undersökts. Det har visat sig vara möjligt att prediktera materialöverföringsstabiliteten med användning av termiska simuleringar och kriterier baserat på tidigare experimentell data. Kriteriet för stubbning kontrolleras om en slutförd simulering resulterar i en tråd som når under smältan.  För droppning finns två fungerande kriterier, förhållandet mellan svetshöjd och penetrationsdjup om verktygshöjden är konstant, sker förändringar i verktygshöjden är det dimensionslös ”slenderness” talet ett bättre kriterium.  Genom att använda dessa kriterier är det möjligt att kvalitativt kartlägga processfönstret och skapa en bättre förståelse för förhållandet mellan verktygshöjden och den deponerade tvärsnittsarean.

The work deals with the examination of repression and segregation in asphalt mixtures. The theoretical part is monitoring the current situation about the problem of segregation, which mainly refers to the practical adjustments during laying „risking“ asphalt mixtures on the formation of segregated places in the shelter layers of roads. The practical parts of the thesis are summarised measurements on six samples of the most commonly used asphalt mixtures to determine the segregation depending on the selected parameters. The work is describing and valorising a test for determining segregation according to ČSN EN 12697-15.