Thesis Theme is the reconstruction of the cultural house in Suchý Důl. The building is divided into a restaurant with rooms and multi-purpose hall with facilities. Reconstruction of the building is additional insulation of substructures, exchange floor structures, replacing ceiling structures, creating new roof construction, replacement of doors, windows and changing the layout. The reconstruction and extension of the part of the building.

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<p>With the poor room temperature formability of magnesium, rare earth (RE) additions have proven a promising avenue for wrought magnesium products. However, not much is known regarding the effect of these elements on strength and ductility. Stanford et al. (2010b) summarized it best: “Although the addition of rare earth elements offers the possibility of greatly improved mechanical properties, we still lack fairly basic knowledge about the behaviour of these alloying elements”[p.6773]. Through a systematic study across three Mg-RE binary systems, the effect of gadolinium, samarium and scandium on solution strengthening, work hardening behaviour and strain rate sensitivity of Mg-RE binary alloys have been characterized.</p> <p>The results suggest that samarium offers the greatest solid solution strengthening in both tension and compression relative to the other two binary systems. For the binary alloys explored, only gadolinium and samarium in compression followed the Labusch theory of solution strengthening; in which the yield strength scales with c^2/3 . Gadolinium additions provide the largest strength and ductility in tension and compression. Increasing solute content in the binary systems leads to a decrease of the strain rate sensitivity of the alloys. At the highest level of solute, both Mg-Gd and Mg-Sm exhibit negative strain rate sensitivity under tension. In compression, Mg-Gd also exhibits a negative strain rate sensitivity at the highest level solute, whereas Mg-Sm has a low, but positive value. The asymmetry in work hardening behaviour and the form of the flow curves between tension and compression is the result of the difference in the dominating modes of deformation at a given stage of the plastic flow. The extent of the work performed established the hardening levels and thermodynamic deformation parameters which control the flow stress and work hardening behaviour, that can be applied in future work.</p> / Master of Applied Science (MASc)

In comparison to traditionally fabricated steels that can undergo extensive processing to produce a complex-shaped component, the powder metallurgy (PM) technique can provide a more efficient approach as it is capable of producing intricately-shaped components that require little to no additional processing and machining [1], [2]. A key factor in being able to do so pertains to quenching and utilizing an appropriate quenching agent that can provide dimensional stability to the part being quenched [3], [4]. To ensure that a PM component can perform equally well when being quenched by a quenchant of reduced cooling capability, the PM component should be if not more, then just as hardenable. Steel hardenability can inevitably be improved with the increase of overall alloying content [5], however, if overall alloying content is to be kept at a minimum, the concept of lean PM steel design is one worth investigating; where a lean steel entails that each and every alloying addition is utilized to its maximum potential. This study evaluates the homogenization behaviour of alloying elements in PM steels during sintering as well as the efficiency of wide-spread industrial practices involving the use of various master alloys and ferroalloys, and investigates the realm of liquid phase sintering to understand and optimize the homogenization behaviour of alloying elements and mechanical properties of PM steels. In the context of this work, multi-component master alloys contain at least three of non-ferrous metals as alloying elements and ferroalloys are master alloys containing iron in addition to typically a maximum of two other non-ferrous alloying additions. Part one of this study discusses a combination of thermodynamic software (DICTRA and Thermo-Calc), incremental sintering experiments and scanning electron microscopy (SEM) - wavelength dispersive spectroscopy (WDS) that were used in order to form a deeper understanding of the homogenization behaviour of alloying elements within PM steel during sintering. Electron microscopy analyses on partially and industrially sintered components provide elemental maps to track the evolution of alloying elements as they relax to homogeneity. Electron microscopy analyses for this portion of the study were conducted on an industryproduced automotive component that was sectioned and sintered industrially as well as experimentally at 1280°C for 30 minutes and 13.4 hours. DICTRA simulations carried out for this research provide a 1-D insight into the evolution of concentration profiles and phases throughout various sintering times for systems involving Cr, Mn, C and Fe. DICTRA simulation results of alloying sources were studied alongside alloying element profiles obtained by compiling point quantification from wavelength dispersive spectroscopy maps for the sintered automotive component. Computational results provided conservative, semi-quantitative recommendations on optimal alloy addition forms that lead to an improvement in homogenization. Part two of this study involves the approach of fabricating and testing multi-component master alloy additions. As these materials are widely employed in PM and are typically fabricated by solidification, their states are non-equilibrium and therefore have regions containing phases precipitating in the beginning of freezing which have higher melting temperatures than regions with phases forming later on. During heating, it is hypothesized that Scheil’s solidification path backtracks and as a result, a fraction of liquid in the ferroalloy can be estimated at sintering temperature. If the fraction is significant, the utilization of this ferroalloy implies liquid phase sintering. Through a combination of Thermo-Calc and Fortran softwares, multi-component ferroalloys with promising compositions were discovered in Fe-C-Cr-Mn, Fe-C-Cr-Mn-Ni, FeC-Mn-Mo, Fe-C-Mn-Mo-Ni and Fe-C-Cr-Mn-Mo-Ni systems for low temperature liquid phase sintering. Those of the Fe-C-Cr-Mn-Mo, Fe-C-Cr-Mn-Mo-Ni and Fe-Mn-Mo-Ni system were fabricated and tried in practice. Compositional maps and mechanical properties of PM steels made with variations of this specially tailored multi-component master alloys were compared with those for which traditional alloy additions were used. / Thesis / Master of Applied Science (MASc)

For ecological reasons, the current main challenge of the automotive industry is to reduce the fuel consumption of vehicles and then emissions of greenhouse gas. In this context, steelmakers and automotive manufacturers decided for some years now to join their efforts to promote the development and use of advanced high strength steels such as TRIP steels. A combination of high strength and large elongation is obtained thanks to the TRansformation Induced Plasticity (TRIP) effect. However, improvement of the mechanical properties is still possible, especially by the refinement of the matrix. In this work, two main ways were followed in order to reach improved properties. The classical way consisting of the annealing of cold-rolled samples and an innovative way consisting of obtaining the desired microstructure by direct hot rolling of the samples. In the classical way, this refinement can be obtained by acting on the chemical composition (with such alloying elements like Cu and Nb). It was observed that complete recrystallisation of the ferrite matrix is quite impossible in presence of Cu precipitates. In addition, if the ferrite recrystallisation is not completed before reaching the eutectoid temperature, the recrystallisation will be slowed down by a large way. An innovative heat treatment consisting in keeping the copper in solid solution in the high-Cu steel was developed. Therefore, ferrite recrystallises quite easily and very fine ferrite grains (~1µm) were obtained. In the innovative way, the effects of hot-rolling conditions on TRIP-assisted multiphase steels are of major importance for industrial practice and could open new dimensions for the TRIP steels (i.e. thanks to precipitation mechanisms leading to additive strengthening). Impressive mechanical properties (true stress at maximum load of 1500 MPa and true strain at uniform elongation of 0.22) were obtained with a relatively easy thermomechanical process, the role played by Nb being essential.

No description available.

No description available.

For ecological reasons, the current main challenge of the automotive industry is to reduce the fuel consumption of vehicles and then emissions of greenhouse gas. In this context, steelmakers and automotive manufacturers decided for some years now to join their efforts to promote the development and use of advanced high strength steels such as TRIP steels. A combination of high strength and large elongation is obtained thanks to the TRansformation Induced Plasticity (TRIP) effect. However, improvement of the mechanical properties is still possible, especially by the refinement of the matrix. In this work, two main ways were followed in order to reach improved properties. The classical way consisting of the annealing of cold-rolled samples and an innovative way consisting of obtaining the desired microstructure by direct hot rolling of the samples. In the classical way, this refinement can be obtained by acting on the chemical composition (with such alloying elements like Cu and Nb). It was observed that complete recrystallisation of the ferrite matrix is quite impossible in presence of Cu precipitates. In addition, if the ferrite recrystallisation is not completed before reaching the eutectoid temperature, the recrystallisation will be slowed down by a large way. An innovative heat treatment consisting in keeping the copper in solid solution in the high-Cu steel was developed. Therefore, ferrite recrystallises quite easily and very fine ferrite grains (~1µm) were obtained. In the innovative way, the effects of hot-rolling conditions on TRIP-assisted multiphase steels are of major importance for industrial practice and could open new dimensions for the TRIP steels (i.e. thanks to precipitation mechanisms leading to additive strengthening). Impressive mechanical properties (true stress at maximum load of 1500 MPa and true strain at uniform elongation of 0.22) were obtained with a relatively easy thermomechanical process, the role played by Nb being essential.

published_or_final_version / Public Administration / Master / Master of Public Administration

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