Master of Science / Department of Mechanical and Nuclear Engineering / Gurpreet Singh / Graphene because of its unique electrical (electron mobility = 2 x 10[superscript]5 cm[superscript]2 V[superscript]-1 s[superscript]-1), mechanical (E = 1 TPa), optical, thermal and chemical properties has generated a lot of interest among the research community in recent years. One of the most notable methods of synthesizing large area pristine graphene sheets, which are several 100 micrometers wide, is through thermal chemical vapor deposition (CVD). But very little has been known about the effects of heating and cooling rate of the substrate on the quality of graphene produced. Hence we varied various growth parameters to understand the process of graphene growth on Cu and Ni substrates when subjected to fast heating and quenching. This allowed optimization of the CVD process to achieve large-area graphene films consistently and repeatedly. This work provides new insights on synthesis of graphene at atmospheric pressures and the effect of (a) fast heating and fast cooling of substrates, (b) catalyst type and (c) gas flow rates on quality of the graphene produced. A carbon nanotube CVD furnace was restored and modified to accommodate graphene synthesis. We started with synthesis of graphene on Cu substrate following procedures already available in the literature (heating rate ~ 15 °C/min and cooling rate ~ 5 °C/min; total processing time 7 hours). This provided a good reference point for the particular furnace and the test setup. The best results were obtained for 15 minutes of growth at a CH4:H2 ratio of 1:30 at 950 °C. SEM images showed full coverage of the substrate by few layer graphene (FLG), which was indicated by the relatively high I[subscript]2D/I[subscript]G ratio of 0.44. The furnace was further modified to facilitate fast cooling (~4 °C/sec) of substrate while still being in inert atmosphere (Argon). The effect of growth time and concentration of CH[subscript]4 was studied for this modified procedure (at H[subscript]2 flow rate of 300 SCCM). SEM images showed full coverage for a CH[subscript]4 flow rate of 10 SCCM in as little as 6 minutes of growth time. This coupled with the fast cooling cycle effectively reduced the overall time of graphene synthesis by 7 times. The I[subscript]2D/I[subscript]G ratio in Raman spectrum was 0.4 indicating that the quality of graphene synthesized was similar to that obtained in conventional CVD. This modification also facilitated introduction of catalyst substrate after the furnace has reached growth temperature (fast heating ~8 °C/sec). Hence, the overall time required for graphene synthesis was reduced to ~6 % (30 minutes) when compared to the traditional procedure. SEM images showed formation of high concentration few layer graphene islands. This was attributed to the impurities on the catalyst surface, which in the traditional procedure would have been etched away during the long heating period. The optimum process parameters were 30 minutes of growth with 20 SCCM of CH[subscript]4 and 300 SCCM of H[subscript]2 at 950 °C. The Raman spectrum for this condition showed a relatively high I[subscript]2D/I[subscript]G ratio of 0.66. We also studied the effect of Ni as a catalyst. Similar to Cu, for Ni also, traditional procedure found in the literature was used to optimize the graphene growth for this particular furnace. Best results were obtained for 10 minutes of growth time with 120 SCCM of CH[subscript]4 in 300 SCCM of H[subscript]2 at 950 °C. SEM images showed large grain growth (~50 μm) with full coverage. The Raman spectrum showed formation of bi-layer graphene with a I[subscript]2D/I[subscript]G ratio of 1.03. Later the effect of growth time and concentration of the hydrocarbon precursor for Ni substrate subjected to fast heating (~ 8 °C/sec) was studied. It was found that because the process of graphene synthesis on Ni is by segregation, growth period or gas flow rate had little effect on the quality and size of the graphene sheets because of the presence of impurities on the substrate. This procedure yielded multilayer graphite instead of graphene under all conditions. Future work will involve study of changing several other parameters like type of hydrocarbon precursor and pressure in the chamber for graphene synthesis. Also various other substrates like Cu or Ni based alloys will be studied to identify the behavior of graphene growth using this novel procedure.

Quenching technique is widely used in industrial applications as it enhances the mechanical properties of metals such as hardness and tensile strength. This technique consists of a heating process followed by fast cooling which results in different microstructures that enhance the metal behavior. Current competitive market in metal field requires the implementation of advanced and optimizing techniques by means of efficient and sustainable quenching techniques. Furthermore, cooling by multiple array of water jets offers wide range of cooling rate control and consequently the achievement of the desired properties. Quenching cooling rate for a rotary cylinder by multiple impinging jets is investigated in this experimental study. A rotating steel cylinder is heated up to 700°C by an induction heater and cooled down in short time by an array of water impinging jets in order to study quenching process of the test specimen by the impinging jet technique. This fast cooling has been found to be a crucial parameter that enhances the characteristics of steel thoroughly. The magnitude of its influence has been previously studied in water pools cooling techniques. Consequently, a further understanding of quenching technique is aimed in this study by the variation of different parameters: the multiple jet’s pattern (inline and staggered), jet-to-jet spacing (S/d=4 and 6), rotational speed (10-70rpm) and water subcooling temperature (55-85K) that have been studied in 10 experiments. Running of the experiments have been done with the help of different programs such as LabVIEW and NiMAX. Measurements of the temperature along the cylinder has been carried out by using some embedded thermocouples that have been connected to the DAQ.  Results from the study revealed faster cooling with rotation speed 30rpm since the contact between hot surface and impinged water jet is improved for lower speeds. However, rotation speed10rpm results experienced negative effects. In addition, jet-to-jet spacing S/d = 4 caused higher cooling rate than S/d = 6 since the impinged water from neighbor jets lead to higher interaction between water fronts and consequently a more uniform cooling. Furthermore, significant differences have been found in temperature drop between points located closer to the center of the cylinder and the ones beneath the cooling surface. Regarding the multiple array configuration of nozzles, staggered configuration revealed more uniform cooling over the surface due to the fact that placement of the jets led to a better distribution of the impinged water in the measurement line. The effect of higher subcooling temperature in agreement with previous studies results in which higher cooling rate and more drastic temperature drop. The aim of this study is to make a better understanding of the multiple water impinging jets quenching technique in order to make further research in the area of enhancing the mechanical properties of steel by understanding effect of the quenching parameters and their characteristics in order to optimize the quenching technique for different applications.

The press hardening belongs to state-of-the-art technology at sheet metal forming to gain high strength and crash resistant parts in automotive industry. This process could establish due to its cost- and esourceefficiency. According to ongoing developments on direct press hardening processes it is necessary to describe and understand the thermo-mechanical treatment of 22MnB5. Therefore the flow behavior and phase transformation during cooling with simultaneous forming is investigated. The experimental process considers industrial parameters in order to get industry-oriented results. In deep drawing processes the sheet metal is roped into the draw die and bended around the die edge. Thereby sheets perform different stages of compressive and tensile strain at the die oriented side and the punch oriented side of the sheet. There are different stages and values of stress and strain according to several layers of the sheet over its cross-section. The values of stress, strain and forming rate were FEcalculated for industry-relevant bending radii and sheet thicknesses of manganese-boron steel 22MnB5. According to the calculations different cooling and forming strategies were performed by dilatometric tests. The forming behavior is described by the microstructural development with regard to the cooling rate and temperature. Beside the influence of austenite forming on the phase transformation and mechanical properties is considered. A prospective view is given to illustrate ongoing examinations under compressive and combined tensional and compressive forces.

The press hardening belongs to state-of-the-art technology at sheet metal forming to gain high strength and crash resistant parts in automotive industry. This process could establish due to its cost- and esourceefficiency. According to ongoing developments on direct press hardening processes it is necessary to describe and understand the thermo-mechanical treatment of 22MnB5. Therefore the flow behavior and phase transformation during cooling with simultaneous forming is investigated. The experimental process considers industrial parameters in order to get industry-oriented results. In deep drawing processes the sheet metal is roped into the draw die and bended around the die edge. Thereby sheets perform different stages of compressive and tensile strain at the die oriented side and the punch oriented side of the sheet. There are different stages and values of stress and strain according to several layers of the sheet over its cross-section. The values of stress, strain and forming rate were FEcalculated for industry-relevant bending radii and sheet thicknesses of manganese-boron steel 22MnB5. According to the calculations different cooling and forming strategies were performed by dilatometric tests. The forming behavior is described by the microstructural development with regard to the cooling rate and temperature. Beside the influence of austenite forming on the phase transformation and mechanical properties is considered. A prospective view is given to illustrate ongoing examinations under compressive and combined tensional and compressive forces.

The diploma thesis is focused on fire-resistant repair mortar with fine-grained filler. The aim of this work is the research and development of fine-grained Mortars resistant to high temperatures, which are characteristic at the beginning of the fire. The theoretical knowledge with subsequently realized laboratory verification was used. At-tention was paid to the masses based on the mixed binder comprising cement and blast furnace slag, respectively. high-temperature ash. Cellulose fibres were used as the dis-persed reinforcement. Two kinds of aggregate were assessed - fly ash agloporit and am-phibolite incl. combinations thereof. Laboratory tests were carried out via determination of basic material properties (density, strength, consistency, dimensional changes etc.) after exposure to extreme temperatures. A substantial part of the research was also study of different cooling conditions - slow and fast (water and air). Selected formulations were subjected to temperatures up to 1200 ° C. In the conclusion is selected several recipes that have been found to be optimal for continuing research on the basis of the results and findings.