Cyclic Oxidation of Diffusion Aluminide Coatings

The diffusion aluminide coatings are used for high-temperature applications. Structural materials of particular components degrade during service due to fatigue, creep, oxidation, corrosion and erosion. The requirements of higher efficiency of modern industrial applications increase the development of new structural materials, technologies and protective coatings. Properties of many structural materials such ultimate tensile strength, creep strength and fatigue are generally optimized for maximum high-carrying loading with less emphasis on environmental resistance. For these applications, the performance characteristics are limited by the operating conditions, which can be tolerated by the used materials. The main structural materials for high mechanical and thermal loading are superalloys protected against aggressive environment by coatings. Cyclic oxidation is the superposition of thermal cycles in an oxidation environment. The main goal of the experimental work was to compare the cyclic oxidation of protective Al and AlSi coatings deposited on both Inconel 713 LC and MAR-M247 superalloys. The resulting graph revealed that samples from IN 713 LC without coating show good resistance and their mass change is maintained above zero limit. Samples from MAR 247 LC with both Al and AlSi coatings appear to be the most acceptable selection of combination relating to superalloys/coating

Temperature Dependence of Fracture Characteristics ofVariously Heat-Treated Grades of Ultra-High-Strength Steel:Experimental and Modelling

The temperature dependence of tensile characteristics and fracture toughness of the standardly heat-treated low-alloyed steel OCHN3MFA along with three additionally heat-treated grades was experimentally studied. In the temperature range of 196; 22 °C, all the additional heat treatments transferred the standard steel from a high- to ultra-high strength levels even with improved tensile ductility characteristics. This could be explained by a reduction of the inclusion content, refinement of the martensitic blocks, ductile retained austenite content, and homogenization of the shape ratio of martensitic laths as revealed by metallographic, X-Ray, and EBSD techniques. On the other hand, the values of the fracture toughness of all grades were found to be comparable in the whole temperature range as the cause of a high stress triaxiality in the pre-cracked Charpy V-notch samples. The values of the fracture toughness of the standard steel grade could be predicted well using the fracture model proposed by Pokluda et al. based on the tensile characteristics. Such a prediction failed in the case of additionally heat-treated grades due to the different temperature dependence of the fracture mechanisms occurring in the tensile and fracture-toughness tests. While the tensile samples fractured in a ductile-dimple mode at all temperatures, the fracture-toughness specimens exhibited a transition from the ductile to quasi-brittle fracture mode with decreasing temperature. This transition could be interpreted in terms of a transfer from the model proposed by Rice and Johnson to the model of Tvergaard and Hutchinson

Media and society

This thesis aims to discuss the main political and public aspects in the frame of media development and their changes, which are recalled by media. Political competition and its market behaviour is nowadays very naturally predisposed. Decision-making processes in the political sphere attract the attention not just by the experts, but also by wide and laic community. Behaviour of political leaders is influcnced by several changes approving in the political sphere and its circles. The global approach to media plays the key role, at the hand of political circles, which candidates directly and very hard appeal in all the elector's groups. Also very important factor here is a wide expansion of informative technologies. Racionalization of elective behaviour becomes very often in these days, what in many cases means that voters are still more sceptical to the relationship of the political scenes and its candidates. The more voices belong to that candidates who the voters think about, they refer the most interesting political pre-voting marketing and campaign. These changes shown, lead to the claim, that political parties direct their campaign by the hand of the base of marketing rules. The concept about the consequence of political communication leads to the rising interest of mass media and policy. The..

Media and society

This thesis aims to discuss the main political and public aspects in the frame of media development and their changes, which are recalled by media. Political competition and its market behaviour is nowadays very naturally predisposed. Decision-making processes in the political sphere attract the attention not just by the experts, but also by wide and laic community. Behaviour of political leaders is influcnced by several changes approving in the political sphere and its circles. The global approach to media plays the key role, at the hand of political circles, which candidates directly and very hard appeal in all the elector's groups. Also very important factor here is a wide expansion of informative technologies. Racionalization of elective behaviour becomes very often in these days, what in many cases means that voters are still more sceptical to the relationship of the political scenes and its candidates. The more voices belong to that candidates who the voters think about, they refer the most interesting political pre-voting marketing and campaign. These changes shown, lead to the claim, that political parties direct their campaign by the hand of the base of marketing rules. The concept about the consequence of political communication leads to the rising interest of mass media and policy. The..

Média a společnost

Táto práca si kladie za cieľ prediskutovať hlavné politické a spoločenské aspekty v rámci rozvoja médií a ich zmien, ktoré dané médiá vyvolávajú. Trhové správanie subjektov politickej súťaže je dnes úplne prirodzeným. Rozhodovacie procesy v politickej sfére priťahujú pozornosť nielen odbornej ale i širokej laickej verejnosti. Správanie politických strán je ovplyvnené niekoľkými zmenami prejavujúcich sa vo sfére politiky. Kľúčovú úlohu zohráva globálny prístup k médiám, prostredníctvom ktorých kandidáti aj politické strany priamo a silne apelujú na všetky voličské skupiny. Dôležitým faktorom je aj široká expanzia informačných technológií. Často dochádza k racionalizácií volebného správania, čo v mnohých prípadoch znamená, že voliči sú viac nedôverčivejší vo vzťahu k politickým stranám a ich kandidátom. Najviac hlasov smeruje pre tých kandidátov, o ktorých si voliči myslia, že predkladajú najzaujímavejšiu politickú predvolebnú reklamu a kampaň. Tieto uvedené zmeny vedú k tomu, že politické strany vedú kampane predovšetkým na báze marketingových zásad. Predstava o význame politickej komunikácie vedie ku zvýšenému záujmu práve o vzťah politickej a masovej komunikácie. Vzrastajúce prenikanie médií do politiky vedie k mediokracii, v ktorej sa médiá zmocňujú funkcií politických inštitúcií. Komplexnou a...This thesis aims to discuss the main political and public aspects in the frame of media development and their changes, which are recalled by media. Political competition and its market behaviour is nowadays very naturally predisposed. Decision-making processes in the political sphere attract the attention not just by the experts, but also by wide and laic community. Behaviour of political leaders is influcnced by several changes approving in the political sphere and its circles. The global approach to media plays the key role, at the hand of political circles, which candidates directly and very hard appeal in all the elector's groups. Also very important factor here is a wide expansion of informative technologies. Racionalization of elective behaviour becomes very often in these days, what in many cases means that voters are still more sceptical to the relationship of the political scenes and its candidates. The more voices belong to that candidates who the voters think about, they refer the most interesting political pre-voting marketing and campaign. These changes shown, lead to the claim, that political parties direct their campaign by the hand of the base of marketing rules. The concept about the consequence of political communication leads to the rising interest of mass media and policy. The...Katedra občanské výchovy a filosofieFaculty of EducationPedagogická fakult

Fraktograficznie wspomagana analiza wzrostu pęknięć typu rybie oczy w stali azotowanej

An analysis of the internal fish-eye crack growth in a plasma-nitrided high-strength lowalloy steel specimen has been performed. The study combines information obtained from the fractographical observation of the striations field located near the centre of the fish-eye crack on the specimen subjected to combined bending-torsion loading with the linear elastic fracture mechanics modelling of the fatigue crack propagation. The results suggest that the propagation stage constitutes only a minor part of the total fatigue life, the major part of which is spent on the fatigue crack initiation. This conclusion is consistent with the high cycle and very high cycle fatigue behaviour of specimens without any surface hardening layer.W pracy przedstawiono analizę wzrostu wewnętrznego pęknięcia typu „rybie oko” w plazmowo azotowanej, niskostopowej próbce wykonanej ze stali o wysokiej wytrzymałości. W badaniach powiązano dane otrzymane z obserwacji fraktograficznej pola prążkowanego w pobliżu środka pęknięcia w próbce poddanej złożonemu stanowi obciążenia giętno-skręcającemu z modelowaniem mechanicznym procesu pękania i propagacji szczeliny zmęczeniowej. Otrzymane wyniki wskazują, że faza propagacji stanowi jedynie drobną część całego procesu pękania zmęczeniowego, którego dominującym etapem jest inicjacja pęknięcia. Wniosek ten pozostaje w zgodzie z badaniami nad wysoko- i bardzo wysoko-cyklowym zmęczeniem próbek bez powierzchni utwardzanych

A Fractographic Study of Bending/Torsion Fatigue Failure in Metallic Materials with Protective Surface Layers

Results are given of a fractographic study of biaxial in-phase bending/torsion fatigue fractures in specimens made of nitrided steel and nickel-based superalloy with protective coatings (diffusion coatings and plasma-sprayed thermal barrier coatings). Fracture surfaces were examined by optical and scanning electron microscopes while stereophotogrammetry and optical profilometry were employed to obtain 3D surface data of selected fracture surface regions. The studied materials exhibited a wide range of fracture mechanisms depending on the microstructure and applied mechanical loading