Oxidation resistance of ODS alloy PM2000 from 880°C to 1400°C

Oxidation resistance of ODS alloy PM2000 from 880°C to 1400°

Evolution of microstructure and impact-strength energy in thermally and thermomechanically aged 15-5 PH

Due to its outstanding mechanical resistance and resistance to corrosion, alloy 15-5 PH can be beneficially used for manufacturing aerospace structural parts. Following exposure to intermediate temperature, from300◦–400 ◦C, the alloy embrittles through the decomposition of the martensite into iron-rich and chromium-rich domains.Depending on the ageing time, these domains are either interconnected or unconnected with each other. The embrittlement results in a drastic drop of the impact strength-energy and an increase of the ductile-to-brittle transition temperature. The initial microstructure and mechanical properties can be recovered through a re-homogenization of the distribution of chromium and iron atoms in the material in the case where the decomposition of the matrix is not too pronounced. The application of a stress higher than 60 per cent of the yield strength further enhances the ageing kinetics in the case where the combined effect of temperature and time results in the spinodal decomposition of the martensite

Interfacial toughness of the nickel-nickel oxide system

International audienc

Conflicto lingüístico y separatismo en Canadá

Este artículo analiza la historia del conflicto lingüístico entre el pueblo francófono y el pueblo anglófono dentro de la doble realidad cultural de Canadá y muestra el imperialismo inglés hacia el pueblo québécois a lo largo de su historia. Con respecto a la posible independencia de Quebec, el artículo habla a favor de un Canadá unido sin miedo de ofender a los québécois. Y se desprenden dos conclusiones: una emocional y otra racional. La emocional nos recuerda las palabras del profesor Russell: “Amo a Canadá”, “Canadá es un gran país”. En la racional se nos recuerda las trágicas consecuencias de la desintegración de imperios y naciones. Y se afirma que los québécois no van a vivir mejor si se separan del resto de Canadá. Lo que se necesita verdaderamente es un federalismo más interactivo y más económicamente independiente de los Estados Unidos. This article examines the history of the linguistic conflict between Francophones and Anglophones within the double cultural reality of Canada and shows the English imperialism towards the Quebecois throughout their history. With regard to the possible independence of Quebec, the article discusses Canadian unity without fear of offending the Quebecois. Two conclusions stand out: one emotional and another rational. The emotional one reminds us of Professor Russell’s words: “I love Canada”, “Canada is a great place”. The rational conclusion reminds us of the tragic consequences of the disintegration of empires and nations. It is asserted that the Quebecois will not live better if they separate from the rest of Canada. What the country really needs is a federalism, more interactive and more economically independent from the United States

In situ ESEM investigations of the oxide growth on hot work tools steel: effect of the water vapour

5th International Conference on the Microscopy of Oxidation, UNIV LIMERICK, LIMERICK, IRELAND, AUG 26-29, 2002International audienceTempered martensitic steel modified AISI H11 is used in forging processes where tool failure can result from the combination of thermo-mechanical and chemical damage. A better knowledge of the oxidation mechanisms in this material could be useful for a better appreciation of its service behaviour and lifetime. the low chromium content of this Fe-Cr type steel allows the development of mainly Fe2-xCrxO3 oxides with corundum structure and leads to enhanced oxidation in the presence of water vapour. In situ FEG-ESEM images show the scale microstructural modifications during high temperature exposure, as well as the lateral growth of oxide particles. Together with GIXRD, SEM/EDS and SIMS analysis. FEG-ESEM also allows assessment of the H2O effect on oxidation behaviour during high temperature exposures (600 and 700degreesC). Water vapour induces either pores or crystallites size increase, favours faceted oxides particles with enhanced density at the highest partial pressure. At this microscopic scale. anisotropic growth of crystallites is observed, and size expansion rates are found to be linear and characteristic of each individual particle. Temperature acts principally on oxide film microstructure. Whatever the environment, homogeneous scale growth is observed at 600degreesC whereas the steel surface is heterogeneously covered by oxides at 700degreesC

Reinforced sol–gel thermal barrier coatings and their cyclic oxidation life

Cyclic oxidation life enhancement of sol–gel thermal barrier coatings is obtained via the reinforcement of the controlled micro-crack network that forms during the initial sintering of the deposit. Two different sol–gel methods are used to fill in the process-induced cracks, namely dipcoating and spray-coating. Filling parameters, for instance the number of passes or the viscosity of the sol are adjusted, using various techniques such as profilometry and microstructural analysis, to optimise crack filling. Cyclic oxidation tests are implemented at both 1100C and 1150C to investigate the efficiency of the various reinforcement procedures developed and address the influence of the specific microstructure on the oxidation behaviour

Study and prevention of cracking during weld-repair of heat-resistant cast steels

International audienceHeat-resistant cast steels are highly sensitive to cracking as they are weld-repaired because of their very low ductility. To prevent weld-repair cracking of three different heat-resistant cast steels used for the manufacturing of superplastic forming (SPF) dies, the effect of various welding parameters, such as the choice of the filler material, the number of weld passes and the pre-heating temperature has been investigated. The choice of an appropriate filler metal and the pre-heating to 400 °C of the material prior to welding drastically lower the propensity to cracking, but remain unable to eliminate cracks entirely. To further reduce weld-repair cracking and hopefully prevent it completely, a buttering technique has been developed. Buttering of the base metal surface with nickel alloys before weld-repair has been shown to prevent cracking of the base metal, but results in some hot-cracking of the buttering layer itself. On the other hand, buttering with Ni-Fe alloys, less sensitive to hot-cracking, results in crack-free weld repairs

Experimental and numerical investigation of the weld repair of superplastic forming dies

Issu de : AMPT 2003 - International conference on advances in materials and processing technologies, Dublin, IRELAND, July 8-11, 2003International audienceSuperplastic forming process (SPF) is an advanced process conducted at high temperature using moderate strain rates, typically used for shaping TAW sheets for aerospace applications. Thermomechanical stresses on the forming dies due to successive forming cycles may result in the earl), degradation and even fracture of SPF tools through fatigue crack propagation. To reduce cost and extend service life. dies are generally weld-repaired and subsequently re-used in the typical severe conditions of SPF. The implementation of robust, easy processing welding techniques resulting in high quality repair able to sustain cumulative thermomechanical stresses is of utmost concern to SPF parts manufacturers. The paper focuses on the development of an automated TIG technique to weld repair high nickel, high chromium heat resistant alloys based on a complementary approach including thermal instrumentation, numerical simulation using Sysweld(TM) and metallurgical investigation: this former being performed on either as-received, repaired and repaired plus damaged materials

Characterisation of thermal barrier sensor coatings synthesised by sol–gel route

Further improvements in the efficiency of gas turbines are recognised to come from increases in turbine entry temperatures. Accurate temperature measurements are crucial to achieve these increases whilst maintaining reliability and economic component life. The combination of phosphor thermometry and thermal barrier coating (TBC) technology has led to the development of functional temperature sensor coatings which have several advantages over conventional temperature measurement techniques. Developments in sol–gel processing indicate that this method could be used for the production, or particularly, the repair of TBCs in the future. This paper demonstrates, for the first time, that sol–gel processing can be used to make sensor TBCs. The optimum concentration of SmO1.5 was 2 wt.% in YSZ to achieve the brightest phosphorescence emission. Above this concentration the overall intensity of the emission reduces and the transitions from 4F3/2 were suppressed. Furthermore, a similar suppression of these transitions was observed when the product of the sol–gel was heat treated to 1100 ◦C. This was concluded to be due to a higher degree of crystallinity allowing a greater interaction between the dopant ions. The dependence of the phosphorescence spectrum on heat treatment temperature provides the first indication that YSZ produced through sol–gel could be used to detect historic temperatures. An evaluation of the subsurface measurement and temperature capabilities has shown that the phosphorescence can be detected from relatively thin layers, 20 µm, even under 50 µm of undoped YSZ coating. Although the temperature detection range, 400–700 ◦C, is too low for advanced TBCs the material could be used in low temperature regimes or for health monitoring purposes

Influence of isothermal and cyclic oxidation on the apparent interfacial toughness in thermal barrier coating systems

In thermal barrier coatings (TBCs), the toughness relative to the interface lying either between the bond coat (BC) and the Thermal Grown Oxide (TGO) or between the TGO and the yttria stabilized zirconia topcoat (TP) is a critical parameter regarding TBCs durability. In this paper, the influence of aging conditions on the apparent interfacial toughness in Electron Beam-Physical Vapor Deposition (EB-PVD) TBCs is investigated using a specifically dedicated approach based on Interfacial Vickers Indentation (IVI), coupled with Scanning Electron Microscopy (SEM) observations to create interfacial cracks and measure the extent of crack propagation, respectively