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As a thermal barrier coating (TBC) is exposed to elevated temperatures, oxidation proceeds at the interface between the top coat of the TBC and the bond coat/substrate. This aluminium-rich layer, in the case of the TBC studied in this work, produces an alumina thermally grown oxide (TGO) at the interface. This layer continues to grow as the exposure time increases and is prone to cracking. Failure of the TGO creates a debond which will affect the heat transfer through the system and lead to localised overheating. Samples of an IN6203DS substrate with a CoNiCrAlY bond coat and YSZ top coat have been thermally aged and a selection of these used to determine the morphology of cracking within the TGO. This quantitative information has subsequently been used to determine the effect on the heat transfer performance of the TBC system using a process of inverse modelling.

High-temperature oxidation resistance of gamma titanium aluminides can be achieved by the formation of a continuous scale of slowly growing Al2O3. The formation of such a scale was favored by the addition of small amounts of fluorine. It is shown that fluorine can have a beneficial effect on oxidation resistance in a certain F-range which is quantified by thermodynamic calculations and by experimental investigations. It is assumed that the F-effect offers a significant potential for improvement of the oxidation resistance of technological TiAl alloys.

Electrical conductivity has been measured to monitor the reequilibration kinetics for single crystals of NiO-Cr2O3 solid solutions. It has been found that the rate for the reduction process is higher than that for the oxidation runs, thus indicating that the obtained kinetic data are not purely bulk controlled. The following expressions for the apparent chemical diffusion coefficient have been obtained within the temperature range 900–1200°C and oxygen partial pressure range 1–10−5 atm: % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpu0de9vqpee9Lq% pepeea0xd9q8as0-LqLs-lirpepeea0-as0Fb9pgea0lrP0xe9Fve9% Fve9qapdbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaaieaace% WFebGbaGaadaWgaaWcbaacbiGaa4xmaiaa+bcacaWGYbGaamyzaiaa% dsgaaeqaaOGaeyypa0tefeKCPfgBaGqbciaa9fdacaqFUaGaa0Nmai% aa9jdacaqFxdGaa0xmaiaa9bdadaahaaWcbeqaaiaa91cacaqFYaaa% aOGaa4hiaiaa+vgacaGF4bGaa4hCaiaa+bcadaqadaqaamaalaaaba% Gaa0Nmaiaa9rdacaqFSaGaa0hnaiaa9jdacaqFWaGaa0xSaiaa9fda% caqFYaGaa0xmaiaa9bdacaGFGaGaam4yaiaadggacaWGSbGaai4lai% aad2gacaWGVbGaamiBaiaadwgacqGHflY1cqGHWcaScaWGlbaabaGa% a8Nuaiaa-rfaaaaacaGLOaGaayzkaaaabaGab8hrayaaiaWaa0baaS% qaaiaa+fdacaGFGaGaam4BaiaadIhacaWGPbGaamizaaqaaiaacQca% aaGccqGH9aqpcaqFXaGaa0Nlaiaa9rdacaqF0aGaa031aiaa9fdaca% qFWaWaaWbaaSqabeaacaqFTaGaa0Nmaaaakiaa+bcacaGFLbGaa4hE% aiaa+bhacaGFGaWaaeWaaeaadaWcaaqaaiaa9jdacaqF3aGaa0hlai% aa9ndacaqF0aGaa0hmaGqbaiaa8flacaqF3aGaa0hmaiaa9bdacaGF% GaGaam4yaiaadggacaWGSbGaai4laiaad2gacaWGVbGaamiBaiaadw% gacqGHflY1cqGHWcaScaWGlbaabaGaa8Nuaiaa-rfaaaaacaGLOaGa% ayzkaaaabaGab8hrayaaiaWaaSbaaSqaaiaa+jdacaGFGaGaa4NCai% aa+vgacaGFKbaabeaakiabg2da9iaaikdacaqFUaGaa0Nmaiaa9Lda% caqFxdGaa0xmaiaa9bdadaahaaWcbeqaaiaa91cacaqFYaaaaOGaa4% hiaiaa+vgacaGF4bGaa4hCaiaa+bcadaqadaqaamaalaaabaGaa0Nm% aiaa9vdacaqFSaGaa03maiaa9rdacaqFWaGaaWxSaiaa9jdacaqFYa% Gaa03maiaa9bdacaGFGaGaam4yaiaadggacaWGSbGaamyBaiaad+ga% caWGSbGaamyzaiabgwSixlabgclaWkaadUeaaeaacaWFsbGaa8hvaa% aaaiaawIcacaGLPaaaaeaaceWFebGbaGaadaqhaaWcbaGaa4Nmaiaa% +bcacaWGVbGaamiEaiaadMgacaWGKbaabaGaaiOkaaaakiabg2da9i% aa9bdacaqFUaGaa0xmaiaa9bdacaqF5aGaa4hiaiaa+vgacaGF4bGa% a4hCaiaa+bcadaqadaqaamaalaaabaGaa0Nmaiaa9LdacaqFSaGaa0% Nnaiaa9fdacaqFWaGaaWxSaiaa9ndacaqFYaGaa0hmaiaa9bdacaGF% GaGaam4yaiaadggacaWGSbGaai4laiaad2gacaWGVbGaamiBaiaadw% gacqGHflY1cqGHWcaScaWGlbaabaGaa8Nuaiaa-rfaaaaacaGLOaGa% ayzkaaaabaGab8hrayaaiaWaaSbaaSqaaiaa+ndacaGFGaGaa4NCai% aa+vgacaGFKbaabeaakiabg2da9iaa9ndacaqFUaGaa0xmaiaa9zda% caqFxdGaa0xmaiaa9bdadaahaaWcbeqaaiaa91cacaqFYaaaaOGaa4% hiaiaa+vgacaGF4bGaa4hCaiaa+bcadaqadaqaamaalaaabaGaa0Nm% aiaa9zdacaqFSaGaa0hmaiaa9jdacaqFWaGaaWxSaiaa9jdacaqF0a% Gaa03maiaa9bdacaGFGaGaam4yaiaadggacaWGSbGaai4laiaad2ga% caWGVbGaamiBaiaadwgacqGHflY1cqGHWcaScaWGlbaabaGaa8Nuai% aa-rfaaaaacaGLOaGaayzkaaaabaGab8hrayaaiaWaa0baaSqaaiaa% +ndacaGFGaGaam4BaiaadIhacaWGPbGaamizaaqaaiaacQcaaaGccq% GH9aqpcaqFWaGaa0Nlaiaa9jdacaqFWaGaa0Nmaiaa9bcacaGFLbGa% a4hEaiaa+bhacaGFGaWaaeWaaeaadaWcaaqaaiaa9ndacaqFXaGaa0% hlaiaa9vdacaqFWaGaa0hmaiaa8flacaqFYaGaa0Nnaiaa9rdacaqF% WaGaa0hiaiaadogacaWGHbGaamiBaiaac+cacaWGTbGaam4BaiaadY% gacaWGLbGaeyyXICTaeyiSaaRaam4saaqaaiaa-jfacaWFubaaaaGa% ayjkaiaawMcaaaaaaa!2EB3! $$\begin{gathered} \tilde D_{1 red} = 1.22 \times 10^{ - 2} exp \left( {\frac{{24,420 \pm 1210 cal/mole \cdot ^\circ K}}{{RT}}} \right) \hfill \\ \tilde D_{1 oxid}^* = 1.44 \times 10^{ - 2} exp \left( {\frac{{27,340 \pm 700 cal/mole \cdot ^\circ K}}{{RT}}} \right) \hfill \\ \tilde D_{2 red} = 2.29 \times 10^{ - 2} exp \left( {\frac{{25,340 \pm 2230 calmole \cdot ^\circ K}}{{RT}}} \right) \hfill \\ \tilde D_{2 oxid}^* = 0.109 exp \left( {\frac{{29,610 \pm 3200 cal/mole \cdot ^\circ K}}{{RT}}} \right) \hfill \\ \tilde D_{3 red} = 3.16 \times 10^{ - 2} exp \left( {\frac{{26,020 \pm 2430 cal/mole \cdot ^\circ K}}{{RT}}} \right) \hfill \\ \tilde D_{3 oxid}^* = 0.202 exp \left( {\frac{{31,500 \pm 2640 cal/mole \cdot ^\circ K}}{{RT}}} \right) \hfill \\ \end{gathered} $$ .

The effect of KCl on the corrosion behavior of the austenitic stainless steel 304L was studied at 600 °C in 5% O2 + 40% H2O + N2. The breakdown of the protective oxide was investigated. This was done through a detailed microstructural characterization of the oxide scales formed after 1, 24 and 168 h. The oxidized samples were investigated by SEM/EDX, FIB and STEM/EDX. The presence of KCl(s) causes a breakdown of most of the protective scale, even though it is not in direct contact with KCl(s) particles, starting after just 1 h exposure. A fast growing porous oxide formed in direct contact with (former) KCl(s) particles and an about 2 μm thick scale covered most of the surface. Only some regions were covered by a thin scale. K2CrO4 particles were randomly distributed all over the scale after 1 h exposure. The particles are situated above the oxide scale and are not in direct contact with the subjacent metal. The thin scale contains lower Cr levels than has been observed in corresponding scales formed in the absence of KCl. The breakdown of the protective scale is suggested to be caused primarily by the formation of K2CrO4, depleting the protective oxide in chromium. In addition, chromia evaporation contributes to chromia depletion and breakdown of the protective scale. Very little or no transition metal chlorides were found after breakaway oxidation. Cl is suggested to play a minor role in the initial breakdown of the protective scale. The presence of KCl particles caused local rapid oxidation, which results in an outward growing Fe and Fe–Cr rich porous oxide.

The nitridation behavior of a Ti-5Al and a Ti-5Cr alloy has been examined at 1000°C and compared with the performance of pure titanium, involving gravimetric, metallographic, and microhardness studies. All of the materials corrode in accordance with a parabolic overall weight gain-time regime, pure titanium nitriding faster than either of the alloys. The reduced rates of nitridation of the alloys relative to pure titanium are reflected in the smaller relative depths of nitrogen dissolution in the substrates and may be accounted for by the corresponding decreased diffusivity values for nitrogen. The addition elements appear to play no part in the linear scaling reactions.

The creep and tensile properties of two uranium alloys (U-21 at.% Nb and U-16.6 at. % Nb-5.6 at. % Zr) were determined in the temperature range 750–900°C. The creep data were fitted to an equation of the form $$\dot \varepsilon = k\sigma ^n$$ exp (-Q/RT)which in turn was used to calculate stresses in oxidizing alloy specimens on the basis of elongation measurements made on the specimens during oxidation. The variation of the average stress in the oxide and in the substrate metal is given as a function of time. The details of the mechanism by which stresses are generated during the oxidation of the alloys are discussed. Comparisons of the relative creep and oxidation rates of the alloys with the stress levels observed during oxidation lead to the conclusion that at least for certain specimen geometries the differences in the mechanical properties of the oxide scales and of the parent alloys account in large measure for the differences in the oxidation characteristics of the alloys.

The oxidation behavior in air at 1000–1250°C of four Ni-Cr-W alloys containing sufficient chromium content (∼22 at. % Cr) for protective Cr2O3 formation in a binary Ni-Cr alloy is reported. Generally for alloys high in W (10 and 16 at.% W), the rejection of tungsten into the alloy beneath the scale introduced a steep Cr concentration gradient and slower Cr diffusion such that continuous precipitation of Cr2O3 internal oxides prevented the formation of a Cr2O3 protective scale. The alloy most dilute in W (1.6 at. % W) formed a protective scale at short times with little outer NiO scale, but scale fractures led to internal oxidation and rapid nonprotective kinetics. After an initially rapid oxidation increment to form NiO, the 3 at.% Walloy formed a protective Cr2O3 scale with about the same steady-state parabolic kinetics as a binary Ni-30Cr alloy. The effect of ternary Wadditions on the development of Cr2O3 scales on Ni-Cr-W alloys is considered as a ternary analog to Wagner's description of the oxidation of Cu-Pt or Cu-Pd alloys.