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Graphical abstract Highlights • Oxidation barrier Fe-Cr-silicide coating formed on strategic Nb-18.7Si-Ti/Zr alloys. • Comparative cyclic oxidation testing of uncoated and coated alloys conducted in air. • Coating prevents oxidation, dimensional degradation in air at temp. of 800–1400 °C. • Mechanism of oxidation protection and characteristics of oxide scale are discussed. • The coating is indispensible for critical high-temperature applications of alloys. Abstract The Nbss/Nb 3 Si-Nb 5 Si 3 alloys exhibit good high-temperature strength and creep resistance, and are candidate high-temperature materials for hypersonic aerospace applications. However, their poor oxidation resistance necessitates the application of protective coatings.The present study examines the comparative cyclic oxidation behavior of uncoated and Fe-Cr modified slurry silicide coated Nb-18.7Si, Nb-18.7Si-5Ti and Nb-18.7Si-5Zr (in at.%) alloys in air at temperatures between 800–1400 °C. The uncoated samples showed extensive loose-scale formation from the initial stages of oxidation. On the other hand, the protective multi-phase oxide scale formed on the coating surface prevented dimensional degradation for at least 5–7 h at high temperatures of 1400 °C. [ABSTRACT FROM AUTHOR]

Highlights • Shot peening produced a deformation zone on the top of a TiAl based alloy. • γ/α 2 lamellar structure was collapsed and grains refined in the deformation zone. • Shot peening catalyzed formation of a submicron-thick α-Al 2 O 3 film. • The prior Al 2 O 3 formation prohibited Ti of the alloy from oxidation at 900 °C. Abstract Shot peening, although generally accepted as a useful surface treatment method to improve oxidation resistance of Ni-, Co- and Fe-based alloys, has been less applied to TiAl based alloys. This work shows that a shot peening treatment converts the Ti-45Al-2Nb-2Mn-1B alloy from thermally growing TiO 2 -Al 2 O 3 mixed oxides to an exclusive Al 2 O 3 in air at 900 °C. The basic reason for this is that the shot peening catalyzes formation of an α-Al 2 O 3 thin film, which prevents Ti of the alloy from oxidation at the high temperature. The slow oxidation of the shot-peened alloy mitigates the degradation of typical γ/α2 lamellar microstructure. [ABSTRACT FROM AUTHOR]

A B-modified silicide coating on Nb-Si based alloy was prepared by the method of pack cementation. The oxidation resistance of the B-modified silicide coating was studied in the pest-oxidation temperature range (from 650 °C to 850 °C). Oxidation experiments show that the samples coated with B-modified silicide coating maintain low-rate oxidation and suffer from no pest oxidation at all experimental temperatures. The preferential oxidation of Ti and Si can suppress the formation of Nb 2 O 5 . Besides, the borosilicate scale with high fluidity can seal the cracks and pores in the scale. Thus, the occurrence of pest catastrophe is avoided. [ABSTRACT FROM AUTHOR]

Ti–Al intermetallic alloys have a number of advantages for the manufacture of aviation and car details. The use of these alloys is limited by their oxidation at high temperatures, which is associated with structural features and the presence of micro and nanosized grains. In such materials, grain boundary diffusion of oxygen can be active, which contributes to the acceleration of oxidation upon heating. In this paper, we present a two-dimensional model for research the diffusion which is accompanied by oxidation. The structure of TiAl is specified as symmetrically alternating grains with a clear separation of boundaries and triple junctions between them. Diffusion and chemical properties of grains and boundaries are different. The problem is formulated in a two-dimensional formulation and solved numerically. The influence of changes in the composition over time on the penetration of oxygen is taken into account. For the convenience of numerical research and analysis of the results, dimensionless variables are used. To solve the diffusion equation, an implicit difference scheme of splitting in coordinates is used. The equations of chemical kinetics are solved using an algorithm similar to the implicit Euler method using an iterative procedure. The results demonstrate the influence of different variants of kinetic regimes on the concentration distribution and integral concentrations of reagents and oxides. • A two-dimensional model is used to analysis the oxidation of TiAl alloy. • Grain boundary diffusion and oxidation are modeled for isothermal conditions. • Two kinetic regimes are revealed for the case of oxides accumulation in surface layer and for the case of predominant oxidation along grain boundaries. • It is detected that concentration dependence of diffusion coefficient affects the oxidation dynamics. [ABSTRACT FROM AUTHOR]

The oxidation resistance in air of Ti-48Al-2Cr-2Nb, Ti-48Al-2Nb-0.7Cr-0.3Si, Ti-43.5Al-4Nb-1Mo and Ti-47Al-2Cr-8Nb alloys was investigated in the range of 800–1000 °C. Specimens were machined from the core of bars processed by Electron Beam Melting. Oxidation tests were performed in TGA equipment under isothermal conditions at different temperatures. The composition of the oxide layers was investigated by XRD, SEM-EDS and XPS. Layer exfoliation was observed, starting from different temperatures for the different alloys. When spallation did not happen in a significant extent the oxide layers grew according to a parabolic law. The kinetic rate constants and the activation energies were calculated. These kinetic parameters allowed to assess a rank of oxidation resistance, which can be correlated with the composition of the alloys. [ABSTRACT FROM AUTHOR]

Isothermal oxidation behavior of NbSi 2 coating grown on Nb substrate was investigated in air at 1000–1450 °C. Oxidation rate of NbSi 2 coating increased with temperature at 1000–1300 °C but opposite trend was observed at 1300–1450 °C. Maximum oxidation rate was obtained at 1300 °C due to the highest porosity of oxide scale. Lowest oxidation rate was observed at 1450 °C due to formation of dense oxide scale by combined effect of volatilization of Nb oxide phase, viscous flow and densification of c-SiO 2 . Oxidation resistance of NbSi 2 coating at these temperatures was governed by some inter-related factors. [ABSTRACT FROM AUTHOR]

A Ti 5 Si 3 -containing multiphase MoSiBTiC alloy with a composition of 38Mo–30Ti–17Si–10C–5B (at.%) was designed and produced by arc-melting. The alloy was composed of five phases—Mo solid solution (Mo ss ), Mo 3 Si, Mo 5 SiB 2 (T 2 ), Ti 5 Si 3 and TiC—and consistently has good thermal stability at least up to 1700 °C. The density of the alloy was ∼7.0 g/cm 3 , which is considerably smaller than that of Ni-base superalloys. Microstructure was carefully examined and microstructural anisotropy was confirmed. The anisotropy was considered to be generated by thermal gradient during the solidification process. Microcracking was remarkable across the primary Ti 5 Si 3 phase, which was caused by thermal expansion anisotropy of the Ti 5 Si 3 phase. High-temperature deformability was examined by high-temperature compression tests at 1500 °C. Two kinds of loading axes were chosen for the compression tests with respect to the microstructural anisotropy. The alloy exhibited a peak stress of 450–550 MPa, followed by good deformability at the testing temperature. Microstructure refinement and reduction in microcrack density were observed after hot working. Oxidation tests were conducted on the alloy at 1100 °C and 1300 °C for 24 h. The oxidation curves demonstrated that rapid mass loss finished within several minutes. After that, the mass loss began to slow down and then the specimens' mass decreased almost linearly with increasing testing time. Cross-section observation indicated that oxygen propagated through Mo ss , whereas T 2 and Ti 5 Si 3 phases acted as barriers against oxygen attack during the tests. In addition, it was found that the alloy gained better oxidation resistance after high-temperature deformation, suggesting a positive effect of phase refinement on its high-temperature oxidation resistance. [ABSTRACT FROM AUTHOR]

The influences of alloyed Lu, Hf and Cr on the oxidation and spallation behavior of NiAl were investigated. Although Lu has a “block effect” of Al as Hf does, the oxidation rate of Lu-doped NiAl is significantly higher, due to: (1) inhibitation of θ- to α-Al 2 O 3 transformation in early oxidation stage; (2) stronger scale grain refinement effect and enhanced oxygen transport rate. Segregation of S and C occurs not only at the alloy/scale interface, but also within the scale. Both Lu and Hf can significantly improve the scale adherence. However, This beneficial effect can be easily overcompensated by Cr. [ABSTRACT FROM AUTHOR]

Iridium (Ir) does not form a protective oxide barrier in high-temperature oxidizing environments, leading to a limited lifetime at high temperatures. To improve the oxidation resistance, pure Ir was modified by pack cementation to produce a double-layer iridium-aluminum (Ir-Al) coating. The oxidation behavior investigation on the Ir-Al coatings at temperatures from 1400 °C to 2000 °C demonstrated that the oxidation resistance of the Ir were significantly enhanced after the pack cementation treatment. Further detailed studies showed that the morphology and mass loss of the oxidized Ir-Al coating are considerably affected by the melting and oxidation of the IrAl 2.7(3) . [ABSTRACT FROM AUTHOR]

A MoSiB based coating was applied to the 1st-generation MoSiBTiC alloy using pack cementation process. After conditioning at 1300 °C for 10 h in air, the coating developed into four layers: an oxide layer, a MoSi 2 layer with Mo 5 Si 3 and MoB precipitates, a Mo 5 Si 3 layer, and a MoB+Mo 5 SiB 2 (T 2) layer. However, visible holes often formed in the coating due to defects, and the oxidation proceeded to the substrate during subsequent cyclic oxidation. In a controlled test on a MoSiBTiC alloy with lower TiC volume fraction, an intact coating formed after the conditioning at 1300 °C and provided an effective oxidation resistance. • A MoSiB based coating was applied to the 1st-generation MoSiBTiC alloy. • Visible holes were often formed in the coating after the conditioning at 1300 °C. • An intact coating was formed by reducing the TiC volume fraction in the substrate. • The TiC content plays a critical role in the performance of the silicide coating. [ABSTRACT FROM AUTHOR]

A B-modified silicide coating was prepared on the Nb-Si based alloy by Si-TiB 2 co-deposition at 1300 °C for 10 h. The results show that the two-layer coating is composed of a (Nb, X)Si 2 (X represents Al, Cr, Ti and Hf) + NbTiB 4 outer layer and a (Nb, X)Si 2 + Cr 2 Nb inner layer. Static oxidation tests indicate that the mass gain of B-modified silicide coating was 2.39 mg/cm 2 after oxidation at 1250 °C for 100 h. The good oxidation resistance is attributed to the formation of a continuous and dense scale mainly consisting of glassy borosilicate. [ABSTRACT FROM AUTHOR]

The oxidation resistance of MSi 2 compounds with M = V, Ti, Cr was investigated from 450 to 950 °C in air under isothermal and cyclic conditions. Vanadium, chromium and titanium disilicide were not subjected to the pest phenomenon at 650 °C over 800 1-h cycles. The results demonstrated very low weight gains regardless of the testing conditions. Oxidation tests were also performed over long duration (1000 h) to identify the oxidation products. The MSi 2 compounds were all subjected to the simultaneous oxidation of M and Si despite the formation of a protective silica scale. Increasing the duration of oxidation enhanced the protective properties of the silica scale. Therefore, short-term measurements (by thermogravimetry) did not allow an extrapolation of the MSi 2 lifetime. The formation of molten V 2 O 5 induced a higher oxidation rate of VSi 2 and delayed the establishment of the protective silica scale compared with CrSi 2 and TiSi 2 . [ABSTRACT FROM AUTHOR]

The oxidation behavior in air of three alloys from the Nb–Cr–Mo–Si–B system has been evaluated in the temperature range of 700–1400 °C. The alloy compositions in atomic percent are Nb-25Cr-15Mo-20Si-15B (2015), Nb-25Cr-15Mo-20Si-10B (2010), and Nb-25Cr-15Mo-15Si-15B (1515). Increased oxidation resistance has been obtained for the 2015 alloy at high temperatures. Low temperature pest oxidation is not observed for the 2010 and 2015 alloy and only minimal pest products are obtained in the 1515 alloy. Analysis indicates the oxide scale includes Nb 2 O 5 (monoclinic), CrNbO 4 , and SiO 2 . As-cast microstructural phases include Si-rich C14-NbCr 2 Laves phase, (Nb, Mo) 5 Si 3 silicide and (Nb, Mo) 3 Si silicide. [ABSTRACT FROM AUTHOR]

To understand the role of reactive elements in affecting high-temperature oxidation behavior of two-phase (γ′ + β) Ni–Al alloys, Dy and Hf modified Ni-30Al alloys were designed. The results of oxidation tests conducted at 1100 °C indicated that Dy effectively reduced the oxide scale growth rate and enhanced the scale adhesion, but Hf had no significant effect, especially on scale adhesion, which is very different from that in single phase β-NiAl. Possible mechanisms were discussed by combining the solid solubility of Dy and Hf in NiAl and Ni 3 Al. A principle for selection of reactive element used for single doping was proposed. [ABSTRACT FROM AUTHOR]

The oxidation behaviour of a novel thermal barrier coating (TBC) system on a β-stabilized TiAl alloy was investigated at 900 °C in air containing water vapour and sulphur dioxide. This recently developed system consists of a 7 wt.% yttria partially stabilized zirconia topcoat deposited on fluorine-treated and pre-oxidized TNM-B1 substrate material. During thermal cycling at 900 °C in atmospheres containing either 10 vol.% H 2 O or 0.5 vol.% SO 2 , no spallation of the TBCs was observed for exposure periods exceeding 1000 cycles of 1 h dwell time. Fluorinated samples without TBCs showed similar oxidation behaviour, whereas the untreated TNM-B1 alloy revealed significant oxidation. [ABSTRACT FROM AUTHOR]

The effect of Al content on the spallation behaviour of the thermally-grown oxide (TGO) formed on Ni–Al alloys after oxidation at 1100 °C was investigated. It is found that the spallation of TGO increases with an initial increase of the Al content from 20% to 27.5%, and then decreases with further increase in the Al content up to 55%. It is proposed that the TGO spallation is driven by the effective stress near the TGO/substrate interface and restricted by the yielding strength of the substrate. Both the effective stress and yielding strength are influenced by the Al content. [ABSTRACT FROM AUTHOR]

To protect Cr–50Nb alloys from high-temperature oxidation, the silicide diffusion coating and Si–Al coating were produced by pack cementation. The results indicate that the two coatings have three-layer structure and the interfaces are smooth. Uncoated Cr–50Nb alloy occur catastrophic oxidation at the initial oxidation stage at 1200 °C. However, the scale spalling resistance of the two coatings are improved significantly, and Si–Al coating exhibits excellent resistance to oxidation. During cyclic oxidation in air at 1200 °C for 100 h, the weight loss of Si–Al coating is 1.39 mg/cm 2 and the mass gain is 6.01 mg/cm 2 . [ABSTRACT FROM AUTHOR]

Isothermal oxidation of Al 65 Cr 27 Fe 8 and Al 80 Cr 15 Fe 5 was studied in the 600–1080 °C range. Formation of transient alumina layers is obtained up to 900 °C. On Al 65 Cr 27 Fe 8 transient to α-phase transformations occur when performing oxidation at 1000 °C, together with the possible appearance of (Al 0.9 Cr 0.1 ) 2 O 3 . At 1080 °C, direct formation of α-alumina is obtained. On Al 80 Cr 15 Fe 5 , spallation of the oxide layer during the cooling stage is observed following oxidation at 800 and 900 °C, revealing thermal etching of the underneath alloy surface. At 1050 °C the α -Al 2 O 3 scale is directly formed but plastic deformation and recrystallization of the underneath alloy into several intermetallic phases is observed. [ABSTRACT FROM AUTHOR]

Bulk nanostructured NiAl samples with a grain size of 104 nm have been obtained through cryomilling of NiAl intermetallic feedstock powder and subsequent sintering via SPS. Oxidation testing of these conventional and nanostructured NiAl samples reveals that while the conventional samples have oxidation rates on the order of 10-11 g2/cm4/s across all tested temperatures, nanostructured samples demonstrate decreasing oxidation rates with temperature, as low as 6.78 × 10-13 g2/cm4/s. This decrease in oxidation rate is attributed to an earlier transition through the metastable aluminum oxide phases, resulting in a stable slow growing α-Al2O3 phase earlier in the oxidation tests. In-situ X-ray diffraction (XRD) during high temperature oxidation testing has shown that lattice strain at the surface of the nanostructured samples is substantially higher than conventional, and that the decrease of this lattice strain with temperature is significant. It is believed that the relief of this lattice strain stimulates the earlier θ-α transition seen in the nanostructured samples. [ABSTRACT FROM AUTHOR]

The oxidation behaviour for Nb–Si based alloys was performed in air at 1200 °C and 1250 °C. The weight gains of Nb–24Ti–15Si–13Cr–2Al–2Hf (at.%) alloy and Nb–24Ti–15Si–13Cr–2Al–2Hf–4B–5Ge (at.%) alloy after oxidation at 1250 °C for 100 h were 156.7 mg/cm 2 and 32.5 mg/cm 2 , respectively. The oxide scale of the Nb–24Ti–15Si–13Cr–2Al–2Hf (at.%) alloy was porous and loose, while that of the Nb–24Ti–15Si–13Cr–2Al–2Hf–4B–5Ge (at.%) alloy was dense and protective. The presence of alloyed B and Ge improved the protective SiO 2 phase grown during high temperature oxidation, leading to the formation of a continuous and dense oxide scale. [ABSTRACT FROM AUTHOR]

The microstructure and cyclic oxidation behaviour of β-NiAl alloys doped with two reactive elements (REs) were investigated. Hf and Zr as well as Y and La co-precipitated into one phase during alloy preparation, while Dy and Hf as well as Hf and La precipitated alone into different phases. All the co-doped alloys exhibited reduced oxidation rate as compared to the RE-free alloy. The Hf and Zr, Y and La co-doping even led to lower oxidation rate than the corresponding single-doping. The synergistic effect associated with co-segregation of RE ions on alumina scale growth rate was discussed. [ABSTRACT FROM AUTHOR]

The development of robust high temperature oxidation resistant coatings for Nb-Si based alloy was evaluated for a Mo-Si-B coating system that was applied by a two step process. It is observed that the coating is composed of an outer layer of MoSi2 containing boride dispersoids and an inner layer of unreacted Mo. The mass gain of substrate and Mo-Si-B coating is 190.08 and 1.28 mg cm-2 after oxidation at 1250 °C in dry air for 100 h, respectively. The good oxidation resistance of the coating is attributed to the formation of a continuous borosilicate glass coverage. [ABSTRACT FROM AUTHOR]

Highlights: [•] The coating has the three-layer structure, with a thick (Nb, X)Si2 outer layer. [•] Some “oxide pegs” formed at the interface of the oxide scale and coating. [•] The coating exhibits better cyclic oxidation resistance than the Si–Al coating. [ABSTRACT FROM AUTHOR]

Highlights: [•] NbSi2 is prepared by a cost-effective and less energy extensive process. [•] NbSi2 monoliths do not experience commonly observed deleterious pest oxidation. [•] The oxidation rate of NbSi2 monoliths is decreased dramatically by cyclic oxidation. [•] NbSi2 monoliths exhibited a superior oxidation resistance compared with previous work. [Copyright &y& Elsevier]

Highlights: [•] Oxidation protective layers were deposited on Mo–Si–B alloys by magnetron sputtering. [•] The oxidation behavior was studied at 800, 1000, and 1300°C in air. [•] An aluminum borate scale formed on the Mo–70Al layer. [•] Mo–37Si–24B and Mo–46Si–24B coatings were protective at 800 and 1000°C for up to 100h. [•] The Mo–46Si–24B coating was protective for short times even at 1300°C. [ABSTRACT FROM AUTHOR]

Highlights: [•] Oxidation of reactive elements doped NiAl in humid atmosphere was studied. [•] Dy and La were prone to precipitate and form reactive-element rich oxides. [•] Zr segregated at the scale/alloy interface to form numerous oxide pegs. [•] Water vapor promoted the internal oxidation for Dy and La doped NiAl. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ge modified silicide coating on Nb based in situ composites was prepared. [•] The coating is composed of an outer layer and a transitional layer. [•] The coating has good oxidation resistance due to the formation of GeO2 and SiO2. [ABSTRACT FROM AUTHOR]

Highlights: [•] Oxidation behaviour of Sm, Gd, Yb, Sc and Nd doped NiAl alloys was investigated. [•] The REs reduced the oxidation rate and improved the oxide scale adhesion to NiAl. [•] Yb and Sc greatly inhibited the formation of interfacial voids and scale rumpling. [•] Nb and Ta had no effect on the oxide scale adhesion to NiAl. [Copyright &y& Elsevier]

Highlights: [•] Oxidation behaviour of Cr/Si co-doped NiAlDy alloys is investigated at 1200°C. [•] The effect mechanism of Si and Cr on oxidation of NiAlDy alloys is discussed. [•] NiAlDyCr–3Si reveals low oxidation rate and enhanced oxide scale adhesion. [•] Pair affinity of Si and Cr alleviates deleterious effect of Cr precipitation. [ABSTRACT FROM AUTHOR]

Highlights: [•] High-temperature oxidation of NiAlHf alloys in humid atmospheres was studied. [•] Hf doping improved oxidation resistance of NiAl in dry and humid atmospheres. [•] Water vapour accelerated the formation and growth of voids for undoped NiAl. [•] Pre-oxidation in dry O2 could compromise the effect of water vapour. [ABSTRACT FROM AUTHOR]

Highlights: [•] Silicon aluminide improves thermal-shock resistance of thermal barrier coatings. [•] Aluminide/thermal barrier coating shows good adherence at all interfaces. [•] Silicon improves the bond coat oxidation resistance. [•] Silicon decreases the thermally grown oxide growth rate on the bond coat. [•] Silicon enhances the thermal stability of β-NiAl phase. [ABSTRACT FROM AUTHOR]

Abstract: The internal oxidation zone (IOZ) of a Sm(CobalFe0.22Cu0.08Zr0.02)7.5 alloy formed in air at 700°C was characterized using transmission electron microscopy (TEM). It shows that the internal oxides are varied in composition and size with depth, from mainly fine FeSmO3 in shallow area to larger Sm2O3 in deeper area. The internal oxidation also causes the formation of a thin phase transformation zone between the IOZ and the alloy. The internal oxidation mechanism, together with the oxidation-induced phase transformation of the magnetic matrix phases of the alloy, is fully disclosed. [Copyright &y& Elsevier]

Abstract: Three protective coatings (TiAlCr coating, TiAlN+Al2O3 and TiAlYN/CrN+Al2O3) were deposited on a Ti–45Al–8Nb alloy and exposed at 750°C for oxidation test for 5000h. The materials with Al2O3 top coat showed much better resistance than TiAlCr coating where mainly TiO2 and Al2O3 phases developed. The corrosion kinetics were determined by means of discontinuous gravimetry. The exposed samples were characterised using SEM, EDS and XRD. Artificial neural network was used to predict the kinetic behaviour of the exposed alloys after 2000–4000h of exposure. The predicted kinetic after 5000h shows good agreement with the experimental data. [Copyright &y& Elsevier]

Abstract: The transient stage during isothermal oxidation of Mo76Si14B10 has been studied at 1150°C. The maximum mass loss is found to occur by volatilization of MoO3 within the first 480s of exposure, which is considered to be the transient period. Scanning electron microscopic studies have revealed that a glassy borosilicate layer flows to cover the top surface, and thereby it acts as a protective coating. The thickness of the borosilicate layer increases with exposure time following a parabolic relationship. The mechanism of oxidation during transient period has been discussed with the help of an analytical model. [Copyright &y& Elsevier]

Abstract: Cyclic oxidation of β-NiAl alloys doped with different reactive elements (REs) each of which had an optimized concentration was investigated. All of REs effectively suppressed growth of voids beneath oxide scales formed on the alloys. The La-doped alloy suffered from severe internal oxidation. The Hf or Zr-doped alloys exhibited lower oxidation rate, while the Dy-doped alloy showed less scale rumpling. The effect mechanisms associated with solid solubility and ion size of RE dopants on cyclic oxidation were discussed. Co-doping of REs, such as Dy and Hf or Zr, could be anticipated to provide better cyclic oxidation performance. [Copyright &y& Elsevier]

Abstract: Hot-dip aluminizing and interdiffusion treatment were used to develop TiAl3-rich coatings on a Ti3Al–Nb alloy. The addition of Si, Mn, or Ag to the coatings improves the thickness uniformity and reduces the formation of the through-thickness transverse cracks. The element additions promote the formation of dense and continuous Al2O3-rich scales during the high-temperature oxidation. A layered structure of Al2O3/TiAl3/(TiAl3 +TiAl2)/TiAl/Ti-depleted alloy/alloy from the outside to the inside forms after oxidation at 900°C without changing the main body of the Si- or Mn-modified coating, and the Ag-modified coating develops a layered structure of Al2O3/TiAl3/(TiAl3 +TiAl2)/(TiAl2 +TiAl3)/TiAl/alloy. [Copyright &y& Elsevier]

Abstract: The effect of Al2O3 coating on oxidation was investigated at 900 and 950°C. Isothermal oxidation testing indicated that coating was very effective in reducing the oxidation rate of γ-TiAl. The technology of magnetron sputtering used in this study allowed the deposition of a coating that ensured the improvement of high temperature oxidation resistance. [Copyright &y& Elsevier]

Abstract: The effect of Si on the oxidation resistance of the Nb-20Cr-(10-42)Si alloys has been studied. The major contribution of Si is to produce Nb5Si3 phase which enhances oxidation resistance and the high temperature strength. A range of Si from 10 to 42at.% allows for the determination of microstructural stability especially for the silicides and Laves phases (NbCr2). It has been observed that the weight gain per unit area is lower with increased Si concentration. There may be other silicides besides Nb5Si3 which may be contributing to the oxidation resistance. Characterization has been performed using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) in EDS, BSE and X-ray mapping modes. A comparison between the theoretically expected and experimentally observed micro-constituents has been made. [Copyright &y& Elsevier]

Abstract: The oxidation of a Sm(CobalFe0.22Cu0.08Zr0.02)7.5 magnetic alloy in air at 500, 600 and 700°C has been studied. The temperature increase greatly promotes the external and internal oxidation. The external scale consists of a thin outer layer of CuO and a thicker inner layer of (Co x , Fe1− x )Fe2O4 with distribution of α-Fe2O3. Samarium oxide is not seen in the scale but it is mainly internal oxidation product. Breakaway oxidation is observed at higher temperatures. The mechanisms of external and internal oxidation as well as breakaway oxidation are presented, based on detailed compositional and microstructural characterization of the oxidized zone of the alloy. [Copyright &y& Elsevier]

Abstract: A MoSi2–CrSi2–Si/B-modified SiC coating was prepared by two-step pack cementation. The coating could protect C/C composites from oxidation at 1173K for 600min and at 1873K for 300h and from erosion at 1873K for 50h, respectively. B2O3 oxidised from B-modified SiC layer could seal cracks at intermediate temperatures, resulting in improving the oxidation resistance of the coating. Large cracks caused by the bending of the coated specimens and excessive local stress resulted in the fracture of the tested specimens. [Copyright &y& Elsevier]

Abstract: Aluminizing of bare and 3μm-Pt-electroplated specimens has been utilised to prepare NiAl and low platinum (Ni,Pt)Al coatings. Cyclic oxidation of the coatings was investigated by exposing samples to 1h cyclic oxidation at 1100°C. The modified coating exhibited an external layer of NiAl-25 vol.% PtAl2 above a three-zone structure. This structure endured over the whole testing time, while the NiAl coating failed after 77cycles. The (Ni,Pt)Al coating did not reduce the scale growth rate, but it improved scale adhesion. In addition, Pt limited the outward diffusion of Ti from substrate and hence prohibited formation of undesirable TiO2. [Copyright &y& Elsevier]

Abstract: FeCrNi alloy after aluminizing was oxidized at 1000°C in dry and humid (2.23vol.% water) H2. Experimental results showed that H2 promotes the formation of θ alumina and its transformation to α alumina. The morphology of surface alumina coating does not change significantly, but the oxidation rate of the aluminized layer accelerates by the addition of water vapor. As a result, more cracks are found beneath the alumina layer when water vapor is present. The addition of water vapor seems having a favorable effect on the selective oxidation of Al and concentration of oxygen vacancy in the aluminized alloys. [Copyright &y& Elsevier]

Abstract: High temperature shape memory alloys have received a large interest for many years but none of the systems studied so far has led to industrial applications yet. The titanium-gold system has been reported to develop a martensitic transformation at high temperature but the previous studies did not mention about shape memory effect in a quantitative way. Here are presented first elements concerning the potential of this compound as a high temperature shape memory alloy, from the functional properties and oxidation resistance point of view. A maximum recovered compression strain of 3.9% can be obtained for an initial compression strain of 5% corresponding to a 78% shape recovery, in the range of temperature 850–950 K. A two-way shape memory effect is also reported for the first time for this compound. The oxidation of the alloy at these temperatures seems to be a limitation but its behavior around 700 K is very promising. [Copyright &y& Elsevier]

Abstract: The degradation kinetics of the Ni2Al3/Ni hybrid coating formed on creep resistant ferritic steel is studied by prolonged isothermal annealing experiments at 650°C. The sequence of formation and subsequent consumption of all the intermediate phase layers are determined by intermittent analysis of the specimen at various annealing intervals. It is shown that the Ni5Al3 phase layer starts to form only when the outer Ni2Al3 phase layer is completely consumed and the growth kinetics of each of the intermediate layers differs from that of its subsequent consumption. A model is subsequently formulated to predict the lifetime of the coating studied. [Copyright &y& Elsevier]

Abstract: This particular study includes the analysis of the effect of H2O on promoting the phase transformation in thermally grown aluminum oxides formed on NiAl at 950°C. Oxidation of NiAl is carried out at 950°C in O2 and O2 +15vol.% H2O. It is observed that transient alumina initially formed on NiAl transforms to stable α-alumina in the presence of water vapor which promotes the subject transformation and eventually results in a compact scale, offering superior oxidation resistance. Present study includes the analysis of θ to α-alumina transformation under the effect of temperature and environment. [Copyright &y& Elsevier]

Abstract: The corrosion of thermoelectric clathrates α- and β-Eu8Ga16− x Ge30+ x is studied under static air (DSC/TG) up to 650°C. Oxidation product layers with thicknesses of 10.5μm (α-Eu8Ga16− x Ge30+ x ) and 4.5μm (β-Eu8Ga16− x Ge30+ x ) are formed. The oxidation begins at 360 and 380°C, respectively. XRD pattern of the β-Eu8Ga16− x Ge30+ x oxidized layer shows Ge and four Eu2O3 reflections; while α-Eu8Ga16− x Ge30+ x data (sample crushed and grinded) shows α-Eu8Ga16− x Ge30+ x reflections (majority phase), two EuGa2± x Ge4∓x strongest reflections and Ge (minority phases). These results indicate the amount of oxides is very small or they are amorphous. High temperature powder XRD measurements on α-Eu8Ga16− x Ge30+ x under air confirm the oxidation onset temperature determined in DSC studies. [Copyright &y& Elsevier]

Abstract: To protect carbon/carbon (C/C) composites against oxidation, a Si–Mo coating was prepared on C/SiC-coated C/C composites by a simple slurry method. The microstructure of the coating was characterized by X-ray diffraction, scanning electron microscopy and Raman spectra. Results showed that the coating was mainly composed of SiC, MoSi2 and Si. It could protect C/C composites from oxidation at 1873K in air for 300h and withstand 13 thermal cycles between room temperature and 1873K. The excellent oxidation and thermal shock resistance of the coating was attributed to the formation of dense SiO2 glass at high temperature. The volatilization of MoO3 and SiO2 at 1873K was the main reason of the weight loss of the coated C/C composites. [Copyright &y& Elsevier]

Abstract: Static oxidation in air was performed on Nb–20Cr–20Si–5Al alloy at high temperatures ranging from 700 to 1400°C. Pesting occurred at 700°C while internal oxidation took place at 1300 and 1400°C where Al2O3 initiated at the interface between NbCr2 and Nb9Cr3Si2 phases. Phases present were Nb5Si3, NbCr2, Nb solid solution and Nb9Cr3Si2 depending on the temperature. The aluminium content on each of the phases was analyzed. Al content in Nb9Si2Cr3 has been found to be as high as 5–6 atomic percent. SEM, EDS and XRD techniques were utilized in order to characterize the specimens. [Copyright &y& Elsevier]

Abstract: An ultrafine-grained (UFG) Ni3Al was fabricated by annealing an electrodeposited Ni–Al composite in vacuum at 600°C for 2h. The UFG Ni3Al, compared to a compositional-similar but coarse-grained (CG) alloy prepared by arc-melting, exhibited a greatly increased cyclic oxidation resistance at 900°C. Microstructural investigation showed that the CG alloy grew a scale with a high susceptibility to buckling and cracking because of the formation of large voids at the scale/metal interface, but that the UFG alloy grew an adherent scale, because its typical structure prevented the formation of the interface void during oxidation. [Copyright &y& Elsevier]