Ni–W diffusion barrier: Its influence on the oxidation behaviour of a β-(Ni,Pt)Al coated fourth generation nickel-base superalloy

A Ni–W base diffusion barrier (DB) has been developed to limit interdiffusion between a fourth generation Ni-base superalloy (MCNG) and a Pt-modified nickel aluminide bondcoat. After long term oxidation, the DB layer permits to reduce the Al depletion in the coating and to delay the phase transformations in the coating. But despite this result, the oxidation behaviour of the system with DB is slightly worse than without the DB. This difference may be caused by the addition of S and/orWin the coating of the system with the DB. The DB layer also delays the Secondary Reaction Zone (SRZ) formation. Nevertheless, the propagation of the SRZ is similar in systems with and without a DB, with growth kinetics which are driven by interdiffusion

Effect of platinum on the growth rate of the oxide scale formed on cast nickel aluminide intermetallic alloys

Thermo-Gravimetric Analysis ( TGA) and Scanning Electron M icroscopy ( SEM ) data of the initial stages of oxidation of Ni50Al50 and Ni40Pt10Al50 alloys of low and high sulfur content at 900◦ C and 1100◦ C are reported. The results show that the addition of Pt promotes the growth of the transient θ- Al2O3 oxide scale. This effect is particularly sensitive in the initial stages of oxidation at 1100◦ C where Pt considerably increases the total mass gain. It is attenuated in the presence of a high sulfur content in the alloy, indicating a competitive effect of Pt and S on the segregation of Al. The slower θ-to- α transition observed in the presence of Pt leads to an extended lifetime of the θ phase layer, which is proposed to be benecial to the relaxation of the stresses created by the growth of α-Al2O3

Development of a NiW in-situ diffusion barrier on a fourth generation nickel-base superalloy

A diffusion barrier based on a NiW electrolytic coating has been developed to limit interdiffusion between a Ni-base superalloy (MCNG) and a β-NiAl bondcoating. Isothermal oxidation tests of 50h at 1100°C confirmed that W-rich layer formed with NiW coating modifies the oxidation behaviour of the bondcoat and limits interdiffusion. The diffusion barrier reduced β-NiAl γ’-Ni3Al transformation in the bondcoating and prevented SRZ formation

Oxidation behaviour of the 47Nb 16Si 25Ti 8Hf 2Al 2Cr alloy sheet and vibrational spectroscopy

International audienc

Oxidation behaviour of the 47Nb 16Si 25Ti 8Hf 2Al 2Cr alloy sheet and vibrational spectroscopy

International audienc

Oxidation behaviour of the 47Nb 16Si 25Ti 8Hf 2Al 2Cr alloy sheet and vibrational spectroscopy

International audienc

Effect of Au diffusion in Au-coated (gamma + alpha2) titanium aluminides

International audienceIn order to understand the role of α2-Ti3Al precipitates during the oxidation of Au-coated γ-48-2-2-TiAl alloys, the γ-TiAl and α2-Ti3Al microstructures resulting from Au diffusion at 900 °C were investigated. The as-obtained coatings were characterized using scanning electron microscopy (SEM), combined energy and wavelength dispersive X-ray spectroscopies (EDS, WDS), electron backscatter diffraction analysis (EBSD), X-ray diffraction (XRD) and isothermal oxidation tests. Results showed that Au-coated-γ-TiAl alloys presented an upper aluminoformer TiAlAu2 layer and a lower non-protective TiAlAu layer, both with narrow homogeneity range, and with thicknesses that could be estimated with the use of the Prasad model. A more complex layer structure is obtained after Au diffusion in α2-Ti3Al alloys, since eight different phases were identified. In the lower layers, two new ternary tetragonal phases (Ti2AlAu and Ti3Al2Au) were found, and a partial diagram for the Al-Au-Ti 900 °C isotherm is proposed. Absence or depletion of Al was found in the upper layers and, in addition, a low oxidation resistance of the Au-coated-α2-Ti3Al alloy was reported

Characterization of a Multiphase Coating Formed by a Vapor Pack Cementation Process to Protect Nb-Base Alloys against Oxidation

International audienc

Characterization of a Multiphase Coating Formed by a Vapor Pack Cementation Process to Protect Nb-Base Alloys against Oxidation

International audienc

Oxidation Behavior of a Spark Plasma Sintered Ti–48Al–2W–0.1B Alloy at 800 °C

International audienceSpark plasma sintering (SPS) enables the manufacturing of TiAl alloys with an exceptional combination of low density and mechanical properties such as acceptable ductility at room temperature and high strength at high temperature. However, TiAl alloys are known to exhibit low oxidation resistance above 700 °C. The oxidation of a Ti–48Al–2W–0.1B (at. %) processed by SPS was investigated at 800 °C. Coupons were oxidized in air and in Ar-21O2 (vol%), in isothermal and cyclic tests. In air, the alloy formed a mixture of Ti and Al oxides, but oxidation was slower than typically observed for W-free alloys. The oxide scale and underlying alloy were characterized by X-ray diffraction and electron microscopy in order to examine the beneficial role of W in the oxidation resistance. The main constituents of the reaction product after reaction in air may be described as follows (from gas to alloy): TiO2/porous Al2O3/TiO2 + Al2O3/TiN + Al2O3 + W/TiAl2 + W/TiAl. Close examination suggests that the relatively good oxidation resistance of the alloy is related to W doping of TiO2 in the mixed Al2O3 + TiO2 layer. The alloy formed an Al-rich oxide scale with much slower kinetics in Ar-21O2, confirming the detrimental role of N in the oxidation process