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1.
A diffusion-barrier-coating system with a duplex layer structure comprised of an inner Re-base alloy layer and an outer β-NiAl layer was formed on the Ni–Mo alloy, Hastelloy-X. Alloy specimens with and without the coating were oxidized at 970 °C in air for up to 200 h with an imposed tensile stress of 22.5 MPa. The oxidation behavior under the stress-free condition was also investigated for comparison purposes. Strain rates of the specimens with a diffusion-barrier-coating system decreased rapidly for about 5 h, followed by a slow creep-deformation with a strain of 3.5% and strain rates of (0.7–0.2) × 10−7/s for 200 h. There was little change in both the coating structure and the composition (at%) of the inner Re-base alloy layer. Considering the creep behavior of the uncoated alloy, as well as the fact that there were few cracks and flaws in the Re-base alloy layer, it was concluded that this inner layer was subject to creep-deformation along with the alloy substrate. The external scale on the coated alloy consisted mainly of θ-Al2O3 at the early stage of the oxidation/deformation, and with further oxidation the surface scale formed a duplex layer structure consisting of outer plate-like θ-Al2O3 and inner equi-axed Al2O3. There was exfoliation of the outer θ-Al2O3 scale during the creep deformation. After the 200 h oxidation the outer β-NiAl contained (40–50)% Al, while the alloy substrate near the inner layer had less than 1 at% Al. It was found that the Re-base alloy layer acted an effective barrier against inward Al diffusion and outward diffusion of alloying elements.  相似文献   

2.
A diffusion-barrier-coating system having a duplex structure comprised of an inner Re(W)–Cr–Ni layer and an outer Ni-aluminide layer was formed on a fourth generation, single-crystal Ni-base superalloy by using electroplating of Re(Ni) and Ni(W) films, Al- and Cr- (high-Cr and low-Cr) pack cementations, and a combination of the two treatments. With the ReW-high-Cr coating, fine needle- or plate-like precipitates formed in the alloy substrate below the inner Re(W, Cr, Ni) layer, while there was little of this precipitate with the ReW-low-Cr pack-cementation coating. The inner, Re-base alloy layer in the ReW-high-Cr coating was identified to be a σ-(Re,Cr,W,Ni) phase, while the inner layer of the ReW-low-Cr was a mixture of σ-(Re,Cr,W,Ni) and δ-Re(Cr,W,Ni) phases. After heating the coated alloys at 1,150 °C for 100 h in air, the outer Al reservoir layer became β-NiAl containing (31–33)Al with α-Cr particles and fine precipitates of γ′-Ni3Al with both the ReW-high-Cr and ReW-low-Cr treatments. In the case of the ReW-high-Cr coating there were numerous light-colored, needle-like precipitates formed deep in the alloy substrate under the inner layer, while in the case of the ReW-low-Cr coating γ′ appeared near the inner layer. It was found that the inner, Re-base alloy layer acted as a diffusion barrier, and that its structure was maintained with little change in composition after 100 h of oxidation at 1,150 °C. K. Z. Thosin is from Indonesian Institute of Sciences, LIPI.  相似文献   

3.
Matsumura  Y.  Fukumoto  M.  Hayashi  S.  Kasama  A.  Iwanaga  I.  Tanaka  R.  Narita  T. 《Oxidation of Metals》2004,61(1-2):105-124
A β-NiAl coating with or without a Re-base alloy layer was formed on a Nb–5Mo–15W alloy. The coated alloys were oxidized isothermally in air at 1373 and 1473 K. Electroplating of a high (more than 70at.%)-Re–Ni film, Cr-pack cementation, Ni plating, and then Al-pack cementation, in this sequence, formed a coating structure with Re-base alloy and β-NiAl layers. The Re-base alloy layers were comprised of an outer σ-phase in the Re–Cr(Ni) system and an inner χ-phase in the Re–Nb(Cr) system. It was found that reaction between the β-NiAl and the alloy substrate was significantly suppressed when the Re-base alloy layers were present. The Re-base σ and χ phases were found to be good candidates for a diffusion barrier against inward-Al diffusion because they have very low solubilities for Al.  相似文献   

4.
Formation mechanisms of a coating with a duplex layer, outer β-NiAl(Cr) and inner α-Cr(Ni) layer structure on a Ni–40.2 at% Cr alloy were proposed and change in the coating structure was investigated during high temperature oxidation. The Ni–40.2 at% Cr alloy was electro-plated with about 12μm Ni followed by a high Al activity pack cementation at 1073K to form a coated layer with an outer δ-Ni2Al3 and an inner layer containing Al more than 70at% which grew with an inward diffusion of Al. The coated Ni–40.2at% Cr alloy was oxidized at 1373K in air for up to 2592ks. It was found that at the initial stage of oxidation the as-coated layer structure changed to a two-layer, outer β-NiAl(Cr) and inner α-Cr(Ni), structure. Al contents in the α-Cr(Ni) layer was less than 0.3at%. With long term oxidation an intermediate γ-Ni(Cr, Al) layer formed between the outer and inner layers, whereas the inner α-Cr(Ni) layer became thinner and then disappeared after the 2592ks oxidation at 1373K. Coating processes and changes in the coating structure during high temperature oxidation were discussed based on diffusion and composition paths plotted on a Ni–Cr–Al phase diagram  相似文献   

5.
《Intermetallics》2007,15(4):599-606
The oxidation behavior of a Ni3Al-based superalloy IC6 coated with a duplex Re–Cr–Ni–Mo diffusion barrier layer and an Al reservoir layer was investigated in air at 1423 K for up to 1080 ks. The diffusion barrier layer was formed by electroplating Re(Ni) and Ni films on the alloy, followed by Cr pack cementation at 1573 K, and as a result, forms a continuous inner Re–Cr–Ni–Mo diffusion barrier layer and an outer Ni(Cr,Mo,Al) layer. Then a Ni film was electroplated on the Ni(Cr,Mo,Al) layer, followed by Al-pack cementation at 1273 K for 18 ks, to form an Al reservoir layer with a duplex Ni2Al3 and γ-Ni(Cr,Mo,Al) layers. After oxidation at 1423 K in air for 1080 ks, the Al reservoir layer changed to a γ-Ni–4Cr–5Mo–12Al (all in at%) layer, on which a protective α-Al2O3 scale formed. The Re–Cr(Mo)–Ni layer was stable and effectively retarded the interdiffusion between the Al reservoir layer and the alloy, as a result, the depth of the microstructural change zone of the alloy was less than 15 μm. In contrast, the bare and the coated IC6 superalloy only with an Al reservoir layer were significantly oxidized, accompanied by serious spallation of oxide scales. After oxidation at 1423 K for 1080 ks, the depth of the microstructural change zone of the alloy was about 200 μm for the bare and coated alloy only with an Al reservoir layer. These results indicate that the oxidation resistance of IC6 superalloy can be effectively improved by coating with a Re–Cr–Ni–Mo diffusion barrier layer and an Al reservoir layer.  相似文献   

6.
The oxidation behavior of the nickel-base single-crystal superalloy TMS-82+ coated with a duplex Re(W)–Cr–Ni/Ni(Cr)–Al layer was investigated in air at 1,150 °C for up to 100 h. The coating layer was formed by electroplating Re(Ni) and Ni(W) films on the alloy, followed by Cr-pack cementation at 1,300 °C, and as a result, forming a continuous Re(W)–Cr–Ni diffusion-barrier layer. A Ni film containing fine Zr particles was then electroplated on the duplex layer, followed by Al pack cementation at 1,000 °C for 1 and 5 h to form an Al reservoir layer with a duplex Ni2Al3/γ-Ni layer, which changed quickly to γ-Ni phase containing (10∼13)at.% Al for the 1 h Al-pack coat and a mixture of γ′-Ni3Al and β-NiAl phases for the 5 h Al-pack coat during high-temperature oxidation. A protective α-Al2O3 scale formed during oxidation at 1,150 °C in air, and parabolic rate constants of 7.4 × 10−11 and 6.6 × 10−10 kg2 m−4 s−1 were obtained for the 1 h- and 5 h-Al pack-coatings, respectively. There was little change in the structures of the superalloy substrate after oxidation at 1,150 °C in air for up to 100 h. It was found that the Re(W)–Cr–Ni layer remained stable, acting as a diffusion barrier between the alloy substrate and Al reservoir layers.  相似文献   

7.
In this study, aluminized Alloy 617 was prepared by Al-pack cementation of high temperature high Al activity process. The microstructure evolution and microstructural changes of aluminide coating were investigated after Al-pack cementation and high-temperature aging. The aluminide coating was composed of Ni-aluminide layers, such as δ-Ni2Al3, β-NiAl, Cr2Al, Al3 + xMo1 − x, and inter-diffusion zone by pack cementation. After high-temperature aging, the aluminide coating was transformed from the δ-Ni2Al3 to the β-NiAl because of outward Ni diffusion from substrate. The Cr2Al and the Al3 + xMo1 − x were dissolved during aging. On the other hand, the α-(Cr, Mo) particles were precipitated during aging due to the low solubility of alloying elements in the β-NiAl. The β-NiAl newly formed by the outward Ni diffusion during aging and resulted in the formation of the inter-diffusion zone. The inter-diffusion zone consisted of β-NiAl, Ni3(Al, Ti), Cr-rich M23C6 carbide, and sigma phases.  相似文献   

8.
The oxidation of three Ni–xCr–10Al alloys with a constant Al content of 10 at% and containing 3, 5, and 10 at% Cr was investigated at 900–1000°C in 1 atm of pure oxygen and compared to the behavior of Ni–10Al. At both temperatures, an external NiO scale overlying a zone of internal-oxide precipitates formed on Ni–10Al and Ni–3Cr–10Al: in addition, a discontinuous Al2O3 layer formed at the front of the internal oxidation for Ni–3Cr–10Al. An exclusive external scale of Al2O3 formed at most places on Ni–5Cr–10Al at 900°C, while, at some sites, the same alloy formed an outer NiO layer overlying an internal oxidation zone. The scales formed on Ni–5Cr–10Al at 1000°C were complex, but eventually a protective Al2O3 layer developed either at the alloy surface or beneath a region containing a mixture of different oxides. Finally, an exclusive external Al2O3 layer formed on Ni–10Cr–10Al at both temperatures. Thus, the addition of sufficient chromium to Ni–10Al produced a classical third-element effect, inducing the transition between internal and external oxidation of aluminum under a constant Al content. A possible mechanism for the effect of chromium on the oxidation of Ni–10Al is discussed on the basis of an extension to ternary alloys of a criterion first proposed by Wagner for the transition between internal and external oxidation of the most-reactive component in binary alloys.  相似文献   

9.
Yu  Zhiming  Narita  Toshio 《Oxidation of Metals》2001,56(5-6):467-493
The oxidation behavior in air at 1473 K, and sulfidation behavior in a H2S–H2 gas mixture with a sulfur partial pressure of 10–2 Pa at 973 K of Al–Re coated CMSX-4 were studied. Investigation on the sulfidation behavior of the Re-coated CMSX-4 was carried out in a H2S–H2 gas mixture with a sulfur partial pressure of 10–2 Pa at 973 K. The experimental results show that a Re-rich alloy layer was formed between an -Al2O3 layer and the inner concentration zone of Ta and Ti for the CMSX-4 single crystal alloy with an Al–Re coating after oxidation. The Re-rich alloy layer containing Cr, W, Ni, Co, and Mo effectively inhibited the outward diffusion of alloying elements and the inward diffusion of Al. The Al/Re-coated CMSX-4 single crystal alloy had excellent sulfidation resistance; the Re-rich alloy layer, containing W, Ti, Ta, and Mo, which formed during the sulfidation process and located between the alumina scale and the CMSX-4 base alloy, plays a role in inhibiting the outward diffusion of alloying elements. The sulfidation resistance of CMSX-4 single-crystal alloy is greatly improved by a Re coating on the CMSX-4 alloy surface; this is attributed to a Re–Cr–W alloy layer that retarded the outward diffusion of cations and the oxide layer containing Ta, Ti, and Al, which inhibited the inward penetration of sulfur.  相似文献   

10.
A pack cementation process for the co-deposition of Cr, Fe and Al onto open-cell nickel foam was developed. The reticulated open-cell Ni–Cr–Fe–Al foams were annealed to homogenize the material with 18.8 wt.% Cr, 11.3 wt.% Fe and 7.7 wt.% Al. The microstructure and phase composition of the Ni–Cr–Fe–Al foams were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive analysis (EDS). The results show that the coating is uniform and dense along the perimeter of the Ni strut, and consists of three layers: a Cr–Fe outer layer, an inner layer containing mostly Al and a transition zone. After homogenization annealing, the alloyed foams retain the hollow struts structure of the original pure nickel foams and the low relative densities. The Ni–Cr–Fe–Al alloy foams exhibit enhancement in absolute strength as compared to the pure nickel and Ni–35.2Cr foams. Furthermore, the Ni–Cr–Fe–Al alloy foams show excellent oxidation resistance and outperform the chromia-forming Ni–35.2Cr alloy foam after oxidation at 900 and 1000 °C, which is mainly due to its high aluminum and chromium content leading to the formation of a continuous and adherent duplex oxide layer.  相似文献   

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