The Control of Sulfur Content in Nickel-Base, Single Crystal Superalloys and Its Effects on Cyclic Oxidation Resistance

Sarıoğlu, Cevat; Stinner, Charles P.; Blachere, I. R.; Birks, N.; Pettit, F. S.; Meier, G. H.; Smialek, James L.

doi:10.7449/1996/superalloys_1996_71_80

Cited by 16 publications

(16 citation statements)

References 17 publications

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“…grain boundaries. [31] Grain boundaries also act as preferred Because the crystallographic orientation of cast iron alumisites for void nucleation, [25,31] which likely contributes to nides has shown some effects on scale adhesion, [38] the longaccelerated spallation in these locations. It should also be term scale spallation behavior on NiAl or (Ni, Pt)Al could pointed out that formation of grain boundary voids is not also be affected by coating orientation.…”

Section: Methodsmentioning

confidence: 99%

Synthesis and cyclic oxidation behavior of a (Ni, Pt) Al coating on a desulfurized Ni-base superalloy

Zhang

Lee

Haynes

et al. 1999

Metall Mater Trans A

135

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The influences of sulfur impurities and Pt incorporation on the scale adhesion behavior of aluminide coatings were studied and compared. Low-sulfur NiAl coatings were prepared on a desulfurized, yttrium-free, single-crystal Ni-based superalloy by a modified version of a conventional aluminizing procedure based on chemical vapor deposition. The sulfur level in the resulting NiAl coatings was measured to be less than ϳ0.5 ppmw by glow-discharge mass spectroscopy. Platinum-modified aluminide coatings were synthesized by first electroplating a thin layer of Pt (ϳ7 m) on the superalloy, followed by the same low-sulfur aluminizing procedure. The measured sulfur content in the (Ni, Pt)Al coating was substantially higher than that of the low-sulfur NiAl coating due to contamination during the Pt electroplating process. A very adherent ␣-Al 2 O 3 scale formed on the grain surfaces of the low-sulfur NiAl coating during cyclic oxidation testing at 1150 ЊC, but scale spallation eventually occurred over many of the NiAl grain boundaries. In contrast, despite the higher level of sulfur in the (Ni Pt)Al coating, a very adherent scale was formed over both the coating grain surfaces and grain boundaries during thermal cycling. These results suggest that Pt additions can mitigate the detrimental influence of sulfur on scale adhesion.

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Section: Methodsmentioning

confidence: 99%

Synthesis and cyclic oxidation behavior of a (Ni, Pt) Al coating on a desulfurized Ni-base superalloy

Zhang

Lee

Haynes

et al. 1999

Metall Mater Trans A

135

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“…In the case of nickel based superalloys which show excellent oxidation resistance, cyclic oxidation tests are used commonly in order to evaluate the oxidation resistance of the alloys. 11,12) …”

Section: Oxidation Testsmentioning

confidence: 99%

Degradation of High-temperature Oxidation Resistance for Ni-based Alloys by Re Addition and the Optimization of Re/Al Content.

et al. 2003

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High-temperature oxidation tests were conducted with two groups of Ni-based superalloys in order to elucidate the Re effect on oxidation resistance. One group of alloys was the Ni-8Cr-2Ti-10Al-Re system, characterized by 10 mol% Al content. The other group of alloys was the Ni-8Cr-2Ti-15Al-Re system, characterized by 15 mol% Al content. The alloy compositions were chosen with the aid of the d-electrons concept, so that any undesirable phases would not appear in the microstructure. Both cyclic and isothermal oxidation tests were carried out at 1 373 K for a total time of 720 ks. The oxidation resistance decreased clearly with increasing Re content in the 10-Al series alloys, but did not in the 15-Al series alloys. The alloys having a Re/Al ratio (mol%) up to 0.1 exhibited very small mass change by oxidation, so the Re/Al ratio was indeed a good indication for the design of superalloys having a good oxidation resistance.KEY WORDS: Ni-based superalloy; high-temperature oxidation resistance; Re effect. Alloy PreparationButton ingots of the experimental alloys were prepared by arc-melting under the purified Ar gas atmosphere. Each button ingot was cut into pieces and remelted several times in order to get a compositional homogeneity. The ingots then underwent a solution heat treatment followed by aging heat treatments. The heat treatment conditions were determined on the basis of the experimental data obtained from the differential thermal analysis (DTA). As shown in Table 2, two-steps aging processes were adopted in this experiment. Microstructural ObservationThe heat-treated ingots were cut into small specimens. Those specimens were mounted with a conductive filled phenolic mounting compound and the specimen surfaces were polished with abrasive papers and then with alumina powders down to 0.05 mm mesh. Polished surfaces were etched in the 1 : 1 volume% HNO 3 and HCl solution for about 30 sec. The microstructural observation of the etched specimens of all the alloys was made using a scanning electron microscopy (SEM). The volume fraction of the gЈ phase in each alloy was measured by analyzing the SEM image in a conventional way. Oxidation TestsThe specimens for oxidation tests were prepared by cutting each alloy ingot into 10ϫ5ϫ1 mm size, and then the surfaces were polished mechanically using emery papers down to # 600 grits. Two kinds of oxidation tests were employed in this study. One was the cyclic oxidation test, in which the specimen was kept in a furnace at 1 373 K for 72 ks followed by air cooling in each cycle. This thermal cycle was repeated for 10 times, so the total exposure time at 1 373 K was 720 ks. The other was the isothermal oxidation test, in which the specimen was set in a furnace for the exposure to static air at 1 373 K for 720 ks followed by air cooling. This test temperature is much lower than the solution-heat-treatment temperature and is equal to the firststep-aging temperature (see Table 2), and therefore it is considered that the volume fraction and shape of the gЈ phase scarcely vary.The...

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“…41 Lacking this data, some semi-empirical approaches have attempted to quantify the level of Y required to titrate various sulfur levels in single-crystal superalloys. 35,42,43 Figure 12 displays the final weight change for Rene'N5, having various Y contents and ¾10 ppm S, after oxidation for 1000 one-hour cycles at 1150°C. 43 Adhesion, demonstrated by a low positive mass gain rather than large mass losses, occurred near a Y/S ratio of about ¾1 : 1.…”

mentioning

confidence: 99%

Advances in the oxidation resistance of high‐temperature turbine materials

Smialek

2001

Surface & Interface Analysis

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This overview highlights some of the key factors in understanding the protective ability of aluminum oxide scales for current gas turbine engine alloys and coatings. Dense, phase-pure, slow-growing and adherent scales are required. In most cases, solutions have been found through educated empiricism, with more complete understanding often lagging by decades. Nevertheless, the relentless application of new techniques to answer old questions has often provided radically different viewpoints and pointed the way to new engineering developments. Equally important, this understanding prevents prior misconceptions from taking too strong a hold and maintaining a limited perspective. The microstructure, kinetics, shortcircuit diffusion, phase transformation, growth and residual stresses, interfacial segregation and adhesion provide a richness of topics for this singular and effective system. Copyright INTRODUCTIONThe successful application of many materials requires excellent high-temperature properties. For example, the thermal materials used in electric furnaces, waste incinerators, boilers, heat exchangers and heat engines all require long-term mechanical and chemical stability at high temperatures. The surface stability of the candidate material is necessary to prevent rapid material consumption at high temperatures. In general, this dictates that the exposed material is able to form a slow-growing, stable, adherent surface scale that serves to protect the underlying substrate material. The most important and effective scales are oxides; they are easily produced by reaction with the oxygen in air or in other oxygen-containing H 2 O, CO 2 or CO gaseous environments. And the most sought-after oxide scales are Al 2 O 3 , Cr 2 O 3 , and SiO 2 because of their outstanding protective qualities. Many of the high-temperature components used in aircraft and ground power gas turbines rely on these scales for protection.The purpose of the present review is to highlight some of the recent advances that have been made to high-temperature, oxidation-resistant turbine materials. It is intended to be neither comprehensive nor critical, but rather to give a general, albeit parochial, synopsis of a number of key issues seen to rise to prominence from the perspective of this author. In light of this venue, an attempt will be made to give special emphasis to advances in understanding and performance that were associated with and facilitated by various characterization and surface analysis techniques. Oxidation primerA few points regarding the basic tenents of oxidation theory relevant to all systems are worth reviewing before dealing with specific issues. (The cardinal reference text on the subject, elegantly covering all aspects in great detail, is that by Kofstad. 1 ) Very briefly, the pertinent control issues are the thermodynamics of the possible gas-solid reactions and the diffusion rates of the oxide scales in the presence of a large oxygen activity (P O 2 ) gradient. The free energy of formation of binary oxides ranges from abou...

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The Control of Sulfur Content in Nickel-Base, Single Crystal Superalloys and Its Effects on Cyclic Oxidation Resistance

Cited by 16 publications

References 17 publications

Synthesis and cyclic oxidation behavior of a (Ni, Pt) Al coating on a desulfurized Ni-base superalloy

Synthesis and cyclic oxidation behavior of a (Ni, Pt) Al coating on a desulfurized Ni-base superalloy

Degradation of High-temperature Oxidation Resistance for Ni-based Alloys by Re Addition and the Optimization of Re/Al Content.

Advances in the oxidation resistance of high‐temperature turbine materials

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