Influence of the microstructural homogeneity on the high-temperature oxidation behavior of a single crystalline Ni-base superalloy

Pistor, Julian; Hagen, S. P.; Virtanen, Sannakaisa; Körner, Carolin

doi:10.1016/j.scriptamat.2021.114301

Cited by 21 publications

(9 citation statements)

References 41 publications

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“…These additively manufactured single crystals show an unprecedented level of homogeneity which cannot be reached with conventional methods and which leads to superior properties such as the high temperature strength 17 , oxidation resistance 18 , creep strength 17 or fatigue life 16 .…”

Section: Introductionmentioning

confidence: 99%

A novel mechanism to generate metallic single crystals

Pistor

Körner

2021

Sci Rep

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Generally, the evolution of metallic single crystals is based on crystal growth. The single crystal is either produced by growing a seed single crystal or by sophisticated grain selection processes followed by crystal growth. Here, we describe for the first time a fully new mechanism to generate single crystals based on thermo-mechanically induced texture formation during additive manufacturing. The single crystal develops due to two different mechanisms. The first step is a standard grain selection process due to directional solidification, leading to a pronounced fiber texture. The second and new mechanism bases on successive thermo-mechanically induced plastic deformations and texture formation in FCC crystals under compression. During this second step, the columnar grain structure transforms into a single crystal by rotation of individual grains. Thus, the single crystal forms step by step by merging the originally columnar grain structure. This novel, stress induced mechanism opens up completely new perspectives to fabricate single crystalline components and to accurately adjust the orientation according to the load.

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Section: Introductionmentioning

confidence: 99%

A novel mechanism to generate metallic single crystals

Pistor

Körner

2021

Sci Rep

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“…[17] A suitable example for appropriate oxidation resistance is the widely used commercial second-generation Ni-base alloy CMSX-4 that develops a dense alumina layer at the scale/alloy interface during exposure at 1050 °C in air. [18][19][20] In contrast, no protective alumina layer was found in Co/Ni-base model alloys with significantly higher levels of Co compared to Ni after exposure above 800 °C. [12,21] However, some alloy compositions indicated the formation of a Cr-containing spinel layer that was demonstrated to slow down oxidation at 900 °C.…”

Section: Introductionmentioning

confidence: 93%

“…The decision to 850 °C as the lower exposure temperature was made to provide comparability to former studies. [9,10,12,20] As the development of superalloys targets on increasing the maximum service temperature, for the application-oriented superalloys ERBOCo-1 and ERBO-Co-1X experiments well beyond 850 °C were of particular interest, too. Since the c¢-volume fraction significantly lowers beyond this temperature [1] and again in order to provide comparability to available literature, [1,19,20] 1050 °C were chosen to address the high-temperature regime.…”

Section: B Oxidationmentioning

confidence: 99%

“…It is noteworthy that the short heat treatment (HTS) was insufficient to gain equal elemental distributions, as still a considerable degree of segregation as well as some precipitates of a phase other than c and c¢ are detectable (Figure 2). Within the dendritic regions Co and Cr, but especially W are still on above-average concentrations, not only in the case of both ERBOCo alloys, but also in the case of CMSX-4 (see Reference [20]).…”

Section: A Influence Of Homogenization Annealing On Microstructure An...mentioning

confidence: 99%

“…Similar to the ERBOCo system, the dendritic regions of CMSX-4 are especially prone to oxidation. [20] Fig. 16 Therefore, formation of compact alumina scales can be excluded (Figure 16(a)).…”

Section: Oxidation Resistance With Respect To Cmsx-4mentioning

confidence: 99%

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Influence of the Co/Ni Ratio and Dendritic Segregations on the High-Temperature Oxidation Resistance of Multinary Co-Rich Superalloys at 850 °C and 1050 °C

Hagen

Weiser

Abu-Khousa

et al. 2022

Metall Mater Trans A

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Excellent inherent oxidation resistance is a prerequisite for the use of superalloys in many high-temperature applications. To achieve this goal, typically continuous alumina and chromia scale growths are assured through sufficient Cr and Al additions. Since the intended γ/γ′-microstructure of superalloys is only stable within a certain compositional window, the maximum concentrations of these protective scale forming elements are, however, dependent on the overall alloy composition. The latter is a severe drawback, especially for Co-rich superalloys, as for these the maximum content often is insufficient for reaching the desired continuous scale growth. In recent years, the addition of significant Ni levels was identified to improve the high-temperature oxidation properties in the case of simple model alloy systems. In this study, we compare the high-temperature oxidation behavior of two complex Co-rich multinary single-crystalline γ/γ′-strengthened superalloys that only differ regarding their Co/Ni ratios to the commercial Ni-base superalloy CMSX-4. Therefore, time-resolved isothermal gravimetric analysis (TGA) in synthetic air at 850 °C and 1050 °C for 100 hours, scanning electron microscopy analysis (SEM), and electron probe microanalysis (EPMA) were conducted. The results point out that a high Co-content beneficially affects the oxidation resistance at 850 °C, meaning that the Ni-base CMSX-4 is slightly outmatched by the Co-rich competitors. In contrast, at 1050 °C, the commercial (most Ni-rich) alloy performed best and, clearly, an increasing Co-content was identified to deteriorate the oxidation resistance. This temperature-dependent influence of the nominal Co/Ni ratio on oxidation resistance is shown to be especially pronounced for dendritic regions. Consequently, the latter could be identified to especially determine the overall oxidation kinetics.

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