Effect of Cr addition on γ–γ′ cobalt-based Co–Mo–Al–Ta class of superalloys: a combined experimental and computational study

Baler, Nithin; Samanta, Atanu; Makineni, Surendra Kumar; Alam, Talukder; Pandey, Prafull; Singh, Abhishek K.; Banerjee, Rajarshi; Chattopadhyay, K.

doi:10.1007/s10853-017-1159-6

Cited by 63 publications

(9 citation statements)

References 63 publications

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“…To negotiate this hurdle, Ni is typically added in order to allow higher elemental contents of Al and Cr without losing the desired two-phase microstructure. For stabilizing the γ′-phase besides Niadditions also Ta, Ti, and Hf additions are suitable [13][14][15][16][17][18][19][20]. The investigation of model systems granted systematic understanding of the effect of Ni and Cr on the oxidation mechanisms in Co-base alloys [21].…”

Section: Introductionmentioning

confidence: 99%

On the High-Temperature Oxidation Behavior of a Ta-Containing Quaternary Co-Base Model Alloy System with γ/γ′-Microstructure - Influence of γ′-Volume Fraction, Surface State, and Heating Condition on Alumina Growth

et al. 2020

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The improvement of the high-temperature oxidation resistance remains an ambitious goal for the design of new γ/γ′-strengthened Co-base superalloys, since their oxidation resistance beyond 800 °C still ranks behind their Ni-base counterparts. To better understand the origin of the poor oxidation resistance at higher temperatures, this study focuses on early stages of oxidation of four quaternary (Co-Al-W-Ta system) Co-base model alloys with a two-phase γ/γ′-microstructure and varying γ′-volume fraction at 800 °C, 850 °C and 900 °C. Based on time-resolved isothermal gravimetric analysis (TGA) in synthetic air and detailed electron microscopic analysis, the role of the γ-channel width (or γ′-volume fraction), the surface preparation prior to exposure (polishing versus shot-peening), and the heating conditions (synthetic air versus argon) on protective alumina growth is elucidated. Firstly, for alloys of increased γ′-volume fractions slower oxidation kinetics prevailed. Secondly, the two-phase microstructure was found to decisively affect the propagation of the internal oxidation front at the early stages of oxidation. Thirdly, shot-peening prior to exposure together with a lack of oxygen availability during heating was identified to foster protective alumina growth, accompanied by TCP-phase formation in the substrate. The critical role of a high Al availability in the alloy for a rapid growth of protective alumina and the relating challenges in alloy development regarding, for example, phase stability in this relatively novel Co-base alloy class are discussed in detail.

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Section: Introductionmentioning

confidence: 99%

On the High-Temperature Oxidation Behavior of a Ta-Containing Quaternary Co-Base Model Alloy System with γ/γ′-Microstructure - Influence of γ′-Volume Fraction, Surface State, and Heating Condition on Alumina Growth

et al. 2020

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“…For example, addition of Ta to a Ni-based superalloys has been shown to reverse the partitioning of W from the γ' phase into the γ precipitate [59]. Similarly, in Co-based superalloys, Cr addition leads to a similar effect on the Mo partitioning behavior [60]. These observations can serve as guiding principles for devising improved alloy doping concepts for high temperature applications.…”

mentioning

confidence: 92%

On the segregation of Re at dislocations in the γ' phase of Ni-based single crystal superalloys

Makineni

Kontis

et al. 2018

Materialia

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We report evidence of Re and Mo segregation (up to 2.6 at.% and 1 at.%) along with Cr and Co to the dislocations inside of γ' precipitates in a second generation Ni-based single crystal superalloy, after creep deformation at 750°C under an applied stress of 800 MPa. The observed segregation effects can be rationalized through bridging the solute partitioning behavior across the γ/γ' interface and the pipe diffusion mechanism along the core of the dislocation line. This understanding can provide new insights enabling improved alloy design. Tomography.Single crystal Ni-based superalloys have long been important engineering materials used in gas turbines and jet engines due to their superior creep, fatigue and oxidation properties at elevated temperatures [1][2][3][4][5][6][7]. These are associated with the two-phase microstructure, where a disordered face-centered cubic (FCC) γ matrix contains a high volume fraction of L1 2 ordered γ' precipitates, which have been considered initially as dislocation-free [3]. Many elements are typically added for solid solution strengthening of the γ matrix, such as W and Mo [8]. Re has attracted special attention due to the fact that additions of 2 to 6 wt.% Re significantly enhance the creep properties of Ni-based single crystal superalloys [1,3,[9][10][11]. How Re improves the creep properties is debated.The following possibilities have been suggested in the literature: (i) solid solution strengthening and distortions of the γ matrix lattice due to the large size of Re atoms [1,12], (ii) the slow diffusion rate of Re in Ni (slowest of all d-shell elements) [13,14], and (iii) the possible formation of Re clusters in the γ matrix that might hinder dislocation movement [15][16][17][18]. However, these Re

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“…First of them is based on tungsten addition and Co 3 (Al,W) phase as a strengthening structural element. The second group is called W-free alloys and consists of other high melting point elements such as Mo, Nb and Ta as elements forming the desirable Co 3 (Al,X) phase [3,4].…”

Section: Introductionmentioning

confidence: 99%

Thermal analysis of W-free Co–(Ni)–Al–Mo–Nb superalloys

Migas

Moskal

Maciąg

2020

J Therm Anal Calorim

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In this investigation, the thermal analysis of W-free cobalt-based superalloys based on Co–Al–Mo–Nb and Co–Ni–Al–Mo–Nb systems was performed. The analysis was performed at different stages of heat treatment process. The differential thermal analysis (DTA) was utilized for the determination of characteristic temperatures related to microstructural changes. First of all, the DTA analysis was carried out for discussing as-cast alloys in the temperature range of 40–1500 °C. The results showed thermal effects connected with melting and important order–disorder transition. The temperature range of 1200–1250 °C was chosen for performance of a first heat treatment operation for the investigated alloys. Specimens were annealed at selected temperature for 5 h. The microstructure of alloys after solution heat treatment was analyzed as well. Afterward, the solutionized specimens were subjected to the further thermal analysis in order to select the aging temperature according to the order–disorder transformation related to formation of γ′ phase with overall formula Co3(Al,X). Five aging variants were performed in the temperature range of 800–1000 with a step of 50 °C. After each stage of heat treatment, SEM/EDS analysis and hardness measurements were performed.

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Effect of Cr addition on γ–γ′ cobalt-based Co–Mo–Al–Ta class of superalloys: a combined experimental and computational study

Cited by 63 publications

References 63 publications

On the High-Temperature Oxidation Behavior of a Ta-Containing Quaternary Co-Base Model Alloy System with γ/γ′-Microstructure - Influence of γ′-Volume Fraction, Surface State, and Heating Condition on Alumina Growth

On the High-Temperature Oxidation Behavior of a Ta-Containing Quaternary Co-Base Model Alloy System with γ/γ′-Microstructure - Influence of γ′-Volume Fraction, Surface State, and Heating Condition on Alumina Growth

On the segregation of Re at dislocations in the γ' phase of Ni-based single crystal superalloys

Thermal analysis of W-free Co–(Ni)–Al–Mo–Nb superalloys

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