Influence of elevated Co and Ti levels on polycrystalline powder processed Ni-base superalloy

Jones, Nicholas; Christofidou, Katerina A.; Mignanelli, P. M.; Minshull, J. P.; Hardy, Mark; Stone, H.J.

doi:10.1179/1743284714y.0000000509

Cited by 32 publications

(20 citation statements)

References 31 publications

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“…However, care must be taken as prolonged exposures at 800°C were found to cause the precipitation of the r phase in Alloy B, which is known to reduce the creep performance of similar alloys. [16] In order to further elucidate the mechanisms governing the tensile and creep behavior of the developmental alloys, and assess the applicability of current models to novel alloy compositions, modeling of the mechanical properties was performed, and the data were compared to the experimental results. The model described by Parthasarathy et al [33] was used in the predictions for the yield strength of the alloys.…”

Section: Discussionmentioning

confidence: 99%

“…Although the creep life of the modified alloys was found to deteriorate when tested at 750°C and 460 MPa as a result of the precipitation of the TCP r phase along the grain boundaries. [16] Consequently, microstructural stability, and in particular the propensity of the alloys towards the precipitation of the r phase, was another key objective considered throughout the development of these alloys. In order to mitigate the detrimental effects on phase stability observed as a result of the increased Co level, the concentrations of the known r phase forming elements Cr and Mo were reduced.…”

Section: Alloy Design Methodologymentioning

confidence: 99%

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On the Effect of Nb on the Microstructure and Properties of Next Generation Polycrystalline Powder Metallurgy Ni-Based Superalloys

Christofidou

Hardy

et al. 2018

Metall Mater Trans A

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The effect of Nb on the properties and microstructure of two novel powder metallurgy (P/M) Ni-based superalloys was evaluated, and the results critically compared with the Rolls-Royce alloy RR1000. The Nb-containing alloy was found to exhibit improved tensile and creep properties as well as superior oxidation resistance compared with both RR1000 and the Nb-free variant tested. The beneficial effect of Nb on the tensile and creep properties was due to the microstructures obtained following the post-solution heat treatments, which led to a higher γ′ volume fraction and a finer tertiary γ′ distribution. In addition, an increase in the anti-phase-boundary energy of the γ′ phase is also expected with the addition of Nb, further contributing to the strength of the material. However, these modifications in the γ′ distribution detrimentally affect the dwell fatigue crack-growth behavior of the material, although this behavior can be improved through modified heat treatments. The oxidation resistance of the Nb-containing alloy was also enhanced as Nb is believed to accelerate the formation of a defect-free Cr2O3 scale. Overall, both developmental alloys, with and without the addition of Nb, were found to exhibit superior properties than RR1000.

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Section: Discussionmentioning

confidence: 99%

Section: Alloy Design Methodologymentioning

confidence: 99%

On the Effect of Nb on the Microstructure and Properties of Next Generation Polycrystalline Powder Metallurgy Ni-Based Superalloys

Christofidou

Hardy

et al. 2018

Metall Mater Trans A

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“…In addition, these alloys also include a range of other elemental additions to further improve their properties. Recently, elevated levels of Co and Ti have been shown to be beneficial, providing improved high temperature strength and creep resistance [1,2]. However, in addition to their mechanical performance, the environmental resistance of these alloys is also critical, as surface degradation can accelerate fatigue crack initiation during high temperature exposure, leading to premature failure [3][4][5].…”

Section: Introductionmentioning

confidence: 99%

The Oxidation Behaviour of Alloys Based on the Ni–Co–Al–Ti–Cr System

et al. 2015

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The isothermal oxidation behaviour of a series of quinary Ni-Co-AlTi-Cr alloys were studied at 800°C. Alloys with higher Cr concentrations exhibited lower mass gain after 100-h exposure, as did the alloys richest in Ni and Al for a given Cr concentration. Extensive internal oxidation and nitridation was also observed in all alloys, except those containing the highest concentrations of Ni and Al. All alloys studied generated continuous chromium oxide layers, beneath which alumina particles were observed. Compositional analysis of the subscales identified shallower Cr concentration gradients in alloys containing equiatomic levels of Ni and Co, suggesting increased availability of Cr in the alloy. Thermodynamic calculations confirmed that these alloys contained higher concentrations of Cr in their c matrices as a result of a combination of both the elemental partitioning behaviour and the increased mole fraction of c 0 precipitates forming in the alloy.

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“…Such modifications were shown to confer benefits to both the strength and microstructural stability of both cast & wrought [47][48][49][50][51] and powder processed [52,53] alloys. In parallel, fundamental studies of the underpinning Ni -CoAl -Ti system were performed and determined that the A1 -L1 2 two-phase field is continuous between Ni -Ni 3 Al and Co -Co 3 Ti [54,55].…”

Section: Introductionmentioning

confidence: 99%

The microstructure and hardness of Ni-Co-Al-Ti-Cr quinary alloys

Christofidou

Jones

Pickering

et al. 2016

Journal of Alloys and Compounds

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The effects of Ni:Co and Al:Ti ratios on the room temperature microstructure, hardness and lattice parameter of twenty-seven quinary Ni-Co-Al-Ti-Cr alloys have been evaluated. All of the alloys exhibited a uniform γ-γ′ microstructure. Differential scanning calorimetry (DSC) showed that the liquidus and solidus temperatures of the alloys, increase with greater Al:Ti ratios, decrease with Cr concentration and remained largely unchanged with respect to the Ni:Co ratio. Neutron diffraction measurements of the γ and γ′ lattice parameters revealed that the lattice misfit in all of the alloys was positive and increased with Ti concentration (i.e. lower Al:Ti ratio) regardless of the concentration of Cr, or the ratio of Ni:Co. Importantly, alloys with a Ni:Co ratio of 1:1, were found to have consistently greater lattice misfits than alloys with Ni:Co ratios of either 1:3 or 3:1. The measured lattice misfits were found to be strongly correlated with the Vickers hardness of the alloys, suggesting that lattice misfit plays a key role in the strengthening of γ-γ′ alloys of this type.

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Influence of elevated Co and Ti levels on polycrystalline powder processed Ni-base superalloy

Cited by 32 publications

References 31 publications

On the Effect of Nb on the Microstructure and Properties of Next Generation Polycrystalline Powder Metallurgy Ni-Based Superalloys

On the Effect of Nb on the Microstructure and Properties of Next Generation Polycrystalline Powder Metallurgy Ni-Based Superalloys

The Oxidation Behaviour of Alloys Based on the Ni–Co–Al–Ti–Cr System

The microstructure and hardness of Ni-Co-Al-Ti-Cr quinary alloys

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