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

Christofidou, Katerina A.; Jones, Nicholas; Pickering, Ed; Flacau, Roxana; Hardy, MC; Stone, Howard J.

doi:10.1016/j.jallcom.2016.07.159

Cited by 30 publications

(15 citation statements)

References 71 publications

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“…However, while thermodynamic modeling can provide useful insights into the relative microstructural behavior of alloys, the complexity of the compositions considered, along with the relative kinetics of precipitation of the phases forming complicate the interpretation and fidelity of the results, and hence, care must be taken when such tools are utilized. [30] III. EXPERIMENTAL Powders for the development compositions and RR1000 were produced at ATI Powder Metals (Robinson) in Pittsburgh, PA.…”

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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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: 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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“…A further, less established benefit of Co is its ability to influence the size of secondary c 0 particles, particularly those in intergranular locations. For a given cooling rate from super-solvus solution heat treatment, increasing Co content reduces the size of secondary c 0 precipitates [33].…”

Section: Alloy Designmentioning

confidence: 99%

Developing Alloy Compositions for Future High Temperature Disk Rotors

Hardy

Argyrakis

Kitaguchi

et al. 2020

The Minerals, Metals &Amp; Materials Series

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Two new alloy compositions for possible disk rotor applications have been examined. Both were intended to have higher c 0 content than the existing alloy, RR1000, and be produced using powder metallurgy and isothermal forging to enable forgings to show a consistent coarse grain microstructure. Small pancake forgings of the new alloys and RR1000 were made and from these, blanks were cut, solution heat treated, cooled at measured rates and aged. Results of screening tests to understand the tensile, creep and dwell crack growth behavior, oxidation resistance and phase stability of these new alloys and coarse grain RR1000 are reported. The development alloys were similar in composition but exhibited different tensile and creep properties, phase stability and resistance to oxidation damage. Despite attempts to minimize variation in microstructure from heat treatment, differences in c 0 size distribution were found to influence tensile and creep behavior. One of the new alloys (Alloy 2) showed improved yield and tensile strength compared to RR1000. Alloy 2 displayed similar initial creep strain behavior to RR1000 but superior resistance to subsequent creep damage, producing longer creep rupture lives. All of the alloys showed crack retardation at low stress intensity factor ranges (DK) from 3600 s dwell cycles at 700°C in air. This occurred whilst crack growth was intergranular. Alloy 1 was found to precipitate C14 Laves phase from long term exposure at 800°C. Like RR1000, r phase was not detected in the new alloys after 750 h at 800°C.

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“…It is however challenging to get the duplex FCC+L12 microstructure as a large amount of Fe is required and is not compatible with a high Cr content [38]. A significant number of Al-Co-Cr-Ni-Ti quinary alloys have also been investigated within the framework of (Ni,Co)-based superalloys [61,76]. It seems that extending from Ni-based compositions to (Ni,Co)-based ones can positively impact HT properties [77].…”

Section: On the Alloying Strategy To Design Fcc+l12 Complex Concentrated Alloysmentioning

confidence: 99%

Study of the FCC+L12 two-phase region in complex concentrated alloys based on the Al–Co–Cr–Fe–Ni–Ti system

et al. 2020

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New face-centered cubic (FCC) multicomponent alloys designed through the high-entropy (HEA) concept and strengthened with L12 ordered precipitates are promising material solutions for high temperature (HT) structural applications. However, as the design strategy is based on multi-principal elements, the research of alloy compositions exhibiting a stable and well-controlled FCC+L12 microstructure at HT is particularly challenging. Among the critical issues, those relative to the extent and the stability of the FCC+L12 two-phase region in the wide compositional space have to be addressed. Here, we performed high-throughput Calphad calculations in the senary Al-Co-Cr-Fe-Ni-Ti system in the 800°C-1000°C range to screen alloy compositions exhibiting duplex FCC+L12 microstructures. From the 79 695 analyzed compositions, we show that roughly 6% of the total own duplex microstructure at 800°C and 1000°C. Calculations suggest that Cr and Fe additions destabilize the two-phase region. Interestingly we found that Fe is a good candidate to substitute Co or Ni in the FCC phase and potentially induce some solid solution strengthening effects. Finally, the present results allow to propose an original 2D visualization method of the two-phase FCC+L12 region in the complex compositional space. The method is based on the relative influence of the alloying elements on the formation of such microstructure. To assess the reliability of calculations, six alloys were designed and characterized. A good agreement is found between predictive calculations and experimental results except for Cr-and Al-free alloy compositions in the quaternary Co-Fe-Ni-Ti system, due to the absence of description of the τ phase with (Ni0.5Co0.5)3Ti composition in the selected thermodynamic database.

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

Cited by 30 publications

References 71 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

Developing Alloy Compositions for Future High Temperature Disk Rotors

Study of the FCC+L12 two-phase region in complex concentrated alloys based on the Al–Co–Cr–Fe–Ni–Ti system

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