On the faulting and twinning mediated strengthening and plasticity in a γʹ strengthened CoNi-based superalloy at room temperature

Pandey, P and Heczko, M and Khatavkar, N and Mazumder, N and Sharma, A and Singh, A and Mills, MJ and Chattopadhyay, K (2023) On the faulting and twinning mediated strengthening and plasticity in a γʹ strengthened CoNi-based superalloy at room temperature. In: Acta Materialia, 252 .

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Abstract

Microscopic defects and their mutual interactions are fundamentally important in deciding the load carrying capacity of structural materials. In this context, the present work reports an unprecedented precipitate shearing mechanism in CoNi-based superalloys at room temperature where L12 ordered γʹ precipitates are embedded within a disordered CoCrNi-rich matrix. A combined electron channelling contrast imaging (ECCI) and scanning transmission electron microscopy (STEM) analysis revealed stacking fault (SF) and SF coupled nano-twin formation that rendered a significant work hardening rate. The observed twinning induced plasticity (TWIP) effect correlates with an excellent combination of yield strength, ultimate tensile strength (UTS) and plasticity of 910 ± 30 MPa, 1360 ± 40 MPa and ∼ 18.5 (%), respectively, as exhibited by the peak aged Co-30Ni-12Cr-7Al-4Ti-2Nb-0.006B alloy at room temperature. Rigorous center of symmetry (COS) analysis on atomic resolution STEM images from the deformed samples unambiguously establishes precipitate shearing via single a/6⟨112⟩{111} partial dislocations resulting in twin formation, succeeding the intrinsic stacking fault (ISF) and complex stacking fault (CSF) of γ and γʹ, respectively. Through thermodynamic and first principles density functional theory calculations, it is demonstrated that the experimentally observed deformation mechanism is directly correlated with the negative stacking fault energy of γ matrix and low CSF energy of the γʹ precipitates. Based on these new findings, the present work demonstrates the flexibility of tuning the composition of CoCrNi containing superalloys to widen the alloy spectrum for designing alloys with improved properties.

Item Type:	Journal Article
Publication:	Acta Materialia
Publisher:	Acta Materialia Inc
Additional Information:	The copyright for this article belongs to Acta Materialia Inc.
Keywords:	Aluminum alloys; Binary alloys; Chromium alloys; Cobalt alloys; Density functional theory; High resolution transmission electron microscopy; Nickel alloys; Niobium alloys; Plasticity; Scanning electron microscopy; Shearing; Stacking faults; Strain hardening; Superalloys; Temperature; Ternary alloys; Titanium alloys, Complex stacking faults; Coni-based superalloy; Fault energy; matrix; Microscopic defects; Mutual interaction; Scanning transmission electron microscopy; Stacking fault energy; Twin formation; γ' precipitates, Tensile strength
Department/Centre:	Division of Chemical Sciences > Materials Research Centre Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	01 Jun 2023 05:42
Last Modified:	01 Jun 2023 05:42
URI:	https://eprints.iisc.ac.in/id/eprint/81544

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