The nucleation and growth of η phase in nickel-based superalloy during long-term thermal exposure

TY - JOUR

T1 - The nucleation and growth of η phase in nickel-based superalloy during long-term thermal exposure

AU - Liu, Gang

AU - Xiao, Xueshan

AU - Véron, Muriel

AU - Birosca, Soran

PY - 2020/2/15

Y1 - 2020/2/15

N2 - The microstructure degradation and subsequent phase transformations in Waspaloy nickel-based superalloy during thermal exposure at 780 °C for 10,000 h were investigated. Two paths of η phase formation in the centre of extra-large γ’ (EL-γ’) following the formation of EL-γ’ were observed: (i) η phase directly precipitated within EL-γ’ when the coalescence of γ’ reached a critical stage; (ii) η phase precipitated at the interface of small size MC carbide and EL-γ’, with both MC and η embedded inside EL-γ’. The phase transformation process including the formation of EL-γ’ were experimentally observed and the formation sequences were schematically suggested. Two criteria of η formation and growth within EL-γ’ were established: (i) stacking faults formation in the nucleation site and (ii) sufficient atom diffusion during nuclei growth. The study of kinetics of η formation through two different paths revealed the critical role of small size carbides in promoting η nucleation and growth. It is concluded that η formation may be suppressed by controlling the size and density of MC carbides during materials processing.

AB - The microstructure degradation and subsequent phase transformations in Waspaloy nickel-based superalloy during thermal exposure at 780 °C for 10,000 h were investigated. Two paths of η phase formation in the centre of extra-large γ’ (EL-γ’) following the formation of EL-γ’ were observed: (i) η phase directly precipitated within EL-γ’ when the coalescence of γ’ reached a critical stage; (ii) η phase precipitated at the interface of small size MC carbide and EL-γ’, with both MC and η embedded inside EL-γ’. The phase transformation process including the formation of EL-γ’ were experimentally observed and the formation sequences were schematically suggested. Two criteria of η formation and growth within EL-γ’ were established: (i) stacking faults formation in the nucleation site and (ii) sufficient atom diffusion during nuclei growth. The study of kinetics of η formation through two different paths revealed the critical role of small size carbides in promoting η nucleation and growth. It is concluded that η formation may be suppressed by controlling the size and density of MC carbides during materials processing.

KW - MC-carbide

KW - Nickel-based superalloy

KW - Phase transformation

KW - Waspaloy

KW - η phase

UR - http://www.scopus.com/inward/record.url?scp=85078733702&partnerID=8YFLogxK

UR - https://cronfa.swan.ac.uk/Record/cronfa53128

U2 - 10.1016/j.actamat.2019.12.038

DO - 10.1016/j.actamat.2019.12.038

M3 - Article

AN - SCOPUS:85078733702

VL - 185

SP - 493

EP - 506

JO - Acta Materialia

JF - Acta Materialia

SN - 1359-6454

ER -