TY - JOUR
T1 - Phosphorous behavior and its effect on secondary phase formation in high refractory content powder-processed Ni-based superalloys
AU - Antonov, Stoichko
AU - Isheim, Dieter
AU - Seidman, David N.
AU - Tin, S.
N1 - Funding Information:
None. Financial support for this work was provided by Rolls-Royce Corporation. The authors would also like to thank Dr. Eugene Sun of Rolls-Royce Corporation for supplying the material and financial support. This work made use of the EPIC, Keck-II, and/or SPID facility(ies) of Northwestern University's NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the MRSEC program (NSF DMR-1121262) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. Atom-probe tomography was performed at the Northwestern University Center for Atom-Probe Tomography (NUCAPT). The LEAP tomograph at NUCAPT was purchased and upgraded with grants from the NSF-MRI (DMR-0420532) and ONR-DURIP (N00014-0400798, N00014-0610539, N00014-0910781, N00014-1712870) programs. NUCAPT received support from the MRSEC program (NSF DMR-1720139) at the Materials Research Center, the SHyNE Resource (NSF ECCS-1542205), and the Initiative for Sustainability and Energy (ISEN) at Northwestern University.
PY - 2019/9
Y1 - 2019/9
N2 - The behavior of phosphorous and its effect on the microstructure of a powder-processed, high refractory content, Ni-based superalloy was studied and compared to a P-free variant. Transmission electron microscopy and atom probe tomography were used to identify the crystal structure of the five topologically close packed (TCP) and geometrically close packed (GCP) phases that formed, assess phase compositions, and determine any elemental segregation to phase boundaries. The results revealed strong phosphorous segregation to grain boundaries, moderate solubility in TCP and MC phases, limited solubility in the γ matrix and no solubility in the γ′ phase or any other Ni3X type GCP phases. The phosphorus segregation to the grain boundaries of the P-doped alloy lowered the incipient melting temperature, thereby eliminating the processing window, and led to the formation of (Ni,Co,Cr,P)2(Nb,Mo) laves phases along grain boundaries during supersolvus heat treatment. Interestingly, APT revealed segregation of P to Al2O3 oxide surfaces, explaining the frequent observation of laves precipitates nucleating on such impurities. Due to the low stability of the C14–Ni2Nb laves phase, it was prone to phase separation, and served as the nucleation point for μ, intergrown η/δ, and Nb3P phosphide phases.
AB - The behavior of phosphorous and its effect on the microstructure of a powder-processed, high refractory content, Ni-based superalloy was studied and compared to a P-free variant. Transmission electron microscopy and atom probe tomography were used to identify the crystal structure of the five topologically close packed (TCP) and geometrically close packed (GCP) phases that formed, assess phase compositions, and determine any elemental segregation to phase boundaries. The results revealed strong phosphorous segregation to grain boundaries, moderate solubility in TCP and MC phases, limited solubility in the γ matrix and no solubility in the γ′ phase or any other Ni3X type GCP phases. The phosphorus segregation to the grain boundaries of the P-doped alloy lowered the incipient melting temperature, thereby eliminating the processing window, and led to the formation of (Ni,Co,Cr,P)2(Nb,Mo) laves phases along grain boundaries during supersolvus heat treatment. Interestingly, APT revealed segregation of P to Al2O3 oxide surfaces, explaining the frequent observation of laves precipitates nucleating on such impurities. Due to the low stability of the C14–Ni2Nb laves phase, it was prone to phase separation, and served as the nucleation point for μ, intergrown η/δ, and Nb3P phosphide phases.
KW - Atom probe tomography (APT)
KW - Laves phases
KW - Ni-based superalloys
KW - Phosphorous
KW - Powder Processing
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U2 - 10.1016/j.mtla.2019.100423
DO - 10.1016/j.mtla.2019.100423
M3 - Article
AN - SCOPUS:85070197351
VL - 7
JO - Materialia
JF - Materialia
SN - 2589-1529
M1 - 100423
ER -