Abstract
The present work investigated the composition evolution of the TMS series of Ni-base single crystal (SC) superalloys in light of the cluster formula approach systematically. The cluster formula of SC superalloys could be expressed with {[}overline{{{text{Al}}}} {-} overline{{{text{Ni}}}} 12{](}overline{{{text{Al}}}} {, }overline{{{text{Cr}}}} {)}m, in which all the alloying elements were classified into three groups, Al series (overline{{{text{Al}}}}), Cr series (overline{{{text{Cr}}}}), and Ni series (overline{{{text{Ni}}}}). It was found that the total atom number (Z) of the cluster formula units for TMS series of superalloys varies from Z ~ 17 to Z ~ 15.5, and then to Z ~ 16 with the alloy development from the 1st to the 6th generation, in which the superalloys with prominent creep resistance possess an ideal cluster formula of {[}overline{{{text{Al}}}} {-} overline{{{text{Ni}}}} 12{](}overline{{{text{Al}}}} 1.5overline{{{text{Cr}}}} 1.5{)} with Z = 16. Similar tendency of composition evolution also appears in the PWA and CMSX series of SC superalloys. Typical TMS series of superalloys with prominent creep properties generally exhibit a moderate lattice misfit of γ/γ′ which could render alloys with appropriate particle size of cuboidal γ′ precipitates to acquire a maximum strength increment by precipitation strengthening mechanism. More importantly, the relationship between the lattice misfit (δ) of γ/γ′ and the creep rupture lifetime (tr) of superalloys was then established, showing a linear correlation in the form of lgtr–lg|δ|3/2 at both conditions of 900 °C/392 MPa and 1100 °C/137 MPa. Combined with the lattice misfit, the cluster formula approach would provide a new way to modify or optimize the compositions of Ni-base superalloys for further improvement of creep property.
Highlights
The present work investigated the composition evolution of the TMS series of Ni-base single crystal (SC) superalloys in light of the cluster formula approach systematically
Several computation-aided design methods have been applied into the development of Ni-base SC superalloys, such as PHACOMP28–30, New PHACOMP based on the d-electrons theory[31,32,33,34], ADP14,35, Multi-criteria Numerical Optimization[36,37], Alloys-by-Design[38,39], and so on
By exploring the composition rules of TMS series of Ni-base single crystal superalloys with the cluster formula approach and the influence of composition on the creep properties, several key points could be summarized as follows: (1) The cluster formula of TMS series of superalloys is expressed with the [Al−Ni12](Al,Cr)m, in which all the alloying elements are classified into three groups, Al series, Cr series, and Ni series
Summary
The present work investigated the composition evolution of the TMS series of Ni-base single crystal (SC) superalloys in light of the cluster formula approach systematically. Typical TMS series of superalloys with prominent creep properties generally exhibit a moderate lattice misfit of γ/γ′ which could render alloys with appropriate particle size of cuboidal γ′ precipitates to acquire a maximum strength increment by precipitation strengthening mechanism. The prominent high-temperature (HT) mechanical properties of Ni-base single crystal (SC) superalloys are primarily benefited from their unique coherent microstructure with cuboidal ordered L 12-γ′ (Cu3Au-type) nanoparticles precipitated in the face-centered-cubic (FCC) γ solid solution m atrix[1]. This kind of coherent microstructure strengthened by ordered phase is closely related to the lattice misfit (δ) between γ and γ′ phases that depends on their chemical compositions. The classical New PHACOMP was well developed by calculating the electronic structure of alloys with the DV-Xα molecular orbital method, in which the important parameter Md represents an average energy level of d orbitals of transition metals and is used to predict the phase stability of FCC-γ matrix and the precipitation of TCP phase[31,32,33,34]
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