Composition rules of Ni-base single crystal superalloys and its influence on creep properties via a cluster formula approach

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 $${[}\overline{{{\text{Al}}}} {-} \overline{{{\text{Ni}}}} 12{](}\overline{{{\text{Al}}}} {, }\overline{{{\text{Cr}}}} {)}m$$ [ Al ¯ - Ni ¯ 12 ] ( Al ¯ , Cr ¯ ) m , in which all the alloying elements were classified into three groups, Al series ($$\overline{{{\text{Al}}}}$$ Al ¯ ), Cr series ($$\overline{{{\text{Cr}}}}$$ Cr ¯ ), and Ni series ($$\overline{{{\text{Ni}}}}$$ 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 $${[}\overline{{{\text{Al}}}} {-} \overline{{{\text{Ni}}}} 12{](}\overline{{{\text{Al}}}} 1.5\overline{{{\text{Cr}}}} 1.5{)}$$ [ Al ¯ - Ni ¯ 12 ] ( Al ¯ 1.5 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.

Composition formulas of solid-solution alloys derived from chemical-short-range orders

“…As demonstrated in references 7,14,15 , compositions of commonly used industrial alloys such as Cu alloys, Al alloys, stainless steels, and Ni-based superalloys fall close to the model predictions, validating the presence of simple chemical units in metallic alloys and the generality of the cluster formulism. Our recent work 16 shows that the model also applies in high-entropy alloys, after appropriate elemental classification.…”

Comparative Analysis between 5th and 6th Generation Superalloys and Previous Generation Superalloys

“…Another study [24] investigated the composition rules for Ni-superalloys and what their impact is on the alloys' creep properties. In order to study the composition of the alloy, a uniform cluster formula for [Al-Ni12](Al, Cr)m was developed.…”

“…One study [24] examined in detail how the composition of certain alloying elements influences the creep properties of Ni-superalloys and establishes superiority in the case of 5 th and 6 th gen Ni-superalloys. In order to study the composition of the alloy, a uniform cluster formula for [Al-Ni12] (Al, Cr) m was developed.…”

Critical Raw Materials Saving by Protective Coatings under Extreme Conditions: A Review of Last Trends in Alloys and Coatings for Aerospace Engine Applications

“…Up to now, sixth generation superalloys of the TMS series have been developed by finely tuning the alloying elements in order to enhance the oxidation-resistance at high temperature and improve the creep strength. To this aim, computation-aided design methods have been developed [ 57 , 58 ]. The addition of a small amount of Si element (<0.5 wt.%) could help the formation of compact oxide scales, while excessive Si amount is detrimental to the mechanical property since it could accelerate the precipitation of TCP phases.…”

“…The addition of Mo element (~0.6 wt.%) could improve the thermomechanical fatigue property of alloys. Unfortunately, all these improvements are at the expense of the creep rupture lifetime of the superalloy [ 57 ].…”