The synchronous improvement of strength and plasticity (SISP) in new Ni-Co based disc superalloys by controling stacking fault energy

Abstract

It is a great challenge to improve the strength of disc superalloys without great loss of plasticity together since the microstructures benefiting the strength always do not avail the plasticity. Interestingly, this study shows that the trade-off relationship between strength and plasticity can be broken through decreasing stacking fault energy (SFE) in newly developed Ni-Co based disc superalloys. Axial tensile tests in the temperature range of 25 to 725 °C were carried out in these alloys with Co content ranging from 5% to 23% (wt.%). It is found that the ultimate tensile strength (UTS) and uniform elongation (UE) are improved synchronously when microtwinning is activated by decreasing the SFE at 650 and 725 °C. In contrast, only UTS is improved when stacking fault (SF) dominates the plastic deformation at 25 and 400 °C. These results may be helpful for designing advanced disc superalloys with relatively excellent strength and plasticity simultaneously.

Refining Micron-Sized Grains to Nanoscale in Ni-Co Based Superalloy by Quasistatical Compressive Deformation at High Temperature

“…MT is a kind of special deformation twin that has a thickness of 4-50 atom layers, which play an important role in the deformation mechanisms of low SFE superalloys. It is reported that MTs could synchronously improve the strength and plasticity by acting both as dislocation blockers and dislocation slip planes in Ni-Co-based superalloys during tensile tests [13]. It has been well documented that MTs were generally introduced by severe plastic deformation that applied high strain rate and deformation amount at a low temperature [25,26].…”

“…In the low-SFE superalloys, it was proved that microtwins (MTs) could be introduced during tensile deformation [12]. Furthermore, the ultimate tensile strength and uniform elongation were improved synchronously because microtwinning was activated in superalloys with decreased SFE at 650 and 725 • C [13]. When deformation occurred at higher strains, nanograins (NGs) were found to be produced in the superalloys deformed at a high temperature and low strain rate, which resulted in higher flow stress [14].…”

L12‐Strengthened Co‐Rich Alloys for High‐Temperature Structural Applications: A Critical Review

“…The increased Co:Ni ratio decreases the stacking fault energy of the L1 2 ‐strengthened superalloys, which promotes stacking fault formation during room‐temperature deformation. [ 66 ] As a result of the high‐density stacking faults formation, both the tensile strength and uniform elongation can be simultaneously improved. Moreover, the outstanding strength‐ductility combination has also been achieved in the Co–28.8Ni–10.0Al–10.2Cr–2.1Ti–2.2Ta–2.1Mo–1.5Nb multicomponent Co‐rich alloy, which demonstrates a tensile strength over 1 GPa together with a uniform elongation over 20% at room temperature.…”

“…The high‐temperature tensile properties also benefit from the increased Co:Ni ratio. [ 66 ] The profuse microtwinning formation contributes to the improved work‐hardening capacity and associated enhanced ultimate tensile strength at high temperature (over 1.2 GPa at 704 °C). Similarly, a newly developed Co‐rich superalloy with a composition of Co–37.6Ni–4.1Al–8.8W–14.0Cr–1.5Ti–0.5Ta–0.028C–0.009B–0.05Zr (wt%) also exhibited an outstanding high‐temperature strength.…”

Effects of Ultra-Low Temperatures on the Mechanical Properties and Microstructure Evolution of a Ni-Co-Based Superalloy Thin Sheet during Micro-Tensile Deformation

“…The National Institute for Materials Science of Japan successfully developed the TMW series Ni-Co-based superalloys first by reducing SFE [8]. Compared with the stronger cast-forged U720Li superalloy, the temperature-bearing capacity of this Ni-Co-based superalloy can be increased by 30 • C. The mechanical properties and structural stability of Ni-Co-based superalloys are better than those of the U720Li superalloy, which is expected to become a key material for hot-end components [9][10][11][12]. With the unstoppable trend of product miniaturization in many fields such as aerospace, the nuclear industry, weapons equipment, and energy, precise plastic forming technology of Ni-Co-based superalloy micro components is a key task that needs to be solved urgently.…”