Improving the intermediate- and high-temperature strength of L12-Co3(Al,W) by Ni and Ta additions

The effects of Ni and Ta additions on the mechanical properties in the L1(2) compound Co-3(Al,W), the strengthening phase of Co-based superalloys, have been investigated by compression tests between room temperature and 1000 ?, in order to elucidate the effects of stability of the L1(2) phase on the mechanical properties. The additions of Ni and Ta, both of which are L1(2)-stabilizers that increase the L1(2) solvus temperature, increase the yield strength at intermediate and high temperatures. The strength increase is shown to be more significant as the amount of additions of these elements and thereby the stability of the L1(2) phase increases. Two factors account for the strength increase at intermediate temperatures: The reduction of the onset temperature of yield stress anomaly (YSA-onset) due to the increased complex stacking fault (CSF) energy and the increase in both the base strength and the intensity of the yield stress anomaly associated with an increased anti-phase boundary (APB) energy on (111) planes. The strength increase at high temperatures, on the other hand, arises from the increase in the peak temperature due to the increased L1(2) solvus temperatures. The increased strength of the L1(2) phase due to a higher phase stability thus partly accounts for the improved creep strength of Co-based superalloys upon alloying with Ni and Ta. (c) 2022 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

Automated summary

The effects of Ni and Ta additions on the mechanical properties of Co-based superalloys were investigated. The additions of Ni and Ta increased the yield strength at intermediate and high temperatures by increasing the stability of the L1(2) phase. The strength increase at intermediate temperatures can be attributed to the increased complex stacking fault energy and the increased anti-phase boundary energy on (111) planes. The strength increase at high temperatures is mainly due to the increased L1(2) solvus temperatures.