Distinctive yield behavior of low-density Co-Ni-Al-V-Ti-Ta superalloy designed by CALPHAD

Low-density superalloys often exhibit low yield strength in the intermediate temperature range (300-650 °C). To enhance yield performance in this range, the CALPHAD method was used to design a new Co-based superalloy. The Co-30Ni-10Al-3V-6Ti-2Ta alloy, designed based on γ′ phase dissolution temperature and phase fraction, was synthesized via arc melting and heat treatment. Phase transition temperatures, microstructure evolution, and high-temperature mechanical properties were characterized by differential scanning calorimetry, scanning electron microscopy, dual-beam TEM, and compression tests. Results show that the alloy has low density (8.15 g/cm³) and high γ′ dissolution temperature (1234 °C), along with unique yield strength retention from room temperature to 650 °C. The yield strength anomaly (YSA) is attributed to high stacking fault energy and activation of the Kear-Wilsdorf locking mechanism, contributing to superior high-temperature stability of the alloy. The yield strength of this alloy outperforms other low-density Co-based superalloys in the temperature range of 23-650 °C.