Comparative study of the densification kinetics of the FCC phase Al0.3CoCrFeNi and BCC phase AlCoCrFeNi high-entropy alloys during spark plasma sintering

The densification kinetics of the FCC-matrix Al0.3CoCrFeNi and BCC-matrix AlCoCrFeNi HEAs at sintering temperatures ranging from 950 & DEG;C to 1050 & DEG;C are comparatively studied utilizing the steady-state creep model. The densification activation energy of the Al0.3CoCrFeNi and AlCoCrFeNi powder in their low-stress exponent stage is linearly fitted to be 264.91 and 220.99 kJ/mol, respectively. The densification mechanism of both the two HEAs in the low-stress exponent stage is proved to be atomic diffusion. However, the densification activation of the Al0.3CoCrFeNi in the high-stress exponent stage increases to 554.77 kJ/mol and the densification mechanism changes to creep. The densification activation energy of the AlCoCrFeNi in its high-stress exponent stage cannot be obtained by linear fitting because of the abnormal increase of the stress exponent at the sintering temperature of 1050 & DEG;C. The BCC-FCC transformation in the AlCoCrFeNi reduces its creep resistance because of different deformation behavior in BCC (dislocation cell) and FCC phase (cross-glide and twinning). As a result, dislocation density is higher in the FCC phase (4.3 x1013/m2) compared with the BCC phase (3.8 x1013/m2), which benefits the densification in the creep-controlled high-stress exponent stage. Furthermore, the stronger electromigration effect induced by a higher heating rate is demonstrated to further reduce the densification activation energy from 124.20 to 72.53 kJ/mol and accelerate densification in the diffusion-controlled heating period.

Automated summary

The densification kinetics of FCC-matrix and BCC-matrix high entropy alloys (HEAs) were studied at sintering temperatures ranging from 950°C to 1050°C. The densification activation energy in the low-stress exponent stage was linearly fitted to be 264.91 kJ/mol for Al0.3CoCrFeNi and 220.99 kJ/mol for AlCoCrFeNi. The densification mechanism in this stage was proved to be atomic diffusion. However, in the high-stress exponent stage, the densification activation energy for Al0.3CoCrFeNi increased to 554.77 kJ/mol and the densification mechanism changed to creep. The BCC-FCC transformation in AlCoCrFeNi reduced its creep resistance due to different deformation behavior in BCC and FCC phase. The research also demonstrated that a higher heating rate induced a stronger electromigration effect, reducing the densification activation energy and accelerating densification.