High Pressure and High Temperature Exploration of Phase Transformations in Eutectic High Entropy Alloys

Additively manufactured high-entropy alloys are of interest because of their unique combination of high yield strength and large ductility achieved with far-from-equilibrium crystalline phases and micro/nanostructure morphology. This talk with report on the phase transformation and thermal equation of state of the eutectic high-entropy alloys (EHEAs) Al18Co20Cr10Fe10Ni40W2, and Al16.4Co16.4Cr16.4Fe16.4Ni34.4 produced by laser powder-bed fusion (L-PBF). Both EHEAs were studied in diamond anvil cells of pressures over 300GPa using angular dispersive x-ray diffraction (XRD) and in a large-volume Paris–Edinburgh cell using energy-dispersive XRD of temperatures up to 1723K at below 10GPa. The initial dual-phase nanolamellar face-centered cubic (FCC) and body-centered cubic (BCC) structure of each EHEA transforms into a single FCC phase under high pressure, with the BCC-to-FCC phase transformation completing under 20GPa. The FCC phase remained stable up to pressures over 300GPa. The measured thermal equation of state for the FCC phase of the EHEAs is presented alongside melt and recrystallization spectra. The BCC-to-FCC phase transition completion pressure is correlated with the nanolamellae thickness of the BCC layer in the transformation at ambient temperature.