Here, we study strain und temperature induced phase transformation pathways in high entropy alloys (HEA) by aberration-corrected and in situ
scanning transmission electron microscopy (S/TEM). The bidirectional phase transformation (face-centered cubic (FCC) → hexagonal close packed (HCP) → FCC) in a transformation-induced plasticity (TRIP)-assisted high-entropy alloy (HEA) is explored by a combination of atomic resolution imaging and in situ
tensile straining. In a similar HEA, the temperature induced transformation from HCP to nanotwinned FCC and associated formation of nanocarbides at the nanotwin boundaries are investigated at atomic resolution by in situ
heating. We aim to reveal the atomic scale origins of phase transformations to guide the design of advanced HEAs with a unique combination of strength, ductility and thermal stability.