By high temperature microscopy, we conducted in-situ observation on the evolution of peritectic melting of YBa2Cu3O7−y thin films (denoted as the α phase). As the α phase was highly superheated above a critical temperature, we found that a non-equilibrium phase transition occurred. An unexpected metastable Y2O3 phase (denoted as the γ phase), resulted from the decomposition of the α film, nucleated preferentially to the stable phase of Y2BaCuO5 (denoted as the β phase). Both high superheating capability of the α film and low interface energy of the γ phase with substrates are responsible for the metastable phase transition in this work.
A strain-induced reverse phase transformation from a hexagonal close-packed phase to a face-centered cubic phase was observed under tension at room temperature in electrodeposited nanocrystalline Co-Ni alloys with an average grain size of 15 nm. Such reverse phase transformation was previously observed only on heating. Investigation by transmission electron microscopy suggests a close relationship between the reverse phase transformation and grain growth during the tensile deformation.
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