Formation of L12-structured Ni3Si
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Nickel-23 at. pct Si produced by hot extrusion of canned powders is two phase above 1035 °C, consisting of particles of the nickel (silicon) solid solution in a complex silicide matrix, labeled β2 on the phase diagram. Transformation to the Ll2-structured β1-Ni3Si was examined at temperatures from 525 °C to 925 °C by both optical microscopy and transmission electron microscopy. Transformation to β1-Ni3Si was observed to occur by three different processes, namely, by precipitation within the Ni(Si) particles, by the peritectoid transformation Ni(Si) + β2 → β1, and by the eutectoid decomposition of β2, that is, through β2 → β1 + γNi31Si12. All of the transformations are consistent with the phase diagram. The β1 which formed both by precipitation and by the peritectoid transformation is coherent with the Ni(Si) solid solution. The peritectoid transformation appears to be interface controlled (at the coherent β1/β2 interface), as evidenced by the anisotropic fingerlike growth of the β1 into the β2 matrix.
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