The characteristics of Umklapp transformation in Fe-Ni alloy containing 31%Ni were clarified through various experiments. (1) The Umklapp process is characterized by a burst phenomenon. (2) Great kinetic energy accompanied by the umklapp process can make a martensite leaf propagate into a temperature range higher than the usual γ → α transformation temperature in a single crystal with temperature gradient. (3) The 1st burst temperature is scattered statistically in a wide range of temperature. (4) The transformation amounts produced by the 1st burst increases with the degree of supercooling.
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