Reclassification of phase transformation by growth mechanism alone is made in which equilibrium reaction occurs by volume diffusion, massive by interface diffusion and martensite by shear process. Based on this new classification, even at the slower cooling than specified before in the substitutional alloys, massive is proposed to occur. And any non-martensitic polymorphic change in a pure element is always massive irrespective of the degree of slow cooling.
The transformation form gamma to alpha during cooling a liquid phase sintered Fe-50wt.% Cu alloy at 100℃/min is proposed to be massive, judged from the microstructural features such as "boundary crossing". The so called "scallop edge" structure after resintering the Fe-Cu alloy is shown to be developed not by the sintering temperature variation but by the newly formed grain boundaries by massive transformation. And these grain boundaries are proposed to form between 650℃ and 700℃ during cooling at 100℃/min in agreement with the Rasanen's result of massive start temperature of 675℃ in the Fe-Cu alloy. After liquid phase sintering, isothermal holding at 780℃ results in the microstructure of "boundary crossing". This result can be interpreted as the depletion of Cu in the Fe rich grain by precipitation of epsilon phase with the resultant change of the composition from the metastable gamma region to the metastable alpha phase region. This result also suggests that the eutectoid reaction in the Fe-Cu alloy is not cooperative but occurs like a precipitate reaction.
