MORPHOLOGY TRANSITIONS OF DEFORMATION-INDUCED THIN-PLATE MARTENSITE IN FE-NI-C ALLOYS

The morphology and crystallography of deformation-induced martensites formed during isothermal tensile tests in Fe-30Ni-0.34C and Fe-25Ni-0. 66C alloys were investigated by means of optical, transmission electro n and scanning electron microscopy. Transitions in morphology from thi n plate to coupled plate, to lenticular coupled-plate martensite and f rom thin plate to lenticular to compact martensite have been observed with increasing deformation. Stress favours the growth of martensite w hen concurrent plastic strain allows accommodation of macroscopic tran sformation strains and the change of the Bain strain accommodation mec hanism. Mobile dislocations and emission dislocations are directly rel ated to the change of the Bain strain accommodation mechanism from twi nning to slip. (C) 1998 Acta Metallurgica Inc. Published by Elsevier S cience Ltd. All rights reserved.