铁基合金马氏体的形核与长大

NUCLEATION AND GROWTH OF FERROUS MARTENSITES

本文使用光学和电子显微镜低温台对Fe-Mn-C合金中ε马氏体的形成过程和Fe-Ni-C合金中蝶状、透镜状、薄片状和复片状马氏体的形成过程进行了原位观察。本文实验结果指出;ε马氏体由4—5个层错重叠形成,证实了Olson和Cohen提出的层错化模型;薄片状马氏体优先在晶界和三角晶界处形核,初始长大形态(表面浮突)为细针状;观察到透镜状马氏体由薄片状向两侧加厚而形成,提出了相变孪晶长大受阻时,半共格孪晶界面位错可经位错分解反应发射出a/2[111]b=a_0/2[101]_f全位错,提供薄片状马氏体由孪生切变向滑移切变转换所需的位错源。

In situ observations of the nucleation and growth of ferrous marten- sites, including ε-, lenticular, butterfly, thin-plate and composite-plate ones at low temperature stage on optical or transmission electron microscope were carried out. The results confirmed the faulting model for the formation of ε-martensite proposed by Olson and Cohen. The grain boundaries and triple points are the favourable nu- cleation sites for the thin plates, and their surface relief grown initially like a small needle. The lenticular martensite was observed as two stages of formation. According to the dislocation resolving reaction: a/6[111]_b→a/3[111]_b+a/2[111]_b, the emission dislocation(b=a/2[111]_b) acting as the dislocation soulce for the transition of lattice invariant shear from twinning to slip was proposed.