FORMATION OF THE (γ/α) - INTERPHASE BOUNDARIES IN FeCrNi ALLOYS BY A DIFFUSION BONDING METHOD

Characteristics of the interphase boundary in two-phase (γ/α)-stainless steel couples produced by a solid-solid diffusion method, starting from Fe-30%Cr (α-phase) and Fe-15%Cr-15%Ni (γ-phase) alloys, have been described. Interphase boundaries between a parent (γ-phase and a transformed (α-phase have been found to be essentially planar and no special structual defects have been detected, excepting a so-called "diffusion-induced twins" grown often in the (γ-phase, similar to those found in the diffusion couples of α/β-brass bicrystals by one of the authors and his colleagues / 1 /. It is found that the transformed α(αn)-phase inherits the crystallographic orientation of the original α(α0)-phase in a similar manner to GRAIN GROWTH. However, if the bonding orientation relation is set to be a near Kurjumov- Sachs relation, NUCLEATION of the phase transformation occurs and the resulting orientation relations become closer to the preferencial one. The present results suggest that the critical condition for the occurrence of the nucleation is attributable to the interfacial energy criterion on the (γ/α)-interface and the grain boundary between the α0 and αn-phases