Interphase-boundary structures and mechanical properties of two-phase ( / ) stainless steel bicrystals

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The morphology of two-phase ( / ) stainless steel couples, starting from Fe- 30Cr( -phase) and Fe-15Cr-15Ni( -phase) alloys produced by a solid-solid diffusion method has been investigated. Macroscopic units made of single crystals of the - and - phases (two-phase bicrystals) could be obtained. Interphase boundaries between a parent -phase and a transformed -phase have been found to be essentially planar and no special structual defects have been detected, excepting a so-called diffusion-induced twin faults grown often in the -phase due to the inevitable concentration gradient adjacent to the interphase boundary.It is found that the transformed ( _n)-phase generally inherits the crystallographic orien-tation of the original ( _o)-phase in a similar manner to "Grain growth", when the initial bonding orientation relation is arbitrary. However, if the bonding orientation relation is set to be a near Kurjumov-Sachs relation which is a well-known preferential orientation relation between precipitate and matrix in this system, nucleation of the phase transformation ( ) occurs and the resulting orientation relations become closer to the preferential one. These facts mean that the critical condition for the occurrence of the "nucleation" may be attributable to the interfacial erergy criterion on the ( / )-interphase boundary and the grain-boundary between the _o - and _n - phases.Study to reveal the relationship between structures and sliding behavior of the interphase boundary in two-phase ( / ) stainless steel bicrystals are in progress.