Effects of Sample Size on the Fracture Behavior in Fe-3%Si Alloy Single Crystals

Abstract

Fracture tests have been performed for both macro-and micro-sized specimens prepared from an Fe-3%Si alloy single crystal, and the effects of specimen size on fracture behavior have been investigated. Micro-sized cantilever beam specimens with dimensions of 10 x 10 x 50 µm 3 were prepared by focused ion beam machining. Notches with a depth of 5 µm were introduced into the micro-sized specimens and fatigue pre-crack was also introduced ahead of the notch. Macro-sized three-point bending specimens with dimensions of 2 x 2 x 10 mm 3 were also cut from the same Fe-3%Si alloy single crystal. Notches with a depth of 1mm were introduced into the macro-sized specimens, and fatigue pre-crack was also introduced. The notch plane was set to be (100), which is a cleavage plane of this material, and the notch direction was set to be [010] for both size of specimens. For macro-sized specimens, cleavage fracture occurred during introducing fatigue pre-crack. In contrast, the micro-sized specimens were fractured by ductile manner. A plastic zone was clearly observed on the specimen surface near the crack tip and dimples were found on the fracture surface. The plastic zone size of this material is calculated to be 90 µm. This size is small enough to satisfy small scale yielding for macro-sized specimens, although this size corresponds to large scale yielding in micro-sized specimens. This may cause the size effect on the fracture behavior of this material.