EFFECTS OF MICROSTRUCTURE AND TEST METHOD ON FRACTURE TOUGHNESS OF Mn-Zn FERRITE.

Both hot-pressed polycrystalline specimens with different grain sizes and single crystal of Mn-Zn ferrite were employed as experimental materials. The fracture toughness (K//I//C) of Mn-Zn ferrite was measured using indentation method (IM), straight-through notched beam (STN) and chevron notched beam (CHN). An intrinsic K//I//C value of Mn-Zn ferrite was obtained from STN specimen with sharpening crack tip of radius 20 mu m. K//I//C (IM) decreased with increasing grain size, whereas K//I//C (CHN) increased with increasing grain size. The different results of IM and CHN evaluation of the polycrystalline Mn-Zn ferrite with varied grain sizes are considered to be related to micro-effect of grain-boundary and R-curve behavior of microcrack process zone, respectively. The toughness anisotropy of single crystal of Mn-Zn ferrite was also presented and the correlation of K//I//C between single crystal and polycrystalline Mn-Zn ferrite was given.