Fatigue crack growth of Fe81B13.5Si3.5C2 amorphous metal using magnetostrictive behaviour to generate ΔK

Abstract

The fatigue crack growth behaviour of Fe81B13.5Si3.5C2 amorphous metal (Metglas 2605SC) was examined. An experimental apparatus was developed to generate the applied stress intensity range, ΔK using the magnetostrictive behaviour of the material. Cycles of elastic strain were accumulated at the natural frequency of the specimens (44 or 56 kHz) with the crack length being monitored optically at certain cycle increments. Through-the-thickness, centre-cracked panel specimens were tested in the as-cast and annealed conditions. Annealing temperatures were 250 and 450 °C. Several specimens annealed at 300 °C, while being subjected to a transverse magnetic field, were also tested. Examination of the fatigue crack growth rate data indicated no differences between the as-cast and the annealed only specimens. The specimens that were annealed while being subjected to the transverse magnetic field, however, exhibited much greater resistance to fatigue crack growth. Microscopy using a Kerr-effect magneto-optical microscope revealed that the magnetic domain boundaries within the material exerted a significant influence on the direction of the fatigue crack propagation and the overall crack growth rate behaviour.