Fe 65.5Cr 4Mo 4Ga 4P 12C 5B 5.5 BMGs: Sample preparation, thermal stability and mechanical properties

Abstract

Bulk amorphous Fe-based alloys with the nominal composition Fe 65.5Cr 4Mo 4Ga 4P 12C 5B 5.5 have been obtained by copper mold casting in different shapes: cylindrical rods with diameters up to 3 mm, rectangular bars of 2 mm × 2 mm and discs of 10 mm diameter and 1 mm thickness. These alloys exhibit good soft magnetic properties, characterized by low coercivity and high saturation magnetization. Besides the magnetic properties, the Fe 65.5Cr 4Mo 4Ga 4P 12C 5B 5.5 bulk metallic glass (BMG) shows a high glass transition temperature T g, as well as a high crystallization temperature T x, with an extension of the supercooled liquid region of around 65 K. The mechanical behavior was investigated by compression and Vickers hardness tests. The fracture strength for the as-cast samples σ f is 2.8 GPa and the fracture strain ɛ f is 1.9%. Upon annealing at 715 K for 10 min, i.e. at a temperature below the calorimetric glass transition, the fracture strain drops to 1.6% and no plastic deformation is observed. The Vickers hardness H V for the as-cast samples is about 885, and increases to 902 upon annealing. The fracture behavior of these Fe-based bulk glassy alloys is significantly different in comparison with the well-studied Zr-, Cu- or Ti-based good glass-formers. The fracture is not propagating along a well-defined direction and the fractured surface looks irregular. Instead of veins, the glassy alloy develops a high number of microcracks.