Mechanical properties for bulk metallic glass with crystallites precipitation and second ductile phase addition

Monolithic phase bulk metallic glasses (BMGs) produced by a copper mold casting method and BMG composites containing in-situ brittle crystallites and out-situ tungsten fiber produced by a water quenching method were obtained. Mechanical properties including cyclic deformation and fracture toughness were investigated. Under symmetrically cyclic stress control, the life of tungsten fiber reinforced amorphous alloy is much longer than that of the monolithic amorphous alloy. The composite containing tungsten fibers that retard the crack propagation exhibits cyclic softening while the partially crystallized amorphous alloy exhibits stable cycling. The regions of crack initiation, stable propagation and final fracture were observed on the fracture surface. Crystalline brittle phases do not retard the crack propagation but become sites of crack initiation. Tungsten fiber reinforced BMG has the largest fracture toughness while BMG with quenched-in crystallites the smallest. Tungsten fibers stabilize crack growth in the matrix and extend the strain to failure of the composite, while brittle crystallites speed up the crack propagation even though they act as obstacles when shear bands reach them in some cases.