Microstructure in a Ni60Pd20P17B3 bulk metallic glass compressively fractured at cryogenic temperature

In order to clarify relationship between plasticity and microstructure for a Ni60Pd20P17B3 bulk metallic glass (BMG) at cryogenic temperature, we investigated the microstructures of both the shear band and fracture surface for the BMG compressively fractured at room temperature (RT) and 77 K (liquid Nitrogen temperature) using transmission electron microscopy (TEM). HRTEM images from the BMG fractured at 77 K clearly reveal that there are nanocrystalline particles around both shear band and fracture surface, but not in undeformed region. The sizes of the particles fractured at 77 K are smaller than those fractured at RT. These particles ranged from 3 to 5 nm in size are thought to consist of an fcc palladium–nickel solid solution phase. The particles with smaller size and the ductile fcc phase may effectively restrain the propagation of shear bands, resulting in enhancement of plastic deformation at cryogenic temperature.

Research highlights▶ HRTEM images reveal there are nanocrystalline particles near shear band at 77 K. ▶ This is the first direct evidence of deformation-induced crystallites at 77 K. ▶ The sizes of the particles formed at 77 K are smaller than those at RT. ▶ The particles are thought to consist of a ductile fcc Pd–Ni solid solution phase. ▶ They restrain propagation of shear bands, resulting in enhancement of plasticity.