Temperature dependence of fracture toughness in a micro-sized Ni-P amorphous alloy

Temperature dependence of fracture toughness has been studied on micro-sized Ni-P amorphous alloy specimens. The material used in this study was a Ni-11.5wt%P amorphous thin film. The specimens were prepared in a cantilever beam type configuration of dimensions of 10×12×50 μm by focused ion beam machining. Fatigue pre-cracks were introduced into all the specimens. Temperature was controlled using a newly developed specimen holder from room temperature to 473 K. Compared with room temperature, fracture toughness was increased approximately 36 % at 373 K but decreased 16 % at 473 K. From the transmission electron microscope (TEM) observation, no precipitation of crystalline phase was observed in plastically deformed regions tested at 373 K. Differential scanning calorimetry (DSC) measurement also revealed that no crystallization occurred at a temperature range from 300 to 473 K. From these results it is considered that fracture toughness of an amorphous alloy may be changed due to short or medium range order structural relaxation caused by heating.