3340 ジルコニア基金属ガラスの変形と破壊(S18-5 アモルファス合金,S18 材料の強度と組織)

抄録

Behaviors of fracture and deformation behaviors in a Zr-Al-Ni-Cu bulk metallic glass (BMG) was investigated by using three-point bending tests. Apparent fracture toughness obtained by bending tests was about 40MPam^<1/2> which is comparable to the value of ductile crystalline metals. This high toughness of the BMG should be understood by the cracktip plasticity as well as those of crystalline metals. It is well known that plastic deformation occurs very inhomogeniously when BMGs are deformed at mom temperature. Such inhomogenity is manifested by the appearance of surface steps caused by localized shear deformation. In the present study, TEM observations for shear bands were carried out using foil specimens prepared by FIB technique. In addition, the surface steps due to the localized shear bands near a fracture surface have been examined in detail by using SEM and AFM. The variation of the step height indicates the gradient of plastic shear deformation, and it can be understood, in principle, as the introduction of elastic singularities corresponding dislocations in the case of crystalline materials.