腐食ピットを有するZr基バルク金属ガラスの疲労き裂発生に関する研究

抄録

Zr₅₅Cu₃₀Ni₃₀Al₁₀ bulk metallic glass (BMG) is expected to be applied in a wide range of fields due to its high strength and high corrosion resistance. In this study, 4-point bending fatigue tests have been conducted in air and in distilled water to investigate the conditions of corrosion fatigue crack initiation focusing on the behavior of corrosion pits formed during fatigue tests. The fracture surface and the tensile surface were observed using a laser microscope and a scanning electron microscope (SEM). Experimental results show a decrease of fatigue strength in distilled water compared with air. It is considered that fatigue cracks initiated earlier than in air due to stress concentration at corrosion pits. In addition, the stress intensity factor range at the crack initiation ΔK_ci was calculated from the fractured surface observation using √area method. ΔK_ci fell within the range of 2.3 ~ 3.6 MPa√m for low stress level range tests. However, since ΔK_ci increases with increasing stress, it is suggested that ΔK_ci has stress dependency. Finally, the aspect ratio α of the corrosion pit, where the fatigue crack initiated, was about 1.4 regardless of the stress level. It suggests that it is necessary to consider the shape of the corrosion pit in fatigue crack initiation condition.