Effect of Ni Addition on Fatigue Properties of Bulk Glassy Zr₅₀Cu₄₀Al₁₀ Alloys

Abstract

We examined Wöhler curves of Zr₅₀Cu₄₀Al₁₀ and Zr₅₀Cu₃₀Ni₁₀Al₁₀ bulk glassy alloys (BGAs) using a rotating-beam fatigue test to evaluate the effect of addition Ni on fatigue strength. As a result, we found that the fatigue limit was increased from 250 MPa to 500 MPa by adding 10 at% Ni instead of Cu to a Zr₅₀Cu₄₀Al₁₀ BGA. Zr₅₀Cu₄₀Al₁₀ BGAs exhibit wider fatigue-fractured region with striation-like marks than that of Zr₅₀Cu₃₀Ni₁₀Al₁₀ BGAs. Additive Ni element limits the fatigue-fractured region to half of the whole fractured surface. We also measured dimensions of fatigue-fracture area of Zr₅₀Cu₄₀Al₁₀ and Zr₅₀Cu₃₀Ni₁₀Al₁₀ BGAs to estimate the value of fatigue-fracture toughness. Especially, the fatigue fracture toughness decreases suddenly around 10³ ∼ 10⁴ cycles, similar to the Wöhler curves. The significant decrease of fatigue-fracture toughness originates from embrittlement/hardening in front of the fatigue crack tip during fatigue test.