Cu-10 mass%Zn合金の高温粒界破壊と粒界性格

抄録

Void formation on grain boundaries in Cu-9.7 mass%Zn alloy has been investigated in connection with the grain boundary character. The alloy was prepared by melting electrolytic copper and pure zinc (99.9%) in high purity argon gas atmosphere. The ingot was hot rolled at 1093 K and then cold rolled to 1 mm in thickness. Tensile tests were performed on an Instron type testing machine in argon gas atmosphere. The initial strain rates were 3.5×10⁻³, 3.5×10⁻⁴ and 3.5×10⁻⁵ s⁻¹. Microstructure and fracture surfaces of the specimens were observed with an optical microscope and a scanning electron microscope. Grain boundaries were characterized from their boundary misorientations by analysing ECPs (Electron Channeling Patterns) taken from two grains.
A ductility minimum appeared at 673 K at any strain rate and the elongation to fracture decreased with decreasing strain rate. The observed ductility loss is attributed to the initiation, growth and coalescence of voids on grain boundaries during deformation. This void formation occurred at smaller strain with increasing test temperature. The minimum sigma value of the cavitated coincidence boundaries was 31 when deformed at 673 K and the initial strain rate of 3.5×10⁻³ s⁻¹. Meanwhile, the sigma value was small as 9 at the initial strain rate of 3.5×10⁻⁴ s⁻¹. Therefore, it was suggested that the strain rate affected the relationship between the propensity to void formation and the grain boundary character.