銅単結晶の疲労破面近傍における格子回転のEBSD解析

抄録

Lattice rotation near a fracture surface of fatigued copper single crystals was investigated by EBSD analysis. Two copper single crystals having [372] and [010] longitudinal axes were grown by the Bridgman method. The single crystals were shaped to a plate shape of 50×20×3 mm³ dimension. The single crystal plates were preliminarily hardened by cyclic loading and then a small notch was introduced at each center of the single crystal plates. Fatigue crack growth tests were carried out on the notched samples. After the surface was polished again, lattice rotation near a fracture surface was analyzed by EBSD system. In the single-slip-oriented single crystal having the [372] tensile axis, a primary fatigue crack was grown almost along (111) primary slip plane in a shear decohesion manner. Near the notch root at which the stress intensity factor is low, there existed almost no lattice rotation even in the close vicinity of the fracture surface. However, at a long crack length near which slip bands of secondary system were visible on a surface, lattice rotation was clearly detected. The maximum lattice rotation angle at an intermediate crack length was about 20°. In the multiple-slip-oriented single crystal having the [010] tensile axis, the crack growth direction was basically towards the notch direction. At a longer crack, the maximum lattice rotation angle amounted to about 30°, which exceeded the maximum angle at the [372] single crystal. However, the surface area where lattice rotation is detectable was small at the [010] single crystal than that at the [372] single crystal at an equal crack length.