加工熱処理された工業用純チタン調和組織材料の微小疲労き裂発生および伝ぱ特性

抄録

Commercially pure (CP) titanium with a bimodal harmonic structure, which is defined as coarse grained regions surrounded by a network of fine grains, was fabricated by consolidating mechanically milled powders to improve both strength and ductility. In this study, thermo-mechanical processing was performed for the CP titanium with a bimodal harmonic structure to improve the fatigue properties. In order to determine the fatigue properties of thermo-mechanical processed CP titanium with harmonic structure, four-point bending fatigue tests were conducted at a stress ratio of 0.1 under ambient environment. The fracture surfaces and the specimen surfaces were analyzed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) to identify the mechanisms of small fatigue crack initiation and propagation on the basis of fractography and crystallography. Thermo-mechanical processed CP titanium with harmonic structure had longer fatigue life than CP titanium with harmonic structure. This was attributed to the increase of the fatigue crack initiation resistance. On the other hand, the small crack growth rate behavior in thermo-mechanical processed CP titanium was almost the same as CP titanium with harmonic structure. Consequently, the small fatigue crack initiation and propagation properties of thermo-mechanical processed CP titanium with harmonic structure were clarified.