日本金属学会誌

We investigated how dwell fatigue loading accelerates the crack propagation in bi-modal Ti-6Al-4V alloy. A fatigue test was programmed to include displacement holding for only one cycle at several ΔK. We found (1) crack tip strain evolved during the displacement holding, (2) the displacement holding increased fatigue striation spacing, and (3) the strain increment during the displacement holding was linearly correlated with spacing of the displacement-holding-extended striations. These facts indicate that the dwell loading assisted crack opening, which accelerated the crack propagation. Other analyses results and discussion are also presented, in terms of crack propagation mode, crack closure, and dislocation structure.

Mater. Trans. 63 (2022) 1232-1241に掲載

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In this study, SiC (10 vol％) reinforced AlSi10Mg (Al-10 mass％Si-0.35 mass％Mg) alloy matrix composites were fabricated by laser powder bed fusion (L-PBF) process. The effect of laser re-melting scan on densification behavior, microstructural formation and mechanical properties of the specimens was examined. The relative density of the specimens increased by applying re-melting scan, especially under the condition of a low input energy density less than 200 J/mm³. No change was found in eutectic cell size in the microstructure of specimens by laser re-melting. On the other hand, the decomposition of SiC particles with corresponding formation of Al₄SiC₄ phase was enhanced and the hardness of the matrix region (excluding SiC particles) increased. A high ultimate compressive strength of 700 MPa was obtained when the composite was fabricated under an optimum building condition with re-melting scan due to the densification, a high volume fraction of SiC and fine microstructures.

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