Papers by Author: Naoko Sato

Abstract: Spherical powders via gas atomization etc. are recommended for use in SLM, however, the spherical powders are expensive and able to make in limited types of metal materials. Using non-spherical powder in SLM are capable of applying SLM to cheap part production and diversify powder materials for SLM. In this paper, to study the feasibility of using Ti6Al4V milled powder via hydride-dehydride method for SLM, characteristics of powders, powder bed performances, and SLM fabricated samples made from gas atomization powder and milled powder were analyzed and compared. The milled powder which added a fumed silica as a lubricant were also analyzed. In the results, flow and packing characteristics of the milled powder are lower than the gas atomized one. The characteristics of the milled powder are improved by adding fumed silica as lubricant, and had comparable characteristics to the gas atomized one. Microstructure of the SLM fabricated samples has a comparable size and morphology regardless of powders. Hardness of the SLM fabricated sample made from milled powder are larger than that of it made from gas atomized powder, owing to solid solution hardening by oxygen.

Abstract: The features present in 3D structure have geometric properties that fall into two broad categories: topological and metric. Metric properties are generally the more familiar; these include volume, surface area, line length and curvature. Equally or even more important in some applications are the topological properties of features. The two principal topological properties are number per unit volume and connectivity. In the present study, a change in morphology of pearlite and dual phase microstructures was examined from differential geometry and topology viewpoint. 3D images of eutectoid pearlite and dual phase steels were obtained by reconstructing serial sectioning images. Their metric and topological features were evaluated using The Euler Poincare formula and The Gauss-Bonnet Theorem. In addition, newly developed fully-automated serial sectioning 3D microscope “Genus_3D” will be also introduced.

Abstract: Martensite morphology such as connectivity or dispersivity in ferrite (F)/martensite (M) dual-phase (DP) steels was investigated from topological viewpoint to reveal the effect of the martensite morphology on the mechanical properties. Topological analysis permits evaluation of the microstructural connectivity and dispersivity by measuring the number of handles, independent bodies and genus, etc. The topological analysis was performed on three-dimensional (3D) reconstructed images of the microstructure with different connectivity, dispersivity, volume fraction and hardness of martensite in DP steels that were prepared by changing the intercritical annealing temperature. The connectivity and the volume fraction of martensite increased while the dispersivity and hardness of it decreased with increasing annealing temperature. The effect of connectivity and dispersivity as well as volume fraction and hardness, in particular, on work hardening behavior was individually evaluated at a given strain.