| Summary: | 碩士 === 南臺科技大學 === 機械工程系 === 104 === In the present study, the molecular dynamics investigations on physical characteristics of solid and hollow spherical titanium and tantalum nanoparticles during laser powder bed fusion additive manufacturing (3D Printing) process are exhibited under different sizes and heating rates. As for titanium, the sizes of titanium nanoparticles are varied from 16a, 20a and 24a, respectively. In addition, the sizes of tantalum nanoparticles are varied from 10a, 16a and 24a, respectively. Regarding both titanium and tantalum, the six combinations of both spherical solid and hollow two-nanoparticle-model are chosen, respectively. The bond angle, neck width, potential energy and gyration radius are utilized to realize the physical properties of nanoscale metallic powders under laser sintering process.
Whatever solid or hollow titanium and tantalum nanoparticles, the present results show that the solid state sintering automatically takes place at room temperature. The temperatures of phase change, coalescence, melting of titanium nanoparticle decreased with particle diameter decreasing, but increased with heating rate increasing. Moreover, the temperatures of phase change, coalescence, melting of hollow spherical titanium nanoparticle are also lower than those of solid ones. Meanwhile, we also found that the temperatures of coalescence and melting of tantalum nanoparticle decreased with particle diameter decreasing, but increased with heating rate increasing. At the same time, the temperatures of coalescence and melting of nanoscale hollow tantalum nanoparticle are lower than those of solid ones, also.
It is found that the phase change temperature (1220K-1325K) of nanoscale titanium is a little higher than that of bulk titanium, 1155K. Nevertheless, the melting temperature (1200K-1350) of nanoscale titanium is much lower than the melting point of bulk titanium, 1940K. At the same time, it is also found that the melting temperature (2400K-3000K) of nanoscale tantalum is much lower than the melting point of bulk tantalum, 3290K.
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