Laser sintering of titanium dioxide and hydroxyapatite bimodal distributed powders - Optimization of distributions powder for selective laser sintering processes

In selective laser sintering (SLS) and selective laser melting (SLM) a laser beam is used to partially (SLS) or completely (SLM) melt particles in a layer of powders [1]. With subsequent increments of powder layers it is possible to create three dimensional structures. This technique can be used in prototyping applications able to produce customized objects of predetermined shape. With SLS it is possible to process not only plastics but also ceramics and metals, therefore it appears to be particularly suited to build three dimensional scaffolds made of biocompatible materials, such as titanium oxide and hydroxyapatite to be used in biomedical applications [2,3]. In SLS techniques increasing the energy transferred by laser increases the strength of the structure obtained, but it also produces a volume contraction of the sintered material which reduces the precision of the final object [4]. Since the energy required for sintering depends on the particle size. The use of smaller particles allows the use of smaller sintering energies and therefore the production of complex and more precise structures due to reduced melting [5] In this paper mixtures of powders with different particle size distributions of biocompatible materials has been obtained by mixing a coarser grained powder, with particles in the range between 10 and 100 microns, and a finer grained powder, with particles in the submicron range. By optimal combination of the powder laying procedure and of the powder mixtures granular distribution it has been possible to obtain scaffold specimens with the two materials. The equipment used is a home-made three dimensional laser sintering equipment using a 40W CO2 laser beam. The density and the mechanical resistance of the specimens are studied as a function of the fines content and of the amount of energy released by the laser beam on the unit surface of the lighted area. A simple model approach is used to estimate the strength of the single sintered contact. References [1] Tang, Y., Fuh, J.Y.H., Loh, H.T., Wong, Y.S., Lu, L. 2003 Direct laser sintering of a silica sand. Materials and Design 24, 623–629 [2] Shishkovskii, I.V., Yadroitsev, I.A. and Smurov I.Y. 2011 Theory and technology of sintering, thermal and chemicothermal treatment: selective laser sintering/melting of nitinol–hydroxyapatite composite for medical applications. Powder Metallurgy and Metal Ceram. 50, 275-283. [3] Shuai, C., Feng, P., Cao, C., Peng, S. 2013 Processing and characterization of laser sintered hydroxyapatite scaffold for tissue engineering. Biotechnol. Bioproc. Eng. 18, 520-527. [4] Tia, X., Günster, J, Melcher, J., Li, D., Heinrich, J.G. 2009 Process parameters analysis of direct laser sintering and post treatment of porcelain components using Taguchi’s method. J. Europ. Ceram. Soc. 29, 1903–1915. [5] Salmoria, G.V., Klauss, P., Modolon Zepon, K., Kanis, L.A. 2013 The effects of laser energy density and particle size in the selective laser sintering of polycaprolactone/progesterone specimens: morphology and drug release. Int. J. Adv. Manuf. Technol. 66, 1113–1118.