Ural Federal University named after B. N. Eltsin, Ekaterinburg, Russia:
Yu. N. Loginov, Professor of the department of metal forming, e-mail: j.n.loginov@urfu.ru
S. I. Stepanov, Associate professor of the department of heat treatment and physics of metals

JSC “NPO TSNIITMASH”, Moscow, Russia:
A. V. Yudin, Senior scientific employee
E. V. Tretyakov, Deputy Director of the Institute of surface technology and nanomaterials for planning and production work

The purpose of the study was to establish the relationship between the relative density and the mechanical properties of commercially pure (CP) Ti samples manufactured using additive technology. The Ti powder of spherical shape and the particle size in a range of 10–50 μm was utilized as a raw material for 3D printing. Chemical composition was determined on ARL 9900 Workstation by means of X-ray fluorescent spectrometry (mass.%): 99,8 Ti; 0,07 Ce; 0,04 Nd; 0,04 Fe; 0,03 Mg; 0,02 Pr; 0,01 Cr; 0,002–0,005 Mn, Ni, P, Si. Oxygen content of 0.10 mass.% was found employing Leko TS-136. The comparison of the chemical composition of the powder revealed that it had a low content of the impurities, which is an important parameter for achieving the required properties in manufacturing of high quality implants. Samples for studying the physical and mechanical properties of the material were fabricated in a device of layer-by-layer synthesis using selective laser melting (SLM) technique. The following operating parameters of the apparatus were chosen: the size of the laser spot of about 60–70 μm, the powder layer thickness of 50 μm, argon shielding atmosphere (oxygen content less than 900 ppm). Bone-shape specimens for tensile test were machined from the cylindrical work-piece so that building direction during SLM was perpendicular to specimen axis. Then specimens were tested to fracture. The density of the material was estimated by hydrostatic weighing. Microstructure was examined using the light optical microscope OLYMPUS GX-51 and scanning electron microscope JEOL JSM-6490 LV. The samples obtained were characterized by alternating density due to the variation of operating parameters in the above ranges. Each density was characterized by the definite mechanical properties. The linear correlation of yield stress (YS), elongation and relative density were obtained. For relative density of 92%, the yield stress was equal to 300 MPa, and for the higher densities, YS exceeded the values of 500 MPa. Applying of additive manufacturing for CP Ti provided a residual porosity characterized by a relative density in a range of 92–99%. The as-received material has improved strength compared to CP Ti with the same purity of chemical composition produced by traditional methods despite the presence of pores. Both yield strength and elongation to fracture demonstrate direct-proportionality with the relative density, i.e. improvement of both strength and ductility characteristics took place. The reduced density was due to the presence of pores formed during laser melting of particles having limited surface contact between them.
This work was carried out with the financial support of the governmental order of the Russian Federation No. 218 on 09.04.2010, agreement No. 03.G25.31.0234.

1. Sercombe T. B., Xu X., Challis V. J., Green R., Yue S., Zhang Z., Lee P. D. Failure modes in high strength and stiffness to weight scaffolds produced by Selective Laser Melting. Materials and Design. 2015. Vol. 67. pp. 501–508.
2. Yong-Keun Ahn, Hyung-Giun Kim, Hyung-Ki Park, Gun-Hee Kim, Kyung-Hwan Jung, Chang-Woo Lee, Won-Yong Kim, Sung-Hwan Lim, Byoung-Soo Lee. Mechanical and microstructural characteristics of commercial purity titanium implants fabricated by electron-beam additive manufacturing. Materials Letters. 2017. Vol. 187. pp. 64–67.
3. Moiduddin K., Al-Ahmari A., Al Kindi M., Nasr E. S., Mohammad A., Ramalingam S. Customized porous implants by additive manufacturing for zygomatic reconstruction. Biocybernetics and Biomedical Engineering. 2016. Vol. 36. pp. 719–730.
4. Srimanta B., Subhomoy Ch., Sourav M., Alok K., Bikramjit B. Microstructure and compression properties of 3D powder printed Ti – 6Al – 4V scaffolds with designed porosity: Experimental and computational analysis. Materials Science and Engineering: C. 2017. Vol. 70. pp. 812–823.
5. Yuzhakova E. A., Kotlyarov V. I., Beshkarev V. T., Ivanov V. V. Obtaining of polygonal powder of titanium and its alloys with given granulometric composition for additive technologies. Tsvetnye Metally. 2016. No. 12. pp. 63-68. DOI: 10.17580/tsm.2016.12.10
6. Mühlich U., Zybell L., Kuna M. Micromechanical modelling of size effects in failure of porous elastic solids using first order plane strain gradient elasticity. Computational Materials Science. 2009. Vol. 46, No. 3. pp. 647–653.
7. Salvatore F. On the linear elasticity of porous materials. International Journal of Mechanical Sciences. 2010. Vol. 52, No. 2. pp. 175–182.
8. Loginov Yu. N., Popov A. A., Stepanov S. I., Kovalev E. Yu. Test for the draft of a porous implant obtained by the additive method from a titanium alloy. Titan. 2017. No. 2. pp. 16–20.
9. Titanium Grade 1, Annealed. Online Materials Information Resource — MatWeb. Available at: http://www.matweb.com/search/DataSheet.aspx?MatGUID=d3e4887d426a47ea9b82fdcb155a3faf
10. Titanium Grade 2, Annealed. Online Materials Information Resource — MatWeb. Available at: http://www.matweb.com/search/DataSheet.aspx?MatGUID=49a4b764217b44ee953205822af5fbc9
11. Titanium Grade 3, Annealed. Online Materials Information Resource — MatWeb. Available at: http://www.matweb.com/search/DataSheet.aspx?M atGUID=09ee8cd4391e4048bd25d62285b11c6b
12. Titanium Grade 4, Annealed. Online Materials Information Resource — MatWeb. Available at: http://www.matweb.com/search/DataSheet.aspx?MatGUID=f1570881ceb44ef6b1c345c03909021d
13. GOST 15139–69. Plastics. Methods for determining the density (bulk mass). Introduced: 1970–07–01.
14. ISO 5832-2:1999. Implants for surgery — Metallic materials — Part 2: Unalloyed titanium.
15. Loginov Yu. N., Sharafutdinov N. N., Kolmogorov V. L. On the equations of stress-strain relation for a compressible rigid-plastic material. Tekhnologiya legkikh splavov. 1977. No. 4. pp. 20–25.
16. Galarraga H., Lados D. A., Dehoff R. R., Kirka M. M., Nandwana P. Effects of the microstructure and porosity on properties of Ti – 6Al – 4V ELI alloy fabricated by electron beam melting (EBM). Additive Manu facturing. 2016. Vol. 10. pp. 47–57.
17. Potapov A. I., Loginov Yu. N., Vichuzhanin D. I. Effect of density on the resistance of deformation of sponge titanium. Zagotovitelnye proizvodstva v mashinostroenii. 2010. No. 4. pp. 24–27.
18. Basalah A., Esmaeili S., Toyserkani E. On the influence of sintering protocols and layer thickness on the physical and mechanical properties of additive manufactured titanium porous bio-structures. Journal of Materials Processing Technology. 2016. Vol. 238. pp. 341–351.
19. Thijs L., Verhaeghe F., Craeghs T., Van Humbeeck J., Kruth J.-P. A study of the microstructural evolution during selective laser melting of Ti – 6Al – 4V. Acta Materialia. 2010. Vol. 58. pp. 3303–3312.
20. Han G., Muller W. E. G., Wang X., Lilja L., Shen Z. Porous titania surfaces on titanium with hierarchical macro- and mesoporosities for enhancing cell adhesion, proliferation and mineralization. Materials Science and Engineering: C. 2015. Vol. 47. pp. 376–383.