Control of Mechanical Properties of Three-Dimensional Ti-6Al-4V Products Fabricated by Electron Beam Melting with Unidirectional Elongated Pores

Aligned, unidirectional, elongated pores were incorporated in Ti-6Al-4V products fabricated by electron beam melting in order to control the mechanical properties of the products such that they became suitable for biomedical applications. Unidirectional pores were successfully produced when the scan spacing of the electron beam was greater than the diameter of the beam. By changing the scan spacing of the electron beam, the size of the unidirectional pores could be varied. As a result, both the Young's moduli and the yield stresses of the products with unidirectional pores decreased linearly with an increase in their porosity, owing to the stress concentration coefficient being 1 in the equation representing the relation between strength and porosity for porous materials. Further, low (< 35 GPa) Young's moduli were obtained when the scan spacing was 1 mm or higher, with these values being were close to the typical Young's modulus of human cortical bone. This suggested that these porous materials could be used to fabricate customized bone implants that exhibited desired mechanical properties and suppressed the stress shielding of bone that is normally noticed when implants made of Ti alloys are used.