Research On Anisotropy Of Ti6Al4V Alloy Fabricated By Selective Laser Melting

As one of the powder bed-based additive manufacturing technologies, selective laser melting(SLM) has been developed as a new approach to fabricate complex-shaped Ti6Al4V parts recently. However, the directional solidification during SLM of Ti6Al4V alloy makes grains grow along preferential crystallographic orientation to form texture and thus influences its applications due to anisotropic mechanical properties. Until now, the relationships between SLM processing parameters and crystallographic texture as well as the anisotropy of SLMed Ti6Al4V alloy are still lacking.In order to explore the anisotropy of the SLMed Ti6Al4V alloy, the microstructure and crystallographic orientation of Ti6Al4V samples deposited at various laser energy densities and building directions were observed. Also, the anisotropy of tensile properties and microhardness of the samples was measured to investigate the dependence on the microstructure and crystallographic texture. Finally, a method to control the anisotropy of mechanical properties of SLMed Ti6Al4V was obtained by adjusting SLM processing parameters.Results show that laser energy density and building direction play significant roles in deterimining the microstructure, crystallographic texture and anisotropy of SLMed Ti6Al4V. The microstructure of SLMed Ti6Al4V samples consists of acicular ?? martensites with weak texture within prior columnar grains. As laser energy density increases from 80 J/mm3 to 250 J/mm3, the width of columnar grain increases while the width of martensite decreases. Also, the crystallographic orientation of ?? martensites transforms from basal texture of {0001}<11 00> to cone texture of {112 1}<13 23> and {224 1}<12 13>, and eventually transforms to cylindrical texture of {112 0}<11 02> with increasing laser energy density, which results in a more pronounced anisotropy in tensile properties and microhardness. Compared with 90 deg building direction, the finer columnar grains, weaker cylindrical texture and reduced anisotropy of tensile properties and microhardness are obtained when the sample is deposited along 45 deg building direction. A criterion of anisotropy on SLMed Ti6Al4V alloy was proposed by reference to the forging technology. Finally, anisotropy in microhardness, tensile strength, yield strength and elongation of SLMed Ti6Al4V is controlled to be 2.7%, 8.1%, 8.9%, 7.5% respectively by adjusting laser energy density, building direction and scanning strategy, which means that the adjused mechanical properties of SLMed Ti6Al4V are basical isotropous.