Crystallographic features of α variants and β phase for Ti-6Al-4V alloy fabricated by selective laser melting
School of Engineering
The present study investigated the crystallographic features of α variants and β phase for Ti-6Al-4V alloy fabricated by selective laser melting. The <100>β fiber texture parallel to the building direction was ascertained on the basis of a reconstruction method realized by the manipulation of stereographic projection. The SLMed alloy has no α/α′ variants selection but contains a special crystallographic area exhibiting random orientation which cannot be reconstructed as a parental columnar β grain with the present introduced method due to its nature as the overlapped area between adjacent melt pools resulting from the heterogeneous nucleation in front of the liquid-solid interface. With increasing the heat treated temperature, α variants selection occurs. Especially at higher temperature of 905 °C, the intergranular β phase following a reversed crystallographic path as “parental β phase”→“α variants”→“intergranular β phase” would be precipitated, therefore the intergranular β phase keeps the same orientation with the parental β phase. Once the alloy was heat treated at 975 °C close to Tβ, the microstructure is characterized by primary α variants selection and a large amount of secondary α widmanstatten structure with a homogeneous orientation which accounts for the lowest tensile strength. The decomposition of twelve α variants proved the BOR <110>β//(0001)α, <111>β//<2-1-10>α. The misorientation between two variants sharing a common parental <100>β pole with a similar color consisting of all Euler angles was identified to be  α/10.53°.