IN SITU NEUTRON DIFFRACTION OF ADDITIVE MANUFACTURED Ti6Al4V UNDER TENSILE STRESS

Yaron Ganor ^1,4 Maria Strantza ² Bjorn Clausen ² Donald Brown ² Roni Z. Shneck ¹ Eitan Tiferet ^3,4 Ori Yeheskel ³

¹Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel
²Los Alamos Neutron Science Center, Los Alamos National Laboratory, Los Alamos, New Mexico, USA
³Department of Materials Science, Nuclear Research Center Negev, Beer-Sheva, Israel
⁴Additive Manufacturing Center, Rotem Industries, Rotem Industrial Park, Israel

Additive Manufacturing (AM) of Ti6Al4V alloy specimen by Electron Beam Melting (EBM) results in a unique microstructure characterized by micron and sub-micron sized grains with an orientation that is particular to the AM process. The phase content of the specimen is composed primarily of α phase with trace β phase. As part of ongoing research pertaining to the mechanical properties of AM Ti6Al4V, specimens were subjected to neutron diffraction in the SMARTS facility in the Los Alamos Neutron Science Center. The in-situ measurements of tension samples of AM Ti6Al4V that underwent different thermal treatments showed that AM Ti6Al4V samples are not prone to hysteresis. Specimens were loaded until certain stress and then unloaded, while measurements took place at normal intervals during loading and unloading in the elastic region. After reaching yield stress, specimens underwent strain to 1%, 4%, and 10% strain with in-situ measurements during loading and unloading. No hysteresis was measured during elastic or plastic deformation. The proposed explanation to the apparent lack of hysteresis lies with the unique microstructure of AM Ti6Al4V. The extremely small grain sizes in AM Ti6Al4V do not have enough bulk to allow for dislocation movement or dislocation hardening mechanisms. One of the specimens underwent a thermal treatment that generated a more substantial β phase content and larger grains, however hysteresis was not measured in the said specimen as well.