Properties of Ti-Ni Pre-alloyed Powder Used for Electron Beam Melting

The properties of pre-alloyed powder have an important influence on the additive manufacturing process, especially for Ti-Ni alloys with special shape memory effects. However, there are limited reports on the studies for the variation of Ti-Ni pre-alloyed powder with heat treatment temperatures and number of thermal cycles. In this work, the phase transformation behavior, microstructure and phase composition of 53 similar to 106 mu m Ti-Ni pre-alloyed powder used for electron beam melting (EBM) were studied using the differential scanning calorimeter, X-ray diffraction, and scanning electron microscope. The results show that the powder has good particle size distribution, internal filling and spherical topography, and suitable for EBM process. The structure and composition become uniform, internal stress and dislocation are eliminated and crystal grain size grows with the increase of heat treatment temperature, which causes the original multi-step phase transformation to one-step phase transformation during the heating and cooling process after 550 degrees C and the phase transformation points maintain a stable state after 650 degrees C heat treatment. The phase composition is not changed during the heat treatment process and the powder has best sintering state at 750 degrees C. The phase composition, one-step phase transformation behavior and phase transformation points are all not changed for the powder during 750 degrees C thermal cycles test, indicating good thermal cycling stability. Ti-Ni solid samples with good surface condition are successfully prepared under 750 degrees C preheating temperature for bottom plate and powder layer.