PRODUCTION OF NANOSTRUCTURAL NT SHAPE MEMORY COMPOUND VLAMECHANCAL. ALLOYNG PROCESS

Due to unique shape memory and superellasticity behavior, NiTi shape memory compound has attracted attentions in many applications such as medical, automotive and aerospace industries. In this research, nanocrystalline NiTi powder (with equal atomic percentage) has been produced by mechanical alloying (MA) method. MA process was chosen because of Cost saving, ease of use and creating nano-structured compositions. High purity initial elemental powders were mixed with employing stearic acid as the process control agent (PCA) under argon atmosphere in a hardened steel container. The effect of milling time on the grain size and microstrain of samples was studied. The grain size and microstrain was calculated by XRD patterns and Williamson-Hall formula. The X-ray diffraction (XRD) analysis indicated that formation of intermettalic NiТi with crystalite size of 22 nm after 60 h of ball milling. In order to investigate the morphology of powders at various MA times, the microstructure of fabricated samples was studied with scanning electron microscopy (SEM) and illustrated homogeneous distribution of formed phases with globular-structure.Annealing of as-milled powders at 1173 K for 900s leads to formation of nanometric NiTi (B19 ), TiNi and NisTiphases.

Keywords:

Mechanical Alloying , Nanostructural , NiТi , Shape Memory