Solid solubility and transformation in mechanically alloyed Ti-Mg powders

Mechanical alloying (MA) was examined by ball-milling the powder mixtures of various starling compositions, Ti-10, 20, 30, 40, 50, 60, 70, 80, 95 at%Mg plus 2 mass%NaCl powder. NaCl powder was an excellent anti-sticking agent for MA. The process of MA was mainly followed by X-ray diffraction and TEM methods. Super-saturated quasi-solid solution was formed for the samples up to 60 at%Mg. A single hcp structure was newly created up to 30 at%Mg samples, and over this composition range hcp peaks were present in addition to the diffraction pattern which will lead to bcc like nano-crystallite. In the Mg-rich side, Ti-70 similar to 95 at%MA samples showed the coexistence of hcp phases, Ti-based and Mg-based dilute solid solution. The solubility was estimated from the change of lattice constant. But it was somewhat difficult to detect the alloying effect of MA on Mg and Ti in Ti-95 at%Mg sample. MA samples, Ti-20 and -50 at%Mg, showed the starting of phase separation after one hour annealing at 673 and 473 K, respectively.