SYNTHESIS AND CHARACTERIZATION OF Ti - Mg ALLOYS OBTAINED BY MECHANICAL ALLOYING

Abstract

The very low mutual miscibility between Mg and Ti has led to the search for synthesis methods that incorporate structural elements to increase the solubility between the two elements. Mechanical alloying is a synthesis technique that by fracture and continuous welding incorporates an important density of dislocations to the alloying process. In this work, using high purity powders of Magnesium and Titanium, alloys of Ti 1% and 20% mass Mg (Ti1Mg, Ti20Mg) were synthesised through the mechanical alloying process and subsequently analysed through various analytical techniques. By means of the X-Ray Diffraction technique, the mixtures of the initial powders and their evolution during the grinding were characterized, which allowed us to have access to the crystalline cut. The morphological changes and the particle size of the powder as the milling progressed were observed by Optical Microscopy and Scanning Electron Microscopy with EDS analysis. Exo and endothermic reactions of Ti-Mg powders were studied by Differential Scanning Calorimetry. XRD analysis revealed the formation of a Ti-Mg solid solution and a significant HCP to FCC transition possibly generated by the decomposition of oxygenated TiMg compounds and by the micro-deformations formed during grinding. From the analysis of the micrographies of the alloys at different grinding times, an appreciable variation in the shape of the particles with respect to the initial one was evidenced. This is due to the plastic deformation to which the powders are subjected, decreasing the particle size from 350 to 20nm and 200 to 20nm for the Ti20Mg and Ti1Mg alloys, respectively. The density study revealed a sustained decrease at the beginning of the grinding process, and then a growth until the final consolidation of the alloys, this behaviour is associated to the evolution of the compacted powder morphology. The exothermic transformations obtained around 400º C by DSC are of diffusive character with activation energy of 200kJ/mol, in accordance with the activation energy for oxygen diffusion in TiMg. Our results confirm the formation of a metastable phase of TiMg in both alloys.