High temperature synthesis of single-phase Ti3Al intermetallic compound in mechanically activated powder mixture

The influence of the duration of preliminary mechanical activation on the microstructure of the powder mixture of 3Ti + Al and the features of the kinetics of the thermal explosion processes in milled powder mixtures were studied. It was shown that the formation of highly defective crystalline structures with high curvature of the lattice and high internal stress gradients took place with the increase of milling time. It was found that the features of heating during the thermal explosion process were determined by the features of the microstructure of the milled mixture. As a consequence, the composition of the product depended on the milling time and also on the heating rate of the mixture by the external heating source. Thus, the milling time and the heating rate can be considered as the control parameters in the research.The reacting system turned into the stable mode of phase formation characterized by the formation of mechanocomposites with the increase of milling time. The process was accompanied by the decrease in the effective activation energy of the synthesis down to the anomalous low value. The modes of the synthesis realization were determined to obtain a strictly single phase compound Ti3Al. It was hypothesized on the transition of the process from the diffusion regime of phase formation to the kinetic one with milling time.

With an increase of the time of preliminary mechanical activation, the transition to a stable regime of phase formation in the thermal explosion mode occurs. After 5 min of milling time (300 J/g), the reaction takes place in one stage.Figure optionsDownload as PowerPoint slideHighlights
► After mechanical milling, components Ti and Al have a high lattice curvature.
► High heating rate promotes formation of single-phase compound Ti3Al.
► Prolonged preliminary activation promotes formation of Ti3Al during the heating.
► With an increase of milling time the activation energy of reaction decreases.