Constitutive behavior and microstructural evolution in Ti–Al–Si ternary alloys processed by mechanical milling and spark plasma sintering

Abstract

Severe plastic deformation is closely related to the microstructural behaviors of intermetallics or grain refinement by mechanical milling and subsequent rapid sintering process, i.e. high energy ball milling and spark plasma sintering. In this study, the Ti–Al–Si ternary powders were synthesized to investigate their phase transformation by plastic deformation during the mechanical milling in each process time and composition. The sintered-bodies Ti–Al–Si ternary alloys were fabricated by spark plasma sintering among the rapidly consolidated powders, except for the distribution of single phases in accordance with the Al-melting. The microstructures of intermetallics in Ti–Al–Si ternary alloys were composed of titanium aluminides and titanium silicides, and even ternary compounds as a τ1-phase. In particular, the twining or stacking faults induced by severe plastic deformation were revealed through crystallographic patterns and microstructural evidence. These defects were caused by the slip system for TiAl3 (fcc) or Ti5Si3 (hcp) phases, depending on the grain refinement and generation of ambient intermetallics. To estimate the possibility of these defects, various approaches were taken to obtain experimental measurement of the twin probability and stacking fault energy derived from TEM and XRD analyses. Keywords: Ti–Al–Si, Mechanical alloying, Spark plasma sintering, Intermetallics, Severe plastic deformation