Nanostructured titanium aluminides prepared by mechanical alloying and subsequent thermal treatment

Ternary Ti–Al–Nb elemental powder blends with minor addition of SiC were synthesized in a high energy ball mill in order to understand the structural evolution during mechanical alloying (MA) and subsequent thermal treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) techniques were employed to study the structural development during MA. Ti–48%Al–4%Nb–3%SiC and Ti–48%Al–8%Nb–3%SiC blends milled to 20 h were subjected to thermal treatment at 750 °C for 1 h in vacuum. Repeated cold welding and fracturing events of MA resulted in nanocrystalline structure with supersaturated solid solution and amorphous phase. The powder particles were also refined to submicron size due to high energy collision. The nanocrystalline supersaturated solid solution evolved by MA was sustained for prolonged milling time. There was no evidence of intermetallics formation even after early solid solubility extension and formation of nanocrystalline structure. However, nanostructured TiAl and Ti3Al intermetallic compounds were observed after giving thermal treatment to MA powder blend. Since their surface area and energy were enhanced to a great extent, the dispersed ceramic particles reacted with titanium and formed nanosilicide particles.

Graphical AbstractMechanically alloyed Ti–Al–Nb–SiC powders exhibited phase transformation with increasing milling time. The initial powder blend transformed into supersaturated solid solution with nanocrystalline structure. At higher milling time, i.e. 50 h, the powder blend transformed to amorphous structure. This structural evolution was due to competing events of cold welding fracturing during high energy ball milling.Figure optionsDownload full-size imageDownload as PowerPoint slide