Titanium aluminide composites produced by laser melting

Abstract

The microstructures of titanium aluminide based composites have been investigated using optical microscopy, scanning electron microscopy, energy dispersive spectrometry, transmission electron microscopy, and scanning transmission electron microscopy. The composites were in the form of pellets of ∼3 mm dia. produced by laser melting various mixtures of titanium, aluminium, and silicon carbide using 800 W laser power, 3 mm beam diameter, and 0·5 s pulse time. In all the processed samples, titanium and aluminium were completely melted and formed an alloy, whereas, SiC particles were partially dissolved leading to the enrichment of the alloy matrix with silicon and carbon. The aluminium contents of the matrixes of the composites spanned the range from ∼15 to ∼78 at.-%. In the 15–42 at.-%Al range, the phases formed during solidification were β titanium solid solution, TiC, and Ti₅(Si,Al)₃; β and Ti₅Si,Al)₃ occurred together as a eutectic constituent. During solid state cooling, β phase transformed to either martensite or an α₂ + γ mixture, depending on the aluminium content of the matrix. At 57 at.-%Al the matrix solidified to form γ, TiC, and Ti₅ (Si,Al)₃. The composite with 78 at.-%Al contained dendrites of Ti(Al,Si)₃ and interdendritic aluminium solid solution. Features of the Ti–Al–Si–C phase diagram are discussed in relation to the microstructures.

MST/1841