PORE FORMATION DURING REACTIVE SINTERING OF EXTRUDED TITANIUM ALUMINUM POWDER MIXTURES

A powder mixture Ti-49 at.% Al was extruded at room temperature. Swelling due to phase transformation during annealing was studied using differential scanning calorimetry and dilatometry. It is the result of several processes: (i) Kirkendall pores during solid state interdiffusion, (ii) macro-pores during the reaction of liquid aluminium and solid titanium, (iii) interdiffusion of Al3Ti and pure titanum forming the intermetallic phases gamma-TiAl and alpha2-Ti3Al. Swelling is anisotropic due to the elongated titanium particles. Sintering occurs at higher temperatures depending on the microstructure after Al3Ti formation. For technological applications, minimization of porosity is possible by optimization of the time - temperature path.