PORE FORMATION DURING REACTIVE SINTERING OF EXTRUDED TITANIUM ALUMINUM POWDER MIXTURES

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