EFFECT OF ALLOYING ADDITION ON STRUCTURE AND THERMAL-STABILITY OF TI40AL60 PREPARED BY MECHANICAL ALLOYING

Ternary (Ti40Al60)(100-x)M(x) (X=5-15at%, M=Mo, Nb) alloys have been prepared by Mechanical Alloying, and the process was monitored by X-ray diffraction technique. The effects of a third additional element have been examined concerning the alloying process, structure and phase thermal stability. As already observed in Ti40Al60 matrix prepared with the same conditions, an amorphous alloy was obtained at the end of the process. A different solubility of Mo (very limited) or Nb (total dissolved) into the matrix was detected. Upon thermal treatment the third element addition caused, in both cases, an increased crystallization temperature with respect to the matrix. The more detailed investigation on niobium addition (5-10at.%) evidenced the following path for powder crystallization: amorphous-disordered Al-ordered L1(0) phase. The evolution of the long-range order parameter revealed that the disorder --> order transition is favoured due to the presence of Nb, but independent of its concentration.