STRUCTURE AND HARDNESS OF TIAL-TIB2 COMPOSITE PREPARED BY HOT ISOSTATIC PRESSING OF MECHANICALLY ALLOYED POWDERS

TiAl/5-50 mol%TiB2 composite materials and TiAl were prepared through solid state powder processing, consisting of the mechanical alloying where heptane, grinding aid, was added, and the hot isostatic pressing. (1) Ball-milling of the powder mixture of Ti and B for more than 50 h can produce mechanically alloyed compound powder composed of TiB2 and TiB. (2) The HIP sintered compact of the mechanically alloyed amorphous TiAl powder was composed of gamma-TiAl with a small amount of Ti3Al and Al2Ti4C2. Al3Ti, TiB and TiC appear via solid state reaction in the sintered composites of the powder mixture of amorphous TiAl and mechanically alloyed TiB2. The amount of TiAl, Al3Ti and Al2Ti4C2 in the composites decreased with an increase in the powder mixing ratio of TiB2 to TiAl, while TiB2 and TiC increased. The TiB2 phase in the composite structure is particle-dispersed as islands of 10-50 mum size. (3) The micro-vickers hardness of the sintered composite materials increased with an increase in the mixing ratio of the TiB2 powder to the TiAl one, and reached a maximum value of 1200 Hv at the TiAl/25 mol%TiB2 composition.