SHOCK CONSOLIDATION OF MECHANICALLY ALLOYED AMORPHOUS TI-SI POWDERS

Mechanical alloying was used to synthesize amorphous 5Ti-3Si atomic ra tio powders in a SPEX mill under Ar atmosphere. X-ray diffraction anal ysis revealed formation of a single-phase amorphous compound after abo ut 24 hours of milling. High-resolution transmission electron microsco py (TEM) showed that the milled powder still contained nanocrystallite s of Ti and Si among regions of generally amorphous compound. The mech anically alloyed amorphous powder was shock consolidated, using a plat e impact assembly, to produce bulk compacts. The compaction resulted i n a significant amount of crystallization, forming 30- to 40-nm crysta ls of TiSi2 and Ti5Si3 intermetallic compounds. The compacts were subs equently annealed above the crystallization temperature, measured to b e similar to 640 degrees C using differential thermal analysis. The co mpacts annealed at 800 degrees C for 1 hour showed only limited grain growth to similar to 50-nm crystallite size. Microhardness of the shoc ked amorphous alloy compacts was similar to 1100 KHN, which increased to similar to 1250 KHN upon subsequent annealing, with the formation o f a more homogeneous nanocrystalline microstructure.