SHOCK CONSOLIDATION OF MECHANICALLY ALLOYED AMORPHOUS TI-SI POWDERS

Mechanical alloying was used to synthesize amorphous 5Ti-3Si atomic ratio powders in a SPEX mill under Ar atmosphere. X-ray diffraction analysis revealed formation of a single-phase amorphous compound after about 24 hours of milling. High-resolution transmission electron microscopy (TEM) showed that the milled powder still contained nanocrystallites of Ti and Si among regions of generally amorphous compound. The mechanically alloyed amorphous powder was shock consolidated, using a plate impact assembly, to produce bulk compacts. The compaction resulted in a significant amount of crystallization, forming 30- to 40-nm crystals of TiSi2 and Ti5Si3 intermetallic compounds. The compacts were subsequently annealed above the crystallization temperature, measured to be similar to 640 degrees C using differential thermal analysis. The compacts annealed at 800 degrees C for 1 hour showed only limited grain growth to similar to 50-nm crystallite size. Microhardness of the shocked amorphous alloy compacts was similar to 1100 KHN, which increased to similar to 1250 KHN upon subsequent annealing, with the formation of a more homogeneous nanocrystalline microstructure.