LOAD-ADAPTIVE CRYSTALLINE-AMORPHOUS NANOCOMPOSITES

Advances in laser-assisted deposition have enabled the production of h ard composites consisting of nanocrystalline and amorphous materials. Deposition conditions were selected to produce super-tough coatings, w here controlled formation of dislocations, nanocracks and microcracks was permitted as stresses exceeded the elastic limit. This produced a self-adjustment in the composite deformation from hard elastic to quas iplastic, depending on the applied stress, which provided coating comp liance and eliminated catastrophic failure typical of hard and brittle materials. The load-adaptive concept was used to design super-tough c oatings consisting of nanocrystalline (10-50 nm) TiC grains embedded i n an amorphous carbon matrix (about 30 vol%). They were deposited at n ear room temperature on steel surfaces and studied using X-ray photoel ectron spectroscopy, X-ray diffraction, scanning electron microscopy, Raman spectroscopy, nanoindentation and scratch tests. Design concepts were verified using composition-structure-property investigations in the TiC-amorphous carbon (a-C) system. A fourfold increase in the toug hness of hard (32 GPa) TiC-a-C composites was achieved in comparison w ith nanocrystalline single-phase TiC.