Synthesis, characterization and potential applications of amorphous coatings of titanium carbide and titanium diboride

Amorphous materials have an advantage over crystalline versions: the absence of grain boundaries reduces the probability of fracture and corrosion. However, many amorphous metal alloys crystallize at moderate temperatures, thus limiting their applications. One amorphous titanium carbide (TiC) film to be described did not crystallize until 1000 degrees C. The TiC film was synthesized by metal-organic chemical vapor deposition (MOCVD). The organometallic precursor molecule dissociated and left hydrogen and organic fragments which help stabilize the carbide with respect to crystallization and corrosion. The reason for its amorphous state-determined by X-ray diffraction (XRD) and transmission electron microscopy selected area diffraction (TEM/SAD)-was the low substrate temperature required, between 150 degrees C and 300 degrees C. Pure amorphous TiC and titanium diboride (TiB2) films were prepared by electron-beam vaporization (EBV) of single crystal chips onto liquuid-nitrogen cooled substrates; they crystallized at lower temperatures. All the films analyzed by extended X-ray absorption fine structure (EXAFS) and extended electron energy loss fine structure (EXELFS) exhibited short-range order but no long-range order, so they could still be described as "amorphous." Potential applications of these high hardness, high melting-point, corrosion-resistant, low-friction and diffusion-resistant coatings could include bearings, cylinder linings, microcircuits and biomedical implants.