Thick boride coatings by chemical vapor deposition

The authors describe an experimental study of the chemical vapor deposition (CVD) of TiB2 by the hydrogen reduction of TiCl4 and BCl3 with the purpose of obtaining very thick (more than 100 μm) and uniform coatings. The optimum deposition conditions were as follows: temperature, 900-9500C; source gas ratios, [Ti]/[B] = 1/2 and [H]/[Cl] = 6/1. With these conditions, deposition rates greater than 25 μm h-1 were obtained. The composition was very uniform with an excess of boron over stoichiometry (probably in the form of free boron). A small amount of chlorine remained incorporated in the deposit probably as TiCl2 (0.05 wt.% at 9500C). The coatings were very hard (about 3700 kgf mm-2) and hardness was uniform through the thickness. With careful control of the deposition parameters, the CVD of uniform coatings with thickness of 1 mm or more appears feasible. (Auth.)