Titanium borides deposited by chemical vapor deposition thermodynamic calculation and experiments

Abstract
The deposition conditions of titanium diboride and titanium monoboride were calculated under the thermodynamic equilibrium assumption and experimentally checked. The theoretical deposition diagram was calculated by the SOLGASMIX program. All the gaseous and condensed species were taken into account. The initial gas mixture was composed of titanium tetrachloride, boron trichlonde and hydrogen. The calculated diagram shows that low partial pressures of boron trichloride and titanium tetrachloride are both required in order to be able to deposit titanium monoboride. The deposition experiments were canied out at atmospheric pressure in a cold wall reactor. The substrates were either molybdenum or molybdenum coated by Tic. They were inductively heated by a RF coi1 to the deposition temperature (1473 K). Special devices were used to reach the low partial pressures of titanium tetrachloride and boron trichloride necessary to deposit titanium monoboride. The nature of the coatings were determined by X-ray diffraction and EPMA-WDS. Titanium dibonde as well as titanium monoboride was obtained by varying the composition of the initial gas phase. The hardness of TiB₂was measured by ultra low load indentation.