TITANIUM BORIDES DEPOSITED BY CHEMICAL-VAPOR-DEPOSITION THERMODYNAMICCALCULATION AND EXPERIMENTS

The deposition conditions of titanium diboride and titanium monoboride were calculated under the thermodynamic equilibrium assumption and ex perimentally checked. The theoretical deposition diagram was calculate d by the SOLGASMIX program. All the gaseous and condensed species were taken into account. The initial gas mixture was composed of titanium tetrachloride, boron trichloride and hydrogen. The calculated diagram shows that low partial pressures of boron trichloride and titanium tet rachloride are both required in order to be able to deposit titanium m onoboride. The deposition experiments were carried 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 coi l to the deposition temperature (1473 K). Special devices were used to reach the low partial pressures of titanium tetrachloride and boron t richloride necessary to deposit titanium monoboride. The nature of the coatings were determined by X-ray diffraction and EPMA-WDS. Titanium diboride as well as titanium monoboride was obtained by varying the co mposition of the initial gas phase. The hardness of TiB2 was measured by ultra low load indentation.