THERMOCHEMICAL MODELING OF THE CVD PROCESS OF TIN ON 316L STAINLESS-STEEL SUBSTRATE

A thermodynamic study was performed in order to determine the chemical interaction of a 316L stainless steel substrate with the gaseous spec ies present in a CVD reactor for the deposition of TiN. Thermochemical equilibria of the heterogeneous system were calculated by using a com putational technique based on the minimization of the free energy. The calculations were done considering the most severe case of reaction, i.e. for activities of alloying steel elements equal to unity. The tem perature was varied between 800 and 1100-degrees-C and the initial mol ar relationship, alpha = N2/TiCl4, between 0.1 and 2. The highest proc ess efficiency was obtained at temperatures greater-than-or-equal-to 9 00-degrees-C and N2/TiCl4 ratios greater-than-or-equal-to 0.7. The the rmochemical calculations demonstrated that 316L stainless steel is not inert with respect to the gaseous phase involved in the deposition pr ocess of TiN. The equilibrium diagram of the Ti-Cr-Mn-Fe-N-Cl system w as constructed, which allowed the appropriate partial pressure and tem perature conditions to carry out the deposition process to be determin ed. Thus, the formation of a liquid phase, deleterious from the adhesi on point of view, would be avoided. The corresponding equilibrium part ial pressures of the gases were valuable in determining which species were mechanistically important.