In the present work, a pack cementation (PC) process was carried out to codeposit Cr and Si on a Nb substrate, Three masteralloy compositions (Cr36.4Si63.6 (A), Cr44.5Si55.5 (B) and Cr14.3Si85.7 (C)) were tested in the presence or absence of an activator (CrCl3 or SiCl4). The study of deposition mechanisms was undertaken through thermodynamic and dynamic calculations. Si appears to be deposited due to disproportionation reactions of lower halides, SiCl2 and SiCl3, while Cr seems to be transported by a molecular species containing Cr and Si, not yet identified.