Transient CVD experiments were produced from CH 3 SiCl 3 (MTS)/H 2 mixtures, by varying linearly as a function of time the deposition temperature or the initial gas flow rates (Q MTS or Q H2). The consequences on the composition of the gas phase, the deposition rates, and the physicochemical properties of the transient coating layers ( Tr) have been respectively examined by in situ FTIR, thermogravimetric analyses, Raman spectroscopy and TEM. Finally, the adhesion of SiC/ Tr /SiC bilayers, obtained using various transient stages, was investigated by scratch testing. For transient stages resulting from a decrease of Q MTS or T, crystallized or amorphous silicon can be co-deposited, due the higher reactivity of SiCl x radicals as compared to hydrocarbons. In this case, the continuous covalent bonding through the Si-rich interfacial layers preserves the strong adhesion between the two stoichiometric layers. Transient stages resulting from a decrease of Q H2 close to zero eventually lead to the co-deposition of anisotropic carbon, due to the formation of unsaturated hydrocarbons in the gas phase. The interfacial layers with the largest thicknesses and including a continuous anisotropic carbon interlayer lead to poor adhesion properties. Conversely, thin and discontinuous carbon-rich interfacial layers do not affect the interfacial properties significantly. Highlights  Systematic investigations of various CVD transient stages: f(T or H 2 /CH 3 SiCl 3)  Correlation between changes of CVD parameters and in situ gas phase composition  Correlation between CVD parameters and deposition rate  Correlation between CVD parameters and nature of the gradient Si-C coatings