In the present study, the effects of phase transformations on the structure and mechanical properties of TiSiCN coatings were investigated. TiSiCN nanocomposite coatings were deposited on AISI H13 hot-work tool steel by a pulsed direct current plasma-enhanced chemical vapor deposition process at 350 or 500 degrees C, using TiCl4 and SiCl4 as the precursors of Ti and Si, respectively, in a CH4/N-2/H-2/Ar plasma as the source of carbon and nitrogen and reducing environment. Some samples deposited at 350 degrees C were subsequently annealed at 500 degrees C under Ar atmosphere. Super hard self-lubricant TiSiCN coatings, having nanocomposite structure consisting of TiCN nanocrystals and amorphous carbon particles embedded in an amorphous SiCNx matrix, formed through spinodal decomposition in the specimens deposited or annealed at 500 degrees C. In addition, it was revealed that either uncomplete or relatively coarse phase segregation of titanium compounds was achieved during deposition at 350 degrees C and 500 degrees C, respectively. On the contrary, by deposition at 350 degrees C followed by annealing at 500 degrees C, a finer structure was obtained with a sensible improvement of the mechanical properties of coatings. Accordingly, the main finding of this work is that significant enhancement in key properties of TiSiCN coatings, such as hardness, adhesion and friction coefficient, can be obtained by deposition at low temperature and subsequent annealing at higher temperature, thanks to the formation of a fine grained nanocomposite structure. (C) 2018 Elsevier B.V. All rights reserved.