New metastable materials can be deposited using low temperature physical vapour deposition (PVD) techniques. During reactive sputtering, the atoms condensing in an intermixed state attempt to achieve a stable configuration. Due to low mobility of the adatoms, equilibrium phases cannot form and metastable structures are observed. Reactive sputtering can be used to deposit films with different stoichiometries and structures in the W-N system. The metastable phases α-W. β-W. W2N and WN1−x are obtained. All coatings are, however, thermally unstable. At temperatures above 570 °C. all phases are transformed into the a-W modification. By alloying chromium to the coatings in the W-N system, it is possible to stabilize all tungsten and tungsten nitride modifications as well as the interface layer between the substrate and the thin films.