Microstructure and mechanical properties of metal-alloy nitride (M IMII)N overcoats for rigid disks

Mechanical durability and microstructures are investigated for metal alloy nitride overcoats consisting of (M_IM _II)N, where M_I=Ti or Zr and M _I=V, Nb, or Ta. The overcoats are prepared by conventional reactive RF sputtering. It is demonstrated that stoichiometric nitrides are formed for a nitrogen content at or higher than 50 vol.% in a nitrogen-argon gas mixture during deposition. The average grain sizes of Zr-based alloy nitrides are 4 to 5 nm, while those of Ti-based alloy nitrides are 10 to 13 nm. The mechanical durability of the Zr-based alloy nitrides is much higher than that of the Ti-based ones. Overcoats of (Zr_1-xNb_x)N show the highest durability; this occurs at a Nb content, x, of 0.4 to 0.6. Zirconium-niobium nitrides exhibit a durability higher than that of conventional carbon overcoats in both pin-on-disk and continuous slow-grinding tests. This is due to the smaller grain size and more durable oxidized surface layer in the zirconium-niobium nitride films. The zirconium-alloy nitride overcoats thus exhibit the most promising mechanical properties for rigid-disk application