An Electron-Microscopy Analysis of the Gradient Structure Formed in Titanium During Deposition of a Hard Coating

A titanium nitride coating 0.5 μm in thickness is deposited on specimens of VT1-0 technical-grade titanium using a vacuum-arc, plasma-assisted process. The formation of a multilayer, multiphase highly defective structure is observed, whose thickness reaches up to 40 μm. Surface and transition layers are determined from the morphological characteristics. It is shown that the surface layer (300–350 nm thick), where the major phase is TiN, possesses polycrystalline structure (crystallite size is 20–50 nm). The transition layer, whose major phase is Ti₂N, is divided into two sublayers. The sublayer immediately adjacent to the surface layer has columnar structure (transverse cross section of the columns is 50–80 nm). The sublayer bordering the bulk of the specimen is formed by quasi-equiaxed crystallites (150–280 nm). The main reason for formation of the multilayer, multiphase structure is thought to be the multistage character of material modification under conditions of common vacuum.