Manufacturing of YbAG coatings and crystallisation of the pure and Li2O-doped Yb2O3–Al2O3 system by a modified sol–gel method

In addition to their widespread use as optical scintillators, recent research has shown that garnet structures, such as YAG (Y3Al5O12), may be promising candidates as thermal barrier coatings (TBCs), or as oxidation or erosion resistant materials. We report here for the first time the fabrication of YbAG (Yb3Al5O12) garnet coatings via a relatively low temperature sol–gel technique. Crystallisation under the firing temperature up to 800 °C of a pure and Li2O-doped Yb2O3–Al2O3 system was investigated on single crystal Si(1 0 0) and steel substrates. A single-phase polycrystalline YbAG garnet film was manufactured for the first time at the comparatively low temperature of 700 °C. This is in contrast with traditional sintering methods that require at least a temperature of 1600 °C to produce YbAG garnet ceramics. When coated on a hardened steel substrate, a mesoporous surface with a relatively high hardness is produced. The thermal behaviour of the processing method was analysed by DTA and the structure of coatings was characterised by XRD, SEM and XPS. Such films may have widespread application as a wear-resistant TBC.