Research On Oxidation-resistant Self-spalling Lead-free Glass-ceramic Coating For Heat Processing Of Ti-6Al-4V Alloy

The oxidation is a serious problem during the heat processing of titanium alloys in air. Nowadays a variety of oxidation-resistant coatings have been widely used in reducing surface oxidation of Ti alloys. Unfortunately, conventional oxidation-resistant coatings can only provide a relatively narrow protection temperature range, and usually contain a considerable amount of lead, which is environmentally harmful.In present study, a lead-free self-spalling glass-ceramic coating with wider protection temperature range was developed to protect Ti-6Al-4V alloy from oxidation via a common dip-coating route. The starting materials for preparing dip-coating slurry are SiO₂, Al₂O₃, H₃BO₃, CaCO₃, Na₂CO₃, K₂CO₃, MoO₃, Li₂CO₃, TiO₂ and MgO powders.The oxidation-resistant effect was evaluated by comparing the Ti-6Al-4V specimens with and without protective coating, holding at different temperatures for 2 h in air. The metallographs of cross-sections were observed, and the depths of oxidized layers were determined by microhardness analysis. The changes of crystalline phase in coating at various soaking temperatures were investigated by means of XRD. The results show that the present glass-ceramic coating can provide not only the oxidation-resistant effect over the temperature range of 500¹000℃in ambient air, but also the capability of self-spalling from Ti alloy surface during cooling process after heat processing, with an environmentally friendly lead-free coating composition.