Enamelled coatings produced with low-alkaline bioactive glasses

Enamelling is a relatively easy and inexpensive technique to produce glass coatings. In this contribution, three different low-alkaline bioactive glasses, modified with Na2O and/or K2O for a total alkaline content of 4.6 mol%, were enamelled on Ti6Al4V substrates for potential orthopaedic applications. The glasses in powder form were applied by means of a precipitation-based method and thermally treated in the 800–850 °C range; in particular, the enamelling temperature required to obtain uniform coatings increased with increasing K2O amounts. The SEM observation revealed that the coatings were about 100 μm thick, with a crack-free interface with the metal substrate mediated by the development of titanium oxides. Even if the low-alkaline glasses are characterised by a high crystallization temperature, the coatings underwent a partial devitrification, especially in the presence of K2O. However, the development of bioactive crystalline species, such as wollastonite, was ben- eficial, in that the new phases not only improved the local mechanical properties (in terms of Vickers microhard- ness, from 232.1 ± 76.8 HV for the Na2O-modified glass coating to 317.9 ± 48.8 for the K2O-modified one), but still preserved the apatite-forming ability in a simulated body fluid.