Results and discussion
The SEM micrographs from both, the top surface and of the cross section of the coatings are shown in Fig. 1. In Fig. 1A cracking due to the mismatch in thermal expansion coefficients (αTi6Al4V=9.7×10−6 K−1), (αcoating=14.2×10−6 K−1 and Δα=4.5×10−6 K−1) can be seen. In order to avoid the cracking, Ti–6Al–4V plate was precoated with the BLG (αBLG=11×10−6 K−1) which has a thermal expansion coefficient between the coating and the Ti–6Al–4V plate (Fig. 1B). As a consequence, no cracking in the biocide coating on Ti–6Al–4V previously coated with BLG is observed. The thermal expansion coefficients of 3Y-TZP (α3Y-TZP=10.6×10−6 K−1) and the biocide coating are quite similar, so in this particular case no cracking was observed (Fig. 1C). The study of the cross section reveals that the direct biocide coating on Ti–6Al–4V plate (Fig. 1D) is not mechanically stable showing a multicracking pattern. Conversely, in the particular case of Ti–6Al–4V plate precoated with BLG, no crack was detected and a strong adherence to the plate is observed (Fig. 1E). This strong interface has been reported to be due to the formation of Ti5Si3 compound [10] and [11]. On the other hand, the interfase 3Y-TZP/biocide coating is mechanically stable and the coating is well adhered to the substrate (Fig. 1F).