## 3 Results and Discussion
### W-TCP Eutectic
The crystalline form of this material is composed by two phases: a bioactive phase capable of transforming into hydroxyapatite in contact with the physiological medium and wollastonite, whose dissolution generates a network of interconnected pores. The glassy form shows quick formation of a hydroxyapatite layer on its surface when they are immersed in SBF, due to the release of calcium and silicon ions during the first stage of immersion and the formation, in a second step, of an amorphous layer rich in silicon that provides nucleation points for the apatite crystals. It is expected that in the glass-ceramic material, the higher solubility rate of the amorphous phase leads to the formation of an interconnected porous structure of residual apatite [20]. Mechanical characteristics of these materials were measured by indentation technique and bending test. The results are given in Table 1.  
The low resistance of the crystalline rod is due to the presence of cracks caused by the high thermal gradients inherent to the solidification process and the difference in thermal expansion coefficients of both phases (\(\alpha_{\rm W}\) = 6.5 \(\times\) 10\({}^{-6}\)\({}^{\circ}\)C\({}^{-1}\)[21] and \(\alpha_{\rm TCP}\) = 14.2 \(\times\) 10\({}^{-6}\)\({}^{\circ}\)C\({}^{-1}\)[22]). The rods containing a glassy phase can adjust in a better way the internal stresses upon solidification and relieve them under annealing because of their plasticity at high temperature. The best results in flexural strength are achieved in the fully glassy rods. Hardness and toughness are less dependent on microstructure, as seen in Table 1.  
As the cracks emerge from the surface during the bending test, an increase in the flexure strength has been achieved with a laser surface remelting of the crystalline rods. This treatment generates a superficial glass layer capable of closing the cracks and at the same time can be used to modify the surface bioactivity. Figure 5a shows optical and SEM micrographs corresponding to longitudinal and transverse cross sections of eutectic \begin{table}
\begin{tabular}{c c c c} \hline
**Material** & **HV (GPa)** & **Toughness (MPa m\({}^{1/2}\))** & **Flexural Strength (MPa)** \\ \hline Crystalline & 4.6 \(\pm\) 0.45 & 1.39 \(\pm\) 0.3 & 73.8 \\ \hline Glass ceramic & 5.1 \(\pm\) 0.78 & 0.99 \(\pm\) 0.28 & 82.3 \\ \hline Glass & 4.9 \(\pm\) 0.18 & 1.08 \(\pm\) 0.12 & 310 \\ \hline \end{tabular}
\end{table} 
Table 1: Mechanical properties of W–TCP rods with different microstructure. rods remelted by laser, at 300 mm/h. A rotation of 200 rpm was applied to the rod to homogenize the distribution of energy provided by the laser on its surface. The flexural strength of the glazed eutectic rod after being annealed was 129 MPa. This value indicates, therefore, that the glass surface formation strengthens the crystalline eutectic rods. The flaws are arrested by the glass layer, as shown in Figure 5b, hindering the rapid crack propagation during the bending test. Figure 5c shows the cross-section of a eutectic rod with multiple flaws with details of the microstructure at the center and edge of the rod. As ceramic fracture is a process of crack nucleation and propagation, this processing approach could be exploited in many technological applications where ceramics and glasses are used, allowing these materials to be used in a more reliable way. In Figure 4d, the fracture section of a glazed eutectic rod is shown, displaying the crack that caused the failure.