Abstract
The annual demand for bone scaffolds around the world has resulted in the urge and necessity to design or produce scaffolds that meet all the biological requirements such as good corrosion behaviour, porosity, and Young’s modulus that is close to that of the natural human bone. It is imperative that a proper choice of biomaterials and additive manufacturing procedures be made. This study explored the effect of different laser sintering parameters on the microstructural features of the Ti-6Al-4V reinforced with ZrO2. The ratio of the Ti-6Al-4V and ZrO2 powders was 95% and 5%, respectively. With the raw materials being in a powder form when received, a mixing procedure was adopted to efficiently mix the powders in preparation for the laser sintering method. In the mixing procedure, the rotation was 75 rpms, the duration 8 hours, and alumina balls were added to ensure homogeneity and break down of larger powder particles.
After the powders were mixed, they were laser deposited using a Direct Metal Laser Sintering technique with different parameters. Three different laser powers were used, which were 50W, 170W and 340W. These specific laser powers were used to be able to clearly investigate the impact of the power on the corrosion behaviour of the laser deposited samples. The speed was also varied, and they were 0.1 m/s and 1.0 m/s. The layer height of the powder also varied, and they were 100 and 120 microns. After the laser sintering method was completed, the samples were then exposed to the Hank’s Balanced Salt Solution (simulated human body system), which acted as a working electrode in the three-electrode system for the electrochemical tests. The three electrochemical techniques that were used were open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy. The potentiostat that was used was the Versa STAT 4.
The as received and mixed powders, laser deposited composites and samples that were exposed to the electrolyte were characterized using scanning electron microscopy (SEM) equipped with an Energy Dispersive X-Ray Spectroscopy (EDX) and X-Ray Diffractometry (XRD) which provides information on the phase identification. The results showed that varying laser sintering parameters does affect the microstructural features of the materials. Some of the samples showed to have unmelted particles, melt pools and pores, which were attributed to the different parameters. The OCP results were also different, with some of the samples having a more negative value and others a less negative value, which showed the tendency of the materials to corrode. The difference between the sample with the highest OCP and that with the lowest OCP is 20%. The potentiodynamic curves also showed the surface reactivity of the samples, whereby samples with higher corrosion potentials were more susceptible to corrosion than those with the lower corrosion potential. From the potentiodynamic curves, a Tafel extrapolation method was also applied to calculate the corrosion rates of each sample. Lastly, the corrosion mechanisms that took place in each sample was studied using the EIS measurement technique. From the corrosion tests, samples with low to moderate laser power (50 – 170 W) had lower corrosion rates.