||According to the previous results, Ti-6Al-4V possess better biocompatibility, bio-corrosion resistance and appropriate mechanical properties as compare with other Ti-based alloys. Additive manufacture has become a flourishingly and potentially technique in fabricating biomaterials due to some benefits. For an example, the elastic modulus of material which able to control by adjusting porosity or pore size. Comparing among traditional processing and additive manufacturing, the former shows complexity and higher cost in producing porous foam; the latter own benefits of lower time cost, budget, and well-designed products with input CAD data. However, inferior surface roughness of additive manufactured product not only influence the outward appearance but also reduce the corrosion resistance. |
Firstly, Ti-6Al-4V alloys are successfully produced by electron beam melting (EBM) and selecting laser melting (SLM). Based on XRD and EDS results, both Ti-6Al-4V alloys are confirmed as α-phase Ti-6Al-4V. By applying electropolishing polishing treatment, surface roughness of EBM sample is confirmed by 3D alpha-step as nearly 25 μm, 20 μm, 15 μm, 10 μm and 5 μm, while SLM sample as 15 μm, 10 μm and 5 μm. Through SEM observations, the as-fabricated EBM and SLM samples show surface morphology full of attached powder. However, the surface gradually transformed to terrace-like, field-like and wave-like morphology as results accompanied with decreasing of surface roughness after EP.
Electrochemical analyses of corrosion behaviour in simulating body fluid (SBF) is conducted. As compare among samples fabricated by similar AM method, the as-fabricated samples show highest Ecorr and Icorr, which indicate that a higher energy is needed to activate corrosion reaction. However, due to inferior surface properties of as-fabricated sample, more surficial defects display and a larger area which is easier to induce corrosion reaction, therefore a higher corrosion rate performed once the outer passive film is broken. Besides, the as-fabricated SLM sample shows better bio-corrosion resistance as compare with EBM, this may be contributed by a lower surface roughness of SLM sample. For samples with 15 μm surface roughness, EBM possess smaller Ecorr and Icorr. Which indicate that the passive layer formed as reacted with electrolyte solution is not good as the passive layer initially formed, and the relatively worse morphology of SLM sample is benefit in promote corrosion reaction once the protective layer is broken. However, for samples with 10 μm surface roughness, EBM sample show better bio-corrosion behaviour as higher Ecorr and smaller Icorr. This is due to formation of denser and more completely passivated oxide layer after a prolonged EP duration, and the surface with less defects is benefit in lower the corrosion rate. Worth noting that, EBM sample with 5 μm roughness shows large area of pitting traces, this may due to an over-polishing during EP. Because of this situation, the mentioned EBM sample is not suitable to compared under electrochemical analysis, and reasonably be restrain in bio-implantation.