Optimization of SLM Process Parameters for Ti6Al4V Medical Implants

Ti6Al4V alloy has received a great deal of attention in medical applications due to its biomechanical compatibility. However, the human bone stiffness is between 10 and 30 GPa while solid Ti6Al4V is significantly stiffer, which would cause stress shielding with the surrounding bone which can lead to implant and/or the surrounding bone’s failure. In this work, the effect of SLM process parameters on the characteristics of Ti6Al4V samples, such as porosity level, surface roughness, elastic modulus and compressive strength (UCS), has been investigated using Response Surface Method (RSM). The examined ranges of process parameters were 35-50 W for laser power, 100-400 mm/s for scan speed and 35-120 µm for hatch spacing. The results showed that the porosity % of a SLM component could be increased by reducing the laser power and/or increasing the scan speed and hatch spacing. It was also shown that there was a reverse relationship between the porosity level and both the modulus of elasticity and UCS of the SLM part. In addition, the increased laser power resulted in a substantial decrease of the surface roughness of SLM parts. The process parameters have been optimized to obtain structures with properties very close to that in human bones. Results from the optimization study revealed that the interaction between laser process parameters (i.e. laser power, laser speed, and the laser spacing) have the most significant influence on the mechanical properties of fabricated samples. The optimized values for the manufacturing of medical implants were 49 W, 400 mm/s and 99 μm for the laser power, laser speed and laser spacing, respectively. The corresponding porosity, surface roughness, modulus of elasticity and UCS were 23.62%, 8.68 µm, 30 GPa and 522 MPa, respectively.