Process parameter interaction effect on the evolving properties of laser metal deposited titanium for biomedical applications

The laser power interaction effects on the evolving properties of commercially pure titanium during Laser Metal Deposition were analyzed. The optimized processing parameters obtained for this research study were, spot size of 4 mm, powder flow rate of 2 g/min, gas flow rate of 2 l/min, and the scanning speed set at 0.002 m/s. A total of seven samples were fabricated by depositing titanium powder onto a Ti-6Al-4V base metal; using an Nd-Yag laser by varying the laser power from 400 to 1600 W while keeping all the other parameters constant. The deposited samples were characterised through the evolving microstructure, microhardness, wear and the corrosion behaviour. The microstructural evaluation revealed that the ratio of dilution increased with an increase in the laser power. Furthermore, it was found that as the dilution increased, the wear resistance behaviour of the deposits decreased due to the increased foreign elements (Al and V) from the substrate which inhibited smooth fusion as the molten deposit cooled. Also, the microstructural evaluation showed that finer martensitic microstructures were obtained at lower laser power rating which was associated with inter-layer porosity and due to the low laser-material interaction. However, Widmanstätten structures were observed at higher laser power settings together with the presence of intra-layer porosity which is desirable for osteointegration. For biocompatibility, immersion tests in the Hank's solution were conducted for 14 days. The atomic absorption spectroscopy analyses showed that no leaching happened during the immersion process for all the samples hence, confirming the desirable properties expected of biomedical implants. An overall overview on the effects of the laser power which has a significant effect on the evolving properties is essential in order to know how this process parameter can be controlled to attain certain properties of the material for specific and tailored functions.