Effect of surface conditioning on the flowability of Ti6Al7Nb powder for selective laser melting applications

Porous metallic implants have been developed to provide a good implant–tissue mechanical attachment and an as close as possible elastic modulus to that of human bone, by the means of a proper porosity. A viable manufacturing technology for personalized implants is rapid prototyping (RP), which employs fine feeding powders which usually display a poor flow behaviour. In the present work, the required flowability of Ti6Al7Nb powder aimed for selective laser melting (SLM) applications was improved by applying a simple heat treatment in air, at temperatures higher than 500 °C. As flowability depends on the powder surface condition, the surface chemical composition before and after heat treatment was characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis. The results indicated that the amount of basic and acidic –OH groups is almost the same for powders treated at 400 °C, which do not flow, and powders treated at 500 °C, which display flowability. An increase of the Al2O3 amount in the TiO2-based surface layer on the powder particles with the treatment temperature was noticed. Based on the results, the temperature of 500 °C was selected for the further research. The conditioned powder displayed a very good technological behaviour, being successfully used for obtaining specimens with both cellular and fully dense structures through SLM. The microstructure of the manufactured samples, characterized by optical microscopy and scanning electron microscopy (SEM), has shown mainly α′ martensite, with columnar grains.