Investigating microstructure and defects evolution in laser deposited single-walled Ti6Al4V structures with sharp and non-sharp features

Abstract

The laser directed energy deposition (laser-DED) Additive Manufacturing (AM) has unique capability of being able to deposit functional geometries on existing components. Many times the required geometries contain sharp features such as abrupt turns. During deposition such features introduces heterogeneity in the build-part and adversely the structural integrity of the part. The slower deposition speeds due to the deceleration and acceleration of the motion controller around sharp features in a geometry leads to defects such as variable wall thickness, porosity, lack of fusion, and cracks. In many cases, the functional geometries are single-walled and there is not enough material volume to machine the deposited material. Such cases pose a unique challenge to the laser-DED techniques capabilities. In this work, single walled cubical Ti6Al4V structure with sharp and rounded corners were fabricated using laser Directed Energy Deposition (DED). Cross sectional and build plane coupons were extracted from each sample for microstructure and defect analysis. Results show that inclusion of small rounded corners (radii of 0.5 and1.0 mm) leads to consistent deposition speeds. Defect density measurements, using optical microscope, showed reduction of defects from 6.8 ± 0.35 % to a virtually defect-free structure for samples with the rounded corners. The results also indicated that consistent deposition speed around rounded corners improved homogeneity in the resulting microstructure as compared to the geometry with sharp corners when processed under identical parameters.