Abstract
Additive manufacturing [AM] offers the potential for advanced direct digital manufacturing of complex geometries that are challenging to fabricate using conventional manufacturing techniques. Dual laser SLM delivers the advantage of reduced manufacturing cycle times common to single laser SLM. However, in SLM manufacturing, careful process control is required, and unique flaws associated with SLM are significant obstacles to obtaining optimized mechanical properties. In this study, the microstructures and fracture surfaces for grade 5 titanium materials were characterized. Single laser and dual laser (with a misaligned build plate) SLM tensile tested specimens were compared, along with conventionally manufactured annealed Ti-6Al-4V round rod as a baseline. Finally, an analysis was performed to determine trends between the microstructures and fractures of single and dual laser (misaligned) additive manufactured grade 5 titanium and the mechanical test results from the previous study.It was demonstrated that the single laser maximum strength increases versus annealed rod (1205 MPa versus 895 MPa) and lower minimum ductility (1.9 versus 10) annealed rod correlates with the development of a martensite structure versus alpha plus beta structure in the annealed rod. The fast SLM heating and cooling rates provide the additional advantage of the equivalent of a strengthening heat treatment due to the formation of a martensite structure, also the large non-bonded region in the dual laser (misaligned) samples correlated with consistently low tensile strengths (171 ± 6 MPa) and low ductility (0.15 to 0.5%). The smaller and less consistent non-bonded areas resulted in higher strengths (905 ± 300 MPa) and higher ductility (1.9 to 3.0%) along with greater variation in the strengths (± 300 MPa for single versus ± 6 MPa for dual). It was concluded that fracture behavior and microstructures of the dual laser (misaligned) and single laser Ti-64 samples can be qualitatively correlated with mechanical strength and hardness.