Tailoring grain structure and mechanical properties of Ti6Al4V via EB-PBF using an advanced point melt strategy

Tailoring the mechanical properties of a part is a very desirable feature which could be realised using additive manufacturing (AM). In electron beam powder bed fusion (EB-PBF) the option of using point melt strategies opens the possibility of creating advanced thermal conditions during printing, which could control the solidification process. This paper aims at using a new point melt strategy developed by Colibrium Additive to investigate its impact on microstructure and mechanical properties. In this strategy, the main parameters for different process conditions are the inhibition time and inhibition radius where the main change would be the background temperature. A total of 45 Ti6Al4V samples with 15 different melt conditions obtained by changing these two parameters were printed. The results show a clear relationship between the parameters in the point melt algorithm and the mechanical properties, with yield strength among the highest found for EB-PBF printed Ti6Al4V in present literature. High background temperature decreased the strength but increased the ductility, while low background temperature increased the strength. Larger alpha grains and colonies could be seen for samples printed with high background temperature and as the background temperature decreased, these grains decreased in size. The increase in strength is attributed to the decrease in alpha lath size in combination with more columnar primary beta grains.Samples printed with lower background temperature also exhibited defects which could be due to the decrease in melt pool overlap or placement on the build plate. This work demonstrates the possibilities of using advanced melt strategies, showing that significant differences in mechanical properties can be achieved simply by changing the order in which single points are melted. • Advanced point melt strategies tailor microstructural and mechanical properties. • Yield strength varied between 1060 MPa and 1170 MPa. • Mechanical differences were correlated with alpha-phase characteristics. • Heat simulations show the influence of background temperature during print. • EBSD correlated background temperature with grain size, yield strength and elongation.