Effects of build orientation and heat treatment on the microstructure and mechanical properties of selective laser melted Ti6Al4V lattice structures

The metal additive manufacturing industry is rising and so is the interest in new lattice structures with unique mechanical properties. Many studies have already investigated lattice structures with different geometries and their influence on mechanical properties, but little is known about the effect of specific processing characteristics that are inherent to metal additive manufacturing. Therefore this study investigates the effect of two crucial steps in the manufacturing process: the build orientation selection and heat treatment. In total the microstructure and static mechanical properties of five different orientations and three heat treatment conditions were evaluated using Ti6Al4V diamond like lattice structures. The results show a significant decrease in mechanical strength for samples that are built diagonally and a transformation of the microstructure after a HIP (hot isostatic pressing) treatment, resulting in a lower maximum strength, but higher ductility. In general, horizontal struts should be avoided during manufacturing, unless the applied load after manufacturing can be properly supported by other struts. Both a stress relief heat treatment and a HIP treatment can be used in statically loaded applications, whereas a HIP treatment is believed to be beneficial for dynamically loaded applications. This study enables an appropriate selection of build orientation and heat treatment of lattice structures for different applications.