Study of the variation in microstructure, texture and mechanical properties of additive manufactured Ti-6Al-4V builds

In the electron beam melting powder bed fusion (EBM-PBF) build process, the metal alloy is exposed to extreme and complex temperature rates caused by cyclic ‘layer-by-layer’ deposition, melting, solidification and phase transformation processes. For example, the value and range of thermal gradients (10⁴-10⁷ K/m) during the EBM-PBF build process depend on many process parameters, such as input power, beam scan velocity, beam fill patterns, build height, and cooling rate, to name a few. These parameters have therefore a direct influence on the final microstructure and affect the properties as well as performance of the build.

Here, we investigate and quantify the effect of three different EBM-PBF beam fill patterns on the the microstructure, texture and mechanical properties of Ti-6Al-4V (Ti64) builds. Site-specific scanning electron microscopy (SEM) and electron backscattered diffraction (SEM-EBSD) experiments were performed to study microstructural variations across the AM build plane and along the AM build direction. SEM images were analyzed using image processing algorithms to extract statistically significant microstructural features, such as α lath thickness, width of residual β grain and the α /β phase fraction. Furthermore, EBSD data was used to analyze the size and texture of the prior high-temperature β grain, reconstructed based on Burgers orientations of room temperature α variants. Finally, Vickers microhardness data is obtained from each sample in the AM build plane and along the AM build direction to understand the processing-microstructure-property relationship.