Beam speed effects on Ti-6Al-4V microstructures in electron beam additive manufacturing

The effect of the beam scanning speed on part microstructures in the powder-bed electron beam additive manufacturing (EBAM) process was investigated in this research. Four levels of the beam speed were tested in building EBAM Ti-6Al-4V samples. The samples were subsequently used to prepare metallographic specimens for observations by optical microscopy and scanning electron microscopy. During the experiment, a near-infrared thermal imager was also used to acquire build surface temperatures for melt tool size estimates. It was found that the X-plane (side surface) shows columnar prior beta grains, with the width in the range of about 40-110 mu m, and martensitic structures. The width of columnar grains decreases with the increase of the scanning speed. In addition, the Z-plane (scanning surface) shows equiaxed grains, in the range of 50-85 mu m. The grain size from the lowest beam speed (214 mm/s) is much larger compared to other samples of higher beam speeds (e. g., 376-689 mm/s). In addition, increasing the beam scanning speed will also result in finer a-lath. However, the porosity defect on the build surface also becomes severe at the highest scanning speed (689 mm/s).