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 β grains, with the width in the range of about 40–110 µm, 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 µm. 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 α-lath. However, the porosity defect on the build surface also becomes severe at the highest scanning speed (689 mm/s).