CHARACTERIZATION OF THIN WALLED Ti-6Al-4V COMPONENTS PRODUCED VIA ELECTRON BEAM MELTING

Direct-metal energy beam SFF processes typically produce layers by scanning the contours and then filling in the area within the contour. Process parameters used to solidify contours are often different from those for fill areas. It is to be expected, therefore, that the contour and fill area regions will have different microstructures. This can have important ramifications for thin walled components such as biomedical implants whose slices have very little fill area. This paper characterizes the metallurgical differences in contour and fill areas in titanium components produced via Electron Beam Melting. The implications of these properties for thin walled components are described. Introduction Arcam's Electron Beam Melting (EBM) process (www.arcam.com) is a direct-metal freeform fabrication process that uses a 4.8 kW electron beam to selectively scan and melt layers of metal powder one on top of the next. Details of the process can be found in reference [1]. Titanium (Ti-6Al-4V) is an alloy that is receiving considerable interest for use with this process from industry. The EBM process was originally developed with the tool and die making industry in mind. Whereas the H13 tool steel components originally targeted with this process are typically large bulky parts, the titanium components built with the process tend to be thin walled in nature. For purposes of this paper, a thin walled part is a part with a thickness of approximately 14 mm. Representative thin-walled Ti-6Al-4V components built with this process include the turbocharger compressor wheel shown in Figure 1(a), the knee implant shown in Figure 1(b), and the bone plate shown in Figure 1(c). The vanes on the turbocharger wheel are approximately 1.2 mm thick, and the knee implant and bone plate each has an average thickness between 3-4 mm. Most beam-based freeform fabrication processes melt or otherwise solidify a raw material by scanning the contour of a given slice and then scanning the fill area inside of the contours. In the case of direct-metal freeform fabrication processes, it is not uncommon for different process settings to be used when solidifying contours versus fill area. This is done primarily for reasons of improving surface finish and appearance. As the solidification rate of the metal powder can be influenced by differences in process settings (e.g. beam power and scan speed), it is possible for the contours and fill area to have substantially different microstructure and mechanical properties.