ABSTRACT
Ti-6Al-4V powder and parts from the electron beam melting (EBM) additive manufacturing (AM) process have been characterized. In the EBM AM process, preheating is applied and serves to aggregate the precursor powder and may affect the subsequent melting stage. Specimens with preheated Ti-6Al-4V powder enclosed and solid parts were fabricated and prepared for microstructural and morphological examinations. In addition, micro-CT scan analysis was conducted to study the powder porosity and powder size distributions. Moreover, the process parameters in EBM AM were
7.1 Introduction .......................................................................................................................... 180 7.2 Experimental Details ............................................................................................................ 181
7.2.1 Powder Analysis ....................................................................................................... 181 7.2.1.1 Raw Powder ............................................................................................... 181 7.2.1.2 Machine, Material, and Fabrication Parameters and Conditions .............. 182 7.2.1.3 Powder-Bed and Powder-Enclosed Samples .............................................. 182 7.2.1.4 Metallographic Method ............................................................................. 182 7.2.1.5 Micro-Computed Tomography Analysis ................................................... 182
7.2.2 Analysis of Part Microstructures .............................................................................. 182 7.2.2.1 Fabrication Parameters and Conditions ..................................................... 182 7.2.2.2 Build Height and Orientation Effects ........................................................ 183 7.2.2.3 Beam Speed Effect .................................................................................... 183 7.2.2.4 Metallographic Method ............................................................................. 183
7.3 Results and Discussions ........................................................................................................ 184 7.3.1 Powder ...................................................................................................................... 184
7.3.1.1 Raw Powder ............................................................................................... 184 7.3.1.2 Sintered Powder ......................................................................................... 184
7.3.2 Part Microstructures ................................................................................................. 189 7.3.2.1 Typical Microstructures of EBM AM Parts .............................................. 189 7.3.2.2 Height and Orientation Effects on Microstructures................................... 191 7.3.2.3 Scanning Speed Effect on Microstructures ............................................... 191
7.4 Conclusions ........................................................................................................................... 194 Acknowledgments .......................................................................................................................... 195 References ...................................................................................................................................... 195
investigated in build part microstructures. The results can be summarized as follows. Preheating results in metallurgical bonds or even partial melting of the powder and neck formations are clearly evident. Micro-CT scans show a porosity of 50% for the preheated powder in EBM AM. The microstructure of the Ti-6Al-4V build parts is characterized by a columnar structure of prior β phase along the build direction, and ne Widmanstätten structures and martensites are presented inside of the prior β. Uneven microstructures are noted along the build height; the top layers show ner microstructure while the bottom layers display a high percentage of α .ʹ Both the prior β grain size and α-lath thickness decrease with an increase of the scanning speed.
