Effects of fabrication conditions on mechanical properties of Ti-6Al-4V fabricated by powder bed fusion additive manufacturing
At the writing of this thesis, additive manufacturing (AM) also known as 3D printing, has been popularized for its diversity in applications ranging from home and personal use, medical, industrial, consumer products, aerospace, architecture, automotive, military, fashion, food, art and more. Industries taking advantage of the design freedom and complexity offered by AM have exploded the growth of the technologies. Specifically, technologies that process metals using electron and laser beams have been recognized by the aerospace industry as a promising avenue for re-engineered components leading to reduced weight and improved engineering efficiencies for components like engine brackets and nozzles. However, the direct implementation of AM has not been straightforward primarily because AM processes are not fully trusted to produce reliable and reproducible parts. Continued research, including the subject of this thesis, is aimed at better understanding process variations in the AM of metals via powder bed fusion. Electron Beam Melting (EBM) is an AM is a technology in the category of powder bed fusion that is seeing increased adoption by a variety of industries for part production. EBM was the focus of this study for the fabrication of solid and porous parts using precursor powder composed of Ti-6Al-4V. This research is centered on evaluating mechanical properties, analyzing microstructures, and correlating the fabrication process to inherent characteristics of solid and porous parts fabricated utilizing EBM. For dense parts, data were documented on the effects on mechanical and microstructural properties from neighboring parts and building location. In the case of porous, or lattice structures, data were documented on the effect of parameter modifications, such as processing currents and number of scan passes, on the final part mechanical response and microstructure. Solid and lattice components were mechanically tested and microstructural features were obtained by the use of computer software MATLAB. Microstructural and factographic analyses were performed on samples prepared for such analysis and the prepared surfaces were used for hardness testing. Several variables in part production exist for AM, including, but not limited to, part orientation, part location, processing parameters, and geometry. For the solid components fabricated for this thesis, the core objective was to determine the effect that surrounding parts have on mechanical properties. The study was expanded to also determine how part location within a build area affects the mechanical properties. The fabrication of generic structures provided the information on features produced using the standard commercial methodology, which would generally be used by industry. One of the benefits provided to Arcam users is the ability to access the process menu for customize build parameters. The previous deigns presented a study on features for solid structures fabricated without processing parameter variations. This furthering task presents for modification of processing parameters on lattice structures. The area that has been studied adds to improvements on features by additive manufacturing in general, enabling sophisticated designs with tailored properties while optimizing material and weight. A particular focus of this research was the study of lattice structures fabricated by EBM. Mechanical information of a material was obtained through compression testing, which provided values for the following properties: young’s modulus of elasticity (E), ultimate compression strength (UCS), the fracture load, and the displacement seen at such. Twenty-seven total lattice specimens were fabricated and tested. A correlation between microstructure and properties was explored using metallography analysis. Samples that displayed considerable property differences within a single build were chosen for analysis and consequently subjected to hardness testing. Fractography analysis was also performed on selected specimens to examine the potential cause(s) contributing to the bimodal failure mode. Overall, the research outcome of this thesis provided further characterization of the EBM fabrication process and presented some potential improvements to unique lattice structures. The mechanical response obtained by increase of surface area and varying locations showed that certain variations are present and users need to be aware of these part-to-part differences. In the case of components containing lattice structures, the mechanical response obtained by variation of the processing current within a single build and increasing scan passes suggested that detrimental martensite phase that typically occurs in the standard build process can be removed from in-process modifications. (Abstract shortened by ProQuest.)
Azani, Paola, "Effects of fabrication conditions on mechanical properties of Ti-6Al-4V fabricated by powder bed fusion additive manufacturing" (2016). ETD Collection for University of Texas, El Paso. AAI10124184.