Variable Oxidation & Defects In Ti-6Al-4V Material In Electron Beam Melting Additive Manufacturing

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Clark, Edward Patton
Digital Commons @ DU
Additive Manufacturing; CAD software; Finite Elemental Analysis; Materials Science and Engineering; Mechanical Engineering
thesis / dissertation description
Powder-based metal in additive manufacturing (AM) is advantageous for rapid prototyping of parts and components, with the benefit of reusing powder to reduce production costs. A common driver in the aerospace industry is free-form complex geometries which can be created using CAD software to optimize specifications with strength-to-weight ratios in components. Weight optimization of aircraft components using additive manufacturing reduces material, which significantly reduces production cost in comparison to cast and wrought metallic products. Large biomedical and aerospace industries heavily invest in feedstock metal powders that have low density under structural stresses and high temperatures, resulting in superior resistance to corrosion in extreme environments. The high strength-to-weight ratio material with long- term cost affordability obtained by AM process results in cost-efficiency of the Ti-6Al- 4V powder by recycling unspent powder material. However, while efficient, the recycling of titanium (Ti) powder in additive manufacturing results in micro-particle characterization, chemical, and mechanical changes due to indirect and direct environmental extremes. Direct exposure to high thermal heat during the electron beam melting (EBM) process after powder reclaiming can result in particle microstructure and chemical variations. Initial assessments of oxygen (O) wt% in bulk powder material was subsequently selected for further investigation as a characteristic for decline in mechanical properties of consolidated materials. A preliminary analysis of virgin, 5x-recycled, and artificially highly oxidized Ti-6Al-4V powder was conducted using Charpy impact testing on consolidated specimens from each wt% O in the bulk powder batches, and finite elemental analysis (FEA) to understand the build defect effect found in solidified Ti-6Al-4V material.