Mamidala, RamuluBin Abdullah, Mohammad Sayem2026-04-202026-04-202026BinAbdullah_washington_0250E_29207.pdfhttps://hdl.handle.net/1773/55529Thesis (Ph.D.)--University of Washington, 2026Titanium alloys, particularly Ti-6Al-4V, are widely used in aerospace, biomedical, and other high-performance industries due to their exceptional strength-to-weight ratio, corrosion resistance, and biocompatibility. With the advent of metal additive manufacturing (AM), Electron Beam Powder Bed Fusion (EB-PBF) has emerged as a promising technology for fabricating Ti-6Al-4V parts with complex geometries and minimal residual stress with no gas interruption inside the build chamber. The mechanical properties, such as tensile strength and fatigue strength of EB-PBF Ti-6Al-4V are comparable to conventionally processed Ti-6Al-4V. However, limited research exists on its tribological performance of EB-PBF Ti-6Al-4V, specifically, wear and erosion behavior, in relation to process-induced variability and powder reuse. While EB-PBF components are adopted in wear-critical structures in aerospace, biomedical, and possibly oil-and-gas industries, limited knowledge of its tribological properties remains a major drawback.This dissertation addresses these critical knowledge gaps by providing a comprehensive investigation of the tribological behavior of EB-PBF Ti-6Al-4V, focusing on the effects of intra-build variability (orientation, height, radial location) and powder reuse. To address these, this dissertation presents a holistic study of tribological response of EB-PBF Ti-6Al-4V through sliding wear tests and erosion wear tests. The sliding wear tests included a ball-on-disc test against steel counterpart according to ASTM G99, rotary abrasion test against ceramic abrasive particle according to ASTM F1978, and a brief scratch test against steel ball. The erosive (erosion) wear test was conducted against silica and alumina particles according to ASTM G76. Wear tests were conducted in both as-built and machined surface conditions. Key tribological metrics such as specific wear rate, friction coefficient, erosion resistance, and wear depth were quantified through sliding wear and erosion tests. Surface roughness, microstructure, and sub-surface microhardness were characterized by understanding the wear mechanisms under varying conditions. In the as-built conditions, the specific wear rate is 7.63-8.74 × 10^(-3) mm^3/Nm against silicon carbide and 5.44-6.25 × 10^(-3) mm^3/Nm against alumina using 12.5 mm wide abrasive strip in the rotary abrasion test under 19.62 N load. In the machined condition, such values are 7.51-8.18 ×10^(-3) mm^3/Nm against silicon carbide and 4.96-5.54 ×10^(-3) mm^3/Nm against alumina. The specific wear rate ranges from 3.8 × 10⁻⁴ to 8.8 × 10⁻⁴ mm³/Nm against steel (9.5 mm diameter) in ball-on-disc test under 10 N load in machined conditions, while the average rate is 5.8 × 10^(-4) mm^3/Nm for all orientations. The wear rate is higher in the rotary abrasion test compared to the ball-on-disc test due to larger contact area. The friction coefficient range is 0.32-0.40 and 0.26-0.45, respectively for as-built and machined conditions. As-built specimens show orientation-dependent wear and frictional behavior, primarily influenced by surface roughness and microstructural anisotropy. Machining significantly reduces this variability, leading to more uniform wear response. Erosion tests indicate ductile erosion mechanisms dominated by micro-cutting and ploughing, with the angle of particle impingement and abrasive type (e.g., alumina vs. silica) significantly affecting material loss. The numerical erosion resistance of EB-PBF Ti-6Al-4V against silica is 1.49-1.84 × 10^(-4) mg/mg, and against alumina is 3.24×10^(-4) mg/mg in as-built and 5.51×10^(-4) mg/mg in machined conditions. Powder reuse increases surface hardness due to elevated oxygen content and lower abrasive wear rate. Tribological properties are sensitive to build orientation and surface condition. This dissertation also explores microstructural evolution and the variation of microhardness and microstructure with thickness. The machinability of EB-PBF Ti-6Al-4V has been assessed, and optimal face milling parameters are proposed to remove surface asperities while minimizing cutting forces and improving surface finish. The cutting coefficient of EB-PBF Ti-6Al-4V is 2016.29 N/mm^2. This dissertation presents a holistic framework to understand the tribological behavior of EB-PBF Ti-6Al-4V, contributing critical insights for its reliable use in wear-critical applications and supporting broader industrial adoption.application/pdfen-USnoneAdditive manufacturingElectron beam powder bed fusionTi6Al4VTitaniumTribologyMechanical engineeringMaterials ScienceMechanical engineeringThesis