Oxidation Kinetics of Ti-6Al-4V Alloys by Conventional and Electron Beam Additive Manufacturing

Abstract

New manufacturing processes for metal parts such as additive manufacturing (AM) provide a technological development for the aeronautical and aerospace industries, since these AM processes are a means to reduce the weight of the parts, which generate cost savings. AM techniques such as Laser Powder Bed Fusions (LPBF) and Electron Beam Fusion (EBM), provided an improvement in mechanical properties, corrosion resistance, and thermal stability at temperatures below 400 °C, in comparison to conventional methods. This research aimed to study the oxidation kinetics of Ti-6Al-4V alloys by conventional and Electron Beam Additive Manufacturing. The thermogravimetric analysis was performed at temperatures of 600 °C, 800 °C, and 900 °C, having a heating rate of 25 °C/min and oxidation time of 24 h. The microstructural analysis was carried out by thermogravimetric analysis. Thickness and morphology of oxide layers were analyzed by field emission scanning electron microscope, phase identification (before and after the oxidation process) was realized by X-ray diffraction at room temperature and hardness measurements were made in cross section. Results indicated that the oxidation kinetics of Ti-6Al-4V alloys fabricated by EBM was similar to conventional processing and obeyed a parabolic or quasi-parabolic kinetics. The samples oxidized at 600 °C for 24 h presented the lowest hardness values (from 350 to 470 HV). At oxidation temperatures of 800 and 900 °C, however, highest hardness values (from 870 close to the alpha-case interface up to 300 HV in base metal) were found on the surface and gradually decreased towards the center of the base alloy. This may be explained by different microstructures presented in the manufacturing processes.

High Temperature Oxidation Behavior of Additive Manufactured Ti6Al4V Alloy with the Addition of Yttrium Oxide Nanoparticles

“…However, the surface microhardness value of the Ti6Al4V-1.0 wt.% Y 2 O 3 alloy increases until 800 °C and then decreases at 1000 °C, which can be explained by the competition mechanism. The change in microhardness is mainly attributed to the heterogeneity quality and the oxide surface layer hardening occurring [ 7 ], which is also affected by the increase in the oxidation temperature and the diffusion of oxygen from the outside of the oxide layer [ 32 ].…”

Ceramic Conversion Treatment of Commercial Pure Titanium with a Pre-Deposited Vanadium Layer

“…Therefore, oxygen diffusing inwards dominates the growth of the oxide layer, which is also affected by the dense layer causing a slow oxidation rate [18]. For traditional oxidation, it is relatively fast before the oxide layer forms at the beginning, and then thermal oxidation slows down, as atoms need to diffuse through the oxide layer (Figures 4 and 7) [19,20].…”

Corrosion Resistance of Titanium Alloys Anodized in Alkaline Solutions

“…The authors reported that the passive layer is homogenous when passivate is generated in pure titanium (Ti CP2 or any CP). However, when the passivation is created in titanium alloy, the passive layer can be heterogeneous due to the difference in alloying elements; adding a small oxide layer can be a problem due to the penetration of different ions (Cl − , OH − or SO 2 2− ) in the surface by interstitial mechanisms [16][17][18][19][20]. Other options to protect titanium are plasma electrolytic oxidation (PEO) and sol-gel coatings; those techniques require special equipment to generate the layer, and the cost and difficulty of coating increase in some geometries [21,22].…”