Corrosion behavior and mechanism of laser powder bed fusion produced Ti-Cu alloys

Author Identifier


Date of Award


Document Type

Thesis - ECU Access Only


Edith Cowan University

Degree Name

Master of Engineering Science


School of Engineering

First Supervisor

Lai-Chang Zhang

Second Supervisor

Hongqi Sun


The Laser Powder Bed Fusion (LPBF) process, a subset of Additive Manufacturing (AM), has recently gained considerable traction in metal production, especially for fabricating complex and near net-shaped parts. This innovative process has been shown to be advantageous in many fields. For example, this process is particularly beneficial for biomedical applications, where the production of implants requires specific shapes to accommodate diverse bone tissues. Unlike traditional manufacturing methods, which primarily involve the removal of material from an ingot, LPBF offers significantly reduced production cycles and maximized material utilization.

Mechanical properties of alloys produced through the LPBF process have been shown to be either superior or comparable to those produced through conventional methods. This enhancement could be attributed to the rapid cooling rate that is inherent in the LPBF process. However, some LPBF-produced alloys can present worsened corrosion resistance, especially when exposed to harsh environments (e.g., marine). Therefore, this thesis provides a comprehensive study of corrosion-related aspects of LPBF-produced Ti alloys and explores the benefits of copper (Cu) as an additive element into Ti. Cu is known for its corrosion resistance and antibacterial properties, which make it particularly beneficial in biomedical and marine environments, respectively.

To fulfill the requirements for biomedical applications, the corrosion behaviors of as-LPBF-produced Ti5Cu (named as LPBFed) and as-LPBF-produced Ti5Cu after 740 °C and 900 °C heat treatments (named as HT740 and HT900 respectively) were investigated by electrochemical and surface characterization methods. The heat treatment provides an effective post treatment method for the LPBF method to remove residual stress and eliminate the non-equilibrium phase in the produced Ti alloys. The results indicate that heat treatment enhances the corrosion resistance of LPBFed Ti5Cu. In HT740 and HT900, their increased volume fraction of the Ti2Cu phase presents in the microstructure could further enhance the corrosion resistance with a larger thickness of the oxide film than LPBFed Ti5Cu, and the Ti2Cu phase provides an ‘envelope’ effect to slow down the micro-galvanic reaction between the a'/a-Ti and Ti2Cu phase.

In addition, this work also investigates the corrosion behavior and mechanism of those three LPBF-produced Ti5Cu (LPBFed, HT740 and HT900) in acidic (pH=2) NaCl solution (3.5 wt%). The results indicate that heat treated Ti5Cu provides better resistance to corrosion by forming a stable oxide film with a lower electron diffusion rate on the surface. Furthermore, the existence of the Ti2Cu phase in the heat-treated samples acts as a micro-anode that decelerates corrosion on the a-Ti phase, whereby a long-term immersion test also confirms Cu ion release on both HT740 and HT900 to be higher than that in the LPBFed Ti5Cu (prior dissolution of Ti2Cu phase). The reason for the worsened corrosion resistance of the LPBFed Ti5Cu is that the acidic environment (e.g., Cl-) accelerates the electron diffusion rate in the film/solution interface, which in turn makes the thermodynamically unstable phase of a'-Ti being preferential corrode when compared with heat-treated counterparts.

In addition, the as-LPBF-produced Ti7Cu was also investigated under different NaCl solutions with the concentration of 0.9, 3.5 and 10 wt% to investigate the effects of Cl ions on the LPBF-produced Ti-Cu alloy. The electrochemical test results proved that the increase in NaCl concentration can strongly affect the corrosion resistance of Ti7Cu. However, the specific corrosion mechanism still needs to be investigated and analyzed in further work.

In this thesis, the corrosion mechanism of LPBF-produced Ti5Cu and Ti7Cu has been explored, and the results provide further accumulation for the application of LPBFed Ti-Cu alloy in both simulated human body environment and different concentrations of NaCl environments.



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