Evaluation of Ti-6Al-4V Parts Produced with Rapid Prototyping Technology: Electron Beam Melting Machine

The present study measured the corrosion properties of Ti-6Al-4V parts produced with Electron Beam Melting machine (EBM). Potentiodynamic and potentiostatic tests were applied on EBM Ti-6Al-4V in 3.5% mass NaCl solution, to determine the pitting potential and critical pitting temperature (CPT). A relation between pitting potential and temperature was established for EBM Ti-6Al-4V alloy by conducting potentiodynamic test under different temperatures from room temperature until 83?C. Critical pitting temperature was also measured in 3.5% mass NaCl solution of different pH of 2.0, 5.7 and 10.0, to examine the effect of aggressive conditions on the pitting corrosion of EBM alloy. Moreover, the same tests were performed on wrought Ti-6Al-4V for comparison purposes. The results showed that EBM alloy maintained its corrosion resistance as it had the same pitting potential of wrought alloy even at higher temperatures. EBM alloy did not pit when performing potentiostatic test at 800 mV vs. Saturated Calomel Electrode (SCE) even under different pH of the solution.

Due to the manufacturing technique and conditions of the EBM machine, the resulted object has irregularities on the exterior surface and voids that are formed within the part which affects samples? properties like surface roughness, CPT, density and porosity. In this study, a statistically designed experiment was employed to manufacture Ti-6Al-4V samples in EBM machine under different process parameters of beam current, beam speed and offset focus. Surface roughness was measured for as-built samples. Then, a potentiostatic test was conducted under 2.40 V vs. SCE to determine the critical pitting temperature in 3.5 % mass NaCl solution for the same samples of different processing parameters. Moreover, density was measured and porosity was calculated from density values. Finally, a model equation was established in order to relate EBM?s process parameters to measured properties of surface roughness, CPT, density and porosity. It was noted that offset focus had the main influence on surface roughness more than beam current and beam speed. Changing processing parameters did not affect corrosion behavior of EBM Ti-6Al-4V as CPT did not vary widely, with a slight effect obtained from beam current and beam speed. Density and porosity were greatly affected with offset focus more than the other parameters. It can be concluded that uniform and precise roughness and porosity are not achievable through this machine, only a range of these properties can be attained.