Corrosion Science and Technology

The Corrosion Science Society of Korea (한국부식방식학회)
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Effect of Manufacturing Process on Electrochemical Properties of CP-Ti and Ti-6Al-4V Alloys

CP-Ti 및 Ti-6Al-4V 합금의 전기화학적 특성에 미치는 제조공정의 영향

  • Kim, K.T. (The Corrosion Science Society of Korea) ;
  • Cho, H.W. (The Corrosion Science Society of Korea) ;
  • Chang, H.Y. (The Corrosion Science Society of Korea) ;
  • Kim, Y.S. (The Corrosion Science Society of Korea)
  • Received : 2018.01.15
  • Accepted : 2018.02.12
  • Published : 2018.02.28
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Abstract

Ti and its alloys show the excellent corrosion resistance to chloride environments, but they show less corrosion resistance in HCl, $H_2SO_4$, NaOH, $H_3PO_4$, and especially HF environments at high temperature and concentration. In this study, we used the commercially pure titanium and Ti-6Al-4V alloy, and evaluated the effect of the manufacturing process on the electrochemical properties. We used commercial products of rolled and forged materials, and made additive manufactured materials by DMT (Directed Metal Tooling) method. We annealed each specimen at $760^{\circ}C$ for one hour and then air cooled. We performed anodic polarization test, AC impedance measurement, and Mott-Schottky plot to evaluate the electrochemical properties. Despite of the difference of its microstructure of CP-Ti and Ti-6Al-4V alloys by the manufacturing process, the anodic polarization behavior was similar in 20% sulfuric acid. However, the addition of 0.1% hydrofluoric acid degraded the electrochemical properties. Among three kinds of the manufacturing process, the electrochemical properties of additive manufactured CP-Ti, and Ti-6Al-4V alloys were the lowest. It is noted that the test materials showed a Warburg impedance in HF acid environments.

Keywords

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Fig. 1 Effect of heat treatment at 760 oC (1hr, air cooling) onthe anodic polarization behavior of CP-Ti made by various proc-ess in 50 oC 20% H2SO4; (a) CP-TiR (b) CP-TiF (c) CP-TiA.

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Fig. 2 Effect of heat treatment at 760 ℃(1hr, air cooling)on the anodic polarization behavior of Ti-6Al-4V alloys madeby various process in 50 oC 20% H2SO4; (a) Ti-64R (b) Ti-64F(c) Ti-64A.

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Fig. 3 Effect of manufacturing process on the anodic polarization behavior of CP-Ti and Ti-64 made by various process in 50 oC 20%H2SO4; (a) CP-Ti(R,F,A) as-received (b) CP-Ti(R,F,A) heat-treated (c) Ti-64(R,F,A) as-received (d) Ti-64(R,F,A) heat-treated.

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Fig. 4 Optical microstructure of (a, a’) cold-rolled CP-TiR, (b, b’) forged CP-TiF, and (c, c’) additive-manufactured CP-TiA.

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Fig. 5 Optical microstructure of (a, a’) cold-rolled Ti-64R, (b, b’) forged Ti-64F, and (c, c’) additive-manufactured Ti-64A.

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Fig. 6 Polarization behavior of CP-Ti and Ti-64 alloy made by various process in 20% H2SO4 + 0.1% HF (a) CP-Ti , (b) Ti-64.

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Fig. 7 Nyquist plot of CP-Ti and Ti-64 alloy made by various process at +1V(SCE) in 20% H2SO4 (+ 0.1% HF); (a) CP-Ti in 20%H2SO4 (b) CP-Ti in 20% H2SO4 + 0.1% HF (c) Ti-64 in 20% H2SO4 (d) Ti-64 in 20% H2SO4 + 0.1% HF.

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Fig. 8 Rp(polarization resistance) of (a) CP-Ti and (b) Ti-64 alloy made by various process at +1V(SCE) in 20% H2SO4 and 20%H2SO4 + 0.1% HF.

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Fig. 9 Mott-Schottky plot of CP-Ti and Ti-64 alloy made by various process at +1V(SCE) in 20% H2SO4 (+ 0.1% HF); (a) CP-Tiin 20% H2SO4, (b) CP-Ti in 20% H2SO4 + 0.1% HF, (c) Ti-64 in 20% H2SO4, (d) Ti-64 in 20% H2SO4 + 0.1% HF.

Table 1 Chemical composition of Ti-Gr.2 (wt%)

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Table 2 Chemical composition of Ti-Gr.5 (wt%)

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Table 3 Donor density of CP-Ti and Ti-64

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