Corrosion Behavior of Nano/Sub‐Micron F401 Titanium Alloy

Abstract

Titanium alloys are attractive as structural materials mainly due to their high specific strength and excellent corrosion resistance. Modifying conventional Ti alloys to impart nanostructural features holds promise for improving specific strength without reducing corrosion resistance. This study aimed to evaluate the corrosion behavior of a nano/sub-micron F401 titanium alloy compared to its conventional Ti-6Al-4V counterpart. Following mechanical alloying and extrusion, the microstructure was evaluated using optical microscopy, SEM, HRSEM, and X-ray diffraction analysis. Mechanical properties were evaluated by tension and micro-hardness tests. The corrosion behavior was examined by an immersion test, salt spray testing, and potentiodynamic polarization analysis. Stress corrosion resistance was evaluated by slow strain rate testing (SSRT) in terms of UTS and time to failure versus strain rate. All the corrosion tests were carried out in 3.5% NaCl solution apart from the salt spray testing, which was done in 5% NaCl solution. The results indicate that the corrosion resistance of the novel F401 alloy was not different from its Ti-6Al-4V counterpart, although the mechanical strength was improved. Thus, the grain refinement in the F401 alloy increased the mechanical strength, whereas neither the grain refinement nor the porosity acquired during the preparation process impaired the excellent corrosion resistance.

Corrosion Degradation Behaviors of Ti6Al4V Alloys in Simulated Marine Environments

“…These diffraction peaks of sample H1 are mainly attributed to the initial α-Ti and (α + β)-Ti phases. It has been reported that a passivation film consisting mainly of TiO 2 forms on the surface of the titanium alloy during the salt spray exposure [20,25]. As shown in Figure 5c, the Ti2p 3/2 and Ti2p 1/2 peaks in sample H1 locate at 458.48 and 464.17 eV, respectively, which correspond to the Ti-O binding state, confirming the formation of a thin TiO 2 passivation film [26].…”

“…Obviously, the Cl 2 acts as a key carrier, accelerating the degradation reaction of the substrate, and results in the rapid growth of the oxide layer. As identified by the SEM image of Figure 8c, the continuous volatilization of chloride and the significant structure differences of these oxides trigger high thermomechanical growth stress, which eventually results in a severe layered separation and local cracking [36] since the coefficients of thermal expansion of TiO 2 , Al 2 O 3 , and Ti6Al4V alloy are 8.2 × 10 −6 , 8.1 × 10 −6 , and 10~12 × 10 −6 K −1 , respectively [25]. Therefore, the significant difference in thermal expansion coefficients between the oxide layer and substrate eventually induces the initiation of surface ring breaking [37].…”

High Entropy Alloys: Prospective Materials for Tribo‐Corrosion Applications

“…Degradation behavior of a wide range of materials has been investigated . Stainless steels are often used as structural material in the corrosive environment due to their ability to form stable passive layer .…”