• Microstructure changes greatly affect the corrosion behavior of β titanium alloy. • Less α-phase precipitation improves the alloy's corrosion resistance in HCl solution. • Element enrichment causes micro-galvanic couple effects in alloys. • More phase interfaces contribute to the formation of a stable passive film. The corrosion behavior of Ti-4Al-6Mo-2V-5Cr-2Zr alloy with a forged microstructure, hierarchical nanostructure (HN), and lamellar microstructure (LM) in a 5 mol/L HCl solution has been studied. The HN alloy comprises micron-sized primary α phase ( α p ), grain boundary α phase (GB α ), and nanoscale secondary α phase ( α s ), with an α phase volume fraction of 37.2%, the LM alloy formed by needle-like α s , with an α phase volume fraction of 28.5%, and a forged microstructure predominantly featuring an equiaxed β phase, with an α phase volume fraction of 4.7%. Electrochemical test results indicate that the forged alloy exhibits the best corrosion resistance in 5 mol/L HCl solution, characterized by the lowest corrosion current density of 4.677 µA/cm², a corrosion rate of 0.126 mm/a, and the thickest passive film measuring 5.46 nm. Key factors affecting the corrosion performance of the alloys include the uniformity of alloy element distribution and the characteristics of the α phase. The forged alloys demonstrate minimal segregation of elements, which effectively mitigates micro-galvanic couple effects. However, in LM and HN alloys, the enrichment of Al and the absence of Mo and Cr in the α phase lead to the formation of micro-galvanic couple effects between the precipitated phase and the β matrix, resulting in preferential corrosion of the α phase. Additionally, a thicker α phase in the microstructure, along with a higher volume fraction, correlates with poorer corrosion resistance of the alloy.
Wang et al. (Sun,) studied this question.