High-temperature corrosion of Ti6Al4V and in-situ reinforced composites fabricated by laser additive manufacturing

Abstract

This study investigates the high-temperature corrosion behaviour of directed energy deposited (DED) Ti6Al4V (Ti64) and its in-situ composites (TiC/Ti64 and TiBw/Ti64) in oxygen-rich NaCl- Na 2 SO 4 environments at 300 °C, 600 °C, and 900 °C. DED produces refined microstructures with reinforcement phases distributed along grain boundaries, fundamentally altering corrosion mechanisms. Thermogravimetric analysis revealed that TiBw/Ti64 exhibited superior resistance (activation energy: 282 kJ/mol) due to the formation of stable boron oxides (B2O3) that maintained protective layer integrity through self-healing mechanisms. TiC/Ti64 showed intermediate performance (276 kJ/mol), with TiC particles acting as oxygen diffusion barriers but undergoing oxidation at > 800 °C to form TiO2 and carbon residues. Unreinforced Ti64 suffered severe material loss (198 kJ/mol) via volatile TiCl4 formation that disrupted the oxide scale. Microstructural analysis demonstrated that AM-induced grain refinement enhanced oxide nucleation site density, while reinforcement distribution influenced galvanic interactions. These findings establish that in- situ TiBw/Ti64 fabricated by DED offers optimal performance for aerospace and marine. applications below 600 °C, with degradation mechanisms transitioning from surface oxidation to bulk volatilization above this threshold.