High-Temperature Corrosion of Ti6Al4V and In-situ Reinforced Composites Fabricated by Laser Additive Manufacturing

This study investigates the high-temperature corrosion behaviour of Ti6Al4V (Ti64) alloy and its composites, TiC/Ti64 and in-situ TiBw/Ti64, fabricated using directed energy deposition. Corrosion tests were performed at 300°C, 600°C, and 900°C in oxygen-rich NaCl–Na₂SO₄ environments. Thermogravimetric analysis showed in-situ TiBw/Ti64 had the highest resistance due to stable boron oxides maintaining protective layer integrity. TiC/Ti64 displayed intermediate resistance, with instability of oxide layers at higher temperatures. Ti64 suffered severe material loss from volatile titanium chlorides and sulphates disrupting oxide scales. Microstructural characterization by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) revealed critical insights into phase distribution and stability. TiC and TiB reinforcements influenced grain boundary stabilization, phase distribution, and oxide adherence. TiC acted as a barrier to defect growth and oxygen diffusion, improving oxide protection. TiB enhanced resistance through boron oxides and high thermal stability, though galvanic interactions posed challenges. Both composites offered significant improvements over Ti64 for aerospace, marine, and power generation applications exposed to saline and high-temperature environments, especially below 600°C. In-situ TiBw/Ti64 proved most effective at elevated temperatures due to excellent thermal stability and resistance to oxide spallation. TiC/Ti64, while performing well, showed limitations at high temperatures, requiring further optimization. These findings highlight the importance of composite microstructures in tailoring titanium alloys for harsh environments, with in-situ TiBw/Ti64 particularly suitable for high-temperature service.