MATERIALS
On the structural characterization of thermo-reactive diffusion coated cast Ti6Al4V alloy
Abstract: Thermo-reactive diffusion (TRD) coatings are formed on conventionally cast Ti6Al4V alloy using the pack cementation process to improve its surface characteristics. Aluminizing, siliconizing, and molybdenizing treatments are carried out at 700 °C, 1000 °C, and 900 °C, respectively, for 2 h using Al, Si, and Mo powder packs containing NH₄Cl as the activator and Al₂O₃ as the inert filler. The resulting coatings are systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) to investigate phase evolution, coating morphology, and elemental distribution. XRD analyses confirmed the formation of Ti–Al intermetallics (TiAl, TiAl₂, TiAl₃), Ti–Si silicides (TiSi, TiSi₂, Ti₅Si₃), and Mo-enriched Ti solid-solution phases within the coatings. Cross-sectional SEM observations have revealed continuous and well-adhered diffusion layers with thicknesses of approximately 20 μm for the aluminized coating and 50 μm for the molybdenized coating, while the siliconized layer (40 μm) exhibits a graded multilayer silicide structure. EDS elemental mappings have demonstrated inward diffusion of the deposited species and outward diffusion of substrate elements, confirming diffusion-controlled coating growth. The formation of metallurgically bonded reaction layers with compositional gradients is expected to substantially enhance the surface hardness, wear resistance, and high-temperature performance of the Ti6Al4V alloy. The results demonstrate that thermo-reactive diffusion by pack cementation provides an effective and controllable route for tailoring the surface microstructure of cast Ti6Al4V through appropriate selection of coating chemistry and processing conditions.