Investigation of hot-dip aluminized Ti6Al4V alloy processed by different thermal treatments in an oxidizing atmosphere

Plasma assisted aluminide coating was formed on Ti6Al4V alloy by hot-dip aluminizing (HDA) followed by two-step diffusion heat treatment. The HDA coated Ti6Al4V alloys were subjected to solution annealing (900 degrees C/1 h) and aging heat treatment (500 degrees C/6 h) by plasma processing route and compared with thermal treatment. The resultant coated and heat-treated samples were characterized using SEM for surface morphology and microstructure analysis, EDS for elemental analysis and x-ray diffraction (XRD) for phase analysis. From the characterization, it was observed that after the diffusion heat treatments, the microstructure of aluminized coating consisted of an outer layer of Al2O3 followed by TiAl3, TiAl2, Ti-Al, and Ti3Al phases. In the diffusion zone, hardness variation in the range of 366-490 HV0.05 and 342-525 HV0.05 was observed in case of thermal and plasma-treated samples respectively. However, in the diffusion zone, the microhardness of plasma-treated samples was slightly higher than the thermally treated samples. The plasma ion bombardment appears to alter the crystalline size due to vacancy concentration which leads to increment in the hardness value. The details of experiments, characterization along with the interpretations and comparison of various microstructural aspects have been presented in this manuscript.