Influence of Powder Heat Treatment on the Microstructure and Mechanical Properties of Cold Sprayed Ti-6Al-4V Coatings

Ti-6Al-4V is widely used in the aerospace industry, however, Ti-6Al-4V repairs are challenging to perform via cold spray due to the material’s limited capacity for plastic deformation. To promote particle deformation, this study investigated the influence of Ti-6Al-4V powder heat treatment on the powder microstructure, cold spray deposition behavior, and, ultimately, on the coating microstructure and properties. Plasma-atomized Ti-6Al-4V powder was subjected to three different heat treatments (i.e., 540 °C for 5 h, 750 °C for 2 h, and 950 °C for 2.5 h) and subsequently deposited on Ti-6Al-4V substrates using a high-pressure cold spray system. Scanning electron microscopy revealed that the as-received microstructure was primarily characterized by a martensitic alpha microstructure. After low-temperature heat treatment (540 °C), the microstructure retained the original martensitic alpha microstructure. Intermediate heat treatment (750 °C) resulted in the formation of needle-like alpha and acicular alpha with fine beta precipitates. High-temperature treatment (950 °C) resulted in the formation of needle-like alpha, acicular alpha, and plate-like alpha with coarse and fine beta precipitates. The hardness of the powder increased after heat treating at 550 °C and 750 °C but decreased when treated at 950 °C. After cold spray deposition, particle interiors retained the as-processed powder microstructure while regions near particle boundaries exhibited either a featureless microstructure (as-received powder and low-temperature heat treatment) or elongated β (high-temperature heat treatment). With the exception of 750 °C powder heat treatment, all coatings were nearly dense (< 1% porosity). Ultimately the results showed that 950 °C heat treatments have the potential to improve powder deformation behavior and coating properties.