Investigation of the Chemical Machining for Removing of the Alpha-Case Due to the Hot Forging of Ti-6Al-4V Aerofoil

In this paper chemical machining of an aerofoil of a forged Ti-6Al-4V titanium alloy turbine blade has been investigated. First, the blade has been hot forged and then the metallurgical structure has been investigated. Using the microstructure and hardness measuring, surface alpha case has been investigated. Next, the chemical machining has been studied for removing of the alpha case. Hydrofluoric-nitric acid solution has been used for the chemical machining. Results show that the alpha case thickness on the forged aerofoil is considerable and the used chemical solution can remove it perfectly. Machining from the aerofoil surface is uniform and material removal rate increases as the temperature increases. During the chemical machining, first because of exothermic reaction, material removal rate increases, then it decreases because of decreasing the density of the acids.