Removal of alpha case on titanium alloy surfaces using chemical milling

Elevated temperature deformation processing of titanium such as during forging causes the formation of alpha case, a brittle layer on the processed components. Alpha case removal has been attempted by several methods, however, in-depth understanding of chemical milling to this end is not evident from the prevailing literature. This work therefore undertakes experimental analysis of chemical milling to remove alpha case generated on titanium alloys after deformation after forging. Several compositions of chemicals and heat treatment conditions for titanium work-material were evolved. Effectiveness of these methods and their applications in removing alpha case on forged titanium alloy were investigated by performing a series of experiments. After the alpha case removal, the titanium work surfaces were examined using optical and scanning electron microscopy as well as electron back scattered diffraction and X-ray diffraction. The optimum results achieved show that 8% HF and 10% HNO₃ solution with 13 min and 30-s etching time is more effective in completely removing alpha case layer by chemical etching of Ti-6Al-4V alloy work specimens heated in air at 930°C.