Investigating the feasibility to remove alpha case from titanium alloys with machining
CITATION: Conradie, F. W., Oosthuizen, G. A. & Sacks, N. 2016. Investigating the feasibility to remove alpha case from titanium alloys with machining. In Competitive Manufacturing, International Conference on Competitive Manufacturing (COMA '16), 27-29 January 2016, Stellenbosch, Stellenbosch University, South Africa.
The original publication is available at http://conferences.sun.ac.za/index.php/doie/coma16
Titanium as an alloy offers excellent material properties including corrosion resistance, biocompatibility and high specific strength. These properties make titanium alloys highly desirable in demanding applications and specialised industries such as aerospace and orthopaedic prosthesis. However, the formation of a hard and brittle alpha case layer at elevated temperatures requires hot forming processes to be conducted either in inert atmosphere, or vacuum. Alternatively, alpha case could be removed post process by chemical milling which requires high capital costs as well as stringent safety measures. Alternative removal techniques are therefore under investigation and one such option is machining removal which can make use of the already established South African machining industry. Excessive wear due to the hardened alpha case layer results in machining removal not currently being viewed as economically feasible. This investigation therefore focusses on identifying possible machining guidelines for the removal of alpha case from titanium alloys. Thereafter, a comparison is made between machining removal of alpha case with chemical milling in the context of the South African manufacturing industry. It was observed that alpha case is readily removed at all machining conditions and that excessive notching and accelerated wear rates are experienced at high cutting speeds. Wear rates more commonly attributed with titanium machining is observed at lower cutting speeds.