Optimization of the chemical milling of investment cast titanium alloys

Investment casting is a popular casting technique for manufacturing of several titanium alloy components dedicated to different industrial applications, as aerospace and automotive. This manufacturing process could be an economic net-shape technology, since the investment casting allows obtaining complex shapes, accurate geometries and reduced thicknesses. However, the reactions between titanium in liquid state and ceramic shell result in the formation of the so called alpha case, a brittle layer developed by the interstitial elements such as carbon, nitrogen and especially oxygen dissolved from mold materials. The alpha case layer will deteriorate the surface of titanium castings, but it can be eliminated using chemical milling processes. This paper describes the work developed by the authors to investigate the effects of chemical milling on two of the most used titanium alloys: Ti6Al4V and CP Ti grade 2. The aim of this study is finding a reliable industrial method for performing chemical milling on titanium casting which can be efficient in terms of metal removal rate, repeatable and environmentally safe.