Page 47 - PCMI Journal July 2018
P. 47
David Allen | Emeritus Professor | Cranfield University | UK Photochemical Machining of Aerospace Materials
5/31/18
PCM with HF solutions as etchants
Etchants containing HF can be utilised to etch a wide variety of difficult-to-etch metals and alloys such as:
• Columbium (Niobium)
• Titanium and titanium aerospace alloys such as Ti-6Al-4V
• Zirconium
• Nickel-Titanium (Nitinol) Shape Memory Alloys
HF in Chemical Milling
• Titanium is one of the most important aerospace materials, being light, strong and corrosion resistant.
• Titanium and its alloys are usually chemically milled in HF solutions according to the equation;
Ti (s) + 3HF (aq) → TiF3 (s) + 3/2H2 (g)
TiF3 (s) + 6H2O → TiO2.4H2O (s) + 3HF (aq) + 1/2H2 (g) leading to the overall reaction:
Ti (s) + 6H2O → TiO2.4H2O (s) + 2H2 (g)
Nitric acid is therefore added to prevent hydrogen embrittlement
Issue 131 July 2018 PCMI Journal 46
3
