Polishing Titanium Metal – How and Why
Titanium is extremely lightweight and strong, but its high ductility also makes it prone to mechanical deformation throughout the fabrication process. This means that proper polishing is very important to ensure a smooth, shiny surface that remains resistant to corrosion. Without this step, titanium metal and alloys will have a very scratchy appearance and potentially experience unwanted problems.
There are a number of techniques that can be used to clean and polish titanium in order to create that smooth, shiny surface that is free of deformations. The most common methods involve chemical and mechanical polishing, but there are also options for an electrochemical (or electrolytic polishing) method that can speed up the entire process.
Chemical / Mechanical Polishing
Chemical polishing normally requires some kind of hydrofluoric acid reagent to fully treat the surface of the titanium. The chemical alone is a good way to clean the surface, but it doesn’t necessarily smooth or level it the way other methods do. In some cases, though, an HF reagent may be seen as too corrosive, so the chemical treatment is combined with a mechanical polishing process.
It is possible to use something less corrosive, like hydrogen peroxide, and mix it with colloidal silica to mechanically produce effective results. This process can create a very smooth and flat surface (as well as nice and shiny) but it is also more time-intensive and can require more work to produce the necessary results. There is also a chance that this method will leave polishing media on the surface, but as long as the proper precautions are taken (with both chemical and mechanical polishing), it is possible to consistently get the results you need.
Electrolytic (or electrochemical) polishing can remove unwanted materials from the surface of titanium materials and leave a fine, polished finish. The process works by placing the metal in an electrolyte bath, which can include perchloric acid, methanol, and butanol, and then sending a specified voltage through it. The result is a faster, reliable polishing process.
Electrolytic polishing can be used on titanium that has already been fabricated into different shapes, because it simply needs to fit into the electrolyte bath to work. This process can also effectively level out any peaks because the chemical layer on the high points is more concentrated that the depressions, causing them to dissolve much faster.
A Note on Anodizing
There is also a thermal treatment that can help create a smooth, resistant surface on titanium as well, but the process is a little different. Anodizing requires an extremely clean piece of titanium to begin with, and by applying intense levels of heat the thickness of the surface oxide can increase, which will have an effect on the corrosion resistance. While it’s possible to change the color of titanium this way, it is not actually “polishing” the metal.
Why Does It Matter?
When everything is done correctly, the final result should be titanium metal that looks white under an optical microscope. If it doesn’t, the polishing process will have to continue. So the question is whether or not it’s really worth the trouble.
A smooth, polished titanium surface will make it easier to clean and the better profile will lower the water contact angle, improving the corrosion resistance. Polishing isn’t just about making products nice and shiny – it’s about ensuring a high level of quality on every piece of titanium.