Titanium Surface Properties: A comparison of titanium from two suppliers

Abstract: This master thesis, completed at the company Alfa Laval studied the surface properties of grade 1 titanium from two different suppliers to examine if there were any significant differences between the two suppliers. Previously titanium from the two suppliers had performed differently at times when used in Alfa Lavals heat exchangers. The experiments performed where studies of surface energy, surface roughness, corrosion rates, Vickers hardness, surface chemistry using GD-OES, grain size and crystal direction using EBSD and tensile tests. Both titanium in sheet form and titanium that had been pressed into heat exchanger plates was tested. The results showed that there were some differences between the suppliers. Supplier 1 had a smaller grain size, slightly higher surface energy and was softer. But the most remarkable difference was in corrosion rate. Supplier 1 titanium corroded as expected but Supplier 2 titanium barely corroded at all and became colored. The probable reason for this is that Supplier 2 has a higher carbon contentment in its surface thanks to differences in the production process between suppliers. This carbon causes the oxide layer of the titanium to grow in the corrosion tests instead of disappearing. This increased thickness of the oxide layer is what is what causes the color change. Note that this is only a theory and not verified in this report.