The material chosen for the experiments was full hard 301 stainless steel manufactured by H+S Folien https://hs-folien.de/en/home.html and distributed in the UK by Repco Technology ltd https://www.repco-tech.co.uk/ . There are a few materials that could result in higher tip speed fans.
High Carbon Steel.
High Carbon steel (1.1274) has a higher endurance limit compared to 301 Stainless, but it oxides readily in indoor conditions. Oxidation produces imperfections that can initiate crack development and ultimately failure of the fan. If high carbon steel is chosen, oxidation mitigation coating would have to be employed. This would be tricky at the fan clamping position, due to the high stresses. Titanium alloys have the potential to produce a faster fan blade.
Titanium
Titanium alloys have a lower young’s modulus than steel. The tip speed equation presented in the paper show that a lower young’s modulus results in a higher tip speed. The problem is that to achieve a high strength titanium alloy, it needs a full hard temper. Titanium alloys have a more complicated tempering process compared to steel. Titanium can’t be cold rolled, so need to be heat treated. Heat treating titanium sheets are very likely to warp. Also, I understand that after heat treating titanium, surface layers have to be removed in order to maintain high performance. If these manufacturing issues can be overcome, the fan blade would have impressive performance. I did test a sheet of untempered Ti6Al4V. At 1.5mm thick and 24cm long, it had a maximum tip speed of 16 m/s. Witnesses this fan, I realized that it was quite a unique experience seeing such a powerful (and potentially dangerous fan). As the sheet was not tempered, it failed in less than 24 hours.
Glass fiber composite.
I did not experiment with this material, as I incorrectly assumed that it does not have an endurance limit.