Titanium

Titanium was a metal (PROSE: Venusian Lullaby) on the periodic table with the symbol Ti (TV: Shada) and an atomic number of 22. (PROSE: Iris Wildthyme y Señor Cientocinco contra Los Monstruos del Fiesta)

The vault of the bank on Centuria was made of titanium. (COMIC: Time of the Cybermen)

The metal used in Vondraxian orbs shared properties with titanium and zinc, but was neither. (PROSE: Trace Memory)

SERVEYOUinc used titanium vault-like doors to protect their most sensitive research at the United System Research Base. (COMIC: The Sound of Our Voices)

When Amy Pond agreed to be Laura's bridesmaid during an October day in the early 21st century, a song was playing at the party. It contained the lyrics "I am titanium / You shoot me down, but I won't fall / I am titanium". (TV: The Power of Three)