Titanium has two crystalline forms with reversible transformation at 880 ° C. The α form is tetragonal and has d = 4.505 g / cm3 at a temperature of 25 ° C. The β form is cubic with a centered body and has d = 4.35 g / cm3 at a temperature of 25 ° C; melts at 1668 ° C.
The mechanical characteristics of titanium are as follows: breaking load 560 N / mm2; elastic limit 46 kg / mm2; elongation 25%; hardness 200-220 Brinell.
The modulus of elasticity is about twice that of 18-8 stainless steels, to which it can be compared for its corrosion resistance.
The solubility of oxygen is relevant: for oxygen, about 4% by weight in the β form and up to 33% in the α form.
Titanium passively spontaneously at room temperature or in contact with tissue fluids. The osseointegrative theory predicts that, thanks to electrostatic chemical forces, titanium oxide forms a close chemical bond with the metal.
The elements most commonly introduced in titanium-based alloys behave either as stabilizers of the α phase or as stabilizers in the β phase. Among the stabilizers of the α phase the most common is aluminum; the vanadium vice versa lowers the transformation temperature β → α.
Commercially pure titanium is classified into five grades (1, 2, 3, 4, 7) by the ASTM regulation.
The table on the following page compares the properties of the main construction metals
|point of fusion||1668||1530||1400-1420||660||1083|
|module of young||10850||21000||20400||6900||1100|
Tab. 6 – 1