The difference between titanium and titanium alloy screws

Titanium is a chemical element, chemical symbol Ti, atomic number 22, in the periodic table of chemical elements in the fourth period, the IVB group. It is a silver-white transition metal characterized by light weight, high strength, metallic luster and resistance to wet chlorine corrosion. But titanium can not be used in dry chlorine gas, even if the temperature is below 0℃ dry chlorine gas, will also take place drastic chemical reaction, generate titanium tetrachloride, and then decompose to generate titanium dichloride, and even combustion. Only when the water content of chlorine is above 0.5% can titanium remain reliably stable in it. [1]

Titanium is considered a rare metal because it is dispersed in nature and difficult to extract. But it is relatively abundant, ranking tenth among all the elements.

Titanium ores mainly include ilmenite and rutile, widely distributed in the Earth's crust and lithosphere. Titanium is also found in almost all living things, rocks, water and soil. The extraction of titanium from the main ore is done by the Croyle process

Or Hunter's method. The most common compound of titanium is titanium dioxide, which is used to make white pigments. Other compounds include titanium tetrachloride (TiCl4) (used as a catalyst and as air cover for smoke screens) and titanium trichloride (TiCl3) (used as a catalyst for the production of polypropylene).

Titanium alloy is an alloy based on titanium with other elements. There are two kinds of homogeneous heterocrystals of titanium: α-titanium with dense hexagonal structure below 882℃ and β-titanium with body-centered cubic structure above 882℃.

Alloying elements can be divided into three categories according to their influence on the phase transition temperature:

① The elements that stabilize α phase and increase phase transition temperature are α stable elements, such as aluminum, carbon, oxygen and nitrogen. Aluminum is the main alloy element of titanium alloy, which has obvious effects on improving the strength of alloy at room temperature and high temperature, reducing the specific gravity and increasing the elastic modulus.

(2) The elements that stabilize the β phase and reduce the temperature of the phase transition are β stable elements, which can be divided into two types: homomorphic type and eutectic type. The former has molybdenum, niobium, vanadium, etc.; The latter have chromium, manganese, copper, iron, silicon and so on.

(3) The elements that have little effect on the phase transition temperature are neutral elements, such as zirconium and tin.

Oxygen, nitrogen, carbon and hydrogen are the main impurities in titanium alloys. Oxygen and nitrogen have greater solubility in the α phase, which can strengthen the titanium alloy significantly, but decrease the plasticity. The content of oxygen and nitrogen in titanium is usually set below 0.15 ~ 0.2% and 0.04 ~ 0.05%, respectively. The solubility of hydrogen in the α phase is very small, and too much hydrogen dissolved in titanium alloy will produce hydrides, which will make the alloy brittle. The hydrogen content of titanium alloys is usually limited to

Less than 0.015%. The dissolution of hydrogen in titanium is reversible and can be removed by vacuum annealing.

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