Martensite, named after the German metallurgist Adolf Martens (1850–1914), is any crystal structure that is formed by displacive transformation, as opposed to much slower diffusive transformations. It includes a class of hard minerals occurring as lath- or plate-shaped crystal grains. When viewed in cross-section, the lenticular (lens-shaped) crystal grains appear acicular (needle-shaped), which is how they are sometimes incorrectly described. "Martensite" most commonly refers to a very hard constituent of steel (the alloy of iron and carbon) important in some tool steels. The martensite is formed by rapid cooling (quenching) of austenite which traps carbon atoms that do not have time to diffuse out of the crystal structure.
Titanium (pronounced /taɪˈteɪniəm/) is a chemical element with the symbol Ti and atomic number 22. It is a light, strong, lustrous, corrosion-resistant (including to sea water and chlorine) transition metal with a grayish color. Titanium can be alloyed with iron, aluminium, vanadium, molybdenum, among other elements, to produce strong lightweight alloys for aerospace (jet engines, missiles, and spacecraft), military, industrial process (chemicals and petro-chemicals, desalination plants, pulp, and paper), automotive, agri-food, medical prostheses, orthopaedic implants, dental endodontic instruments and files), dental implants), sporting goods, jewelry, and other applications.[1] Titanium was discovered in England by William Gregor in 1791 and named by Martin Heinrich Klaproth for the Titans of Greek mythology.
The element occurs within a number of mineral deposits, principally rutile and ilmenite, which are widely distributed in the Earth's crust and lithosphere, and it is found in almost all living things, rocks, water bodies, and soils.[1] The metal is extracted from its principal mineral ores via the Kroll process[2], or the Hunter process. Its most common compound, titanium dioxide, is used in the manufacture of white pigments.[3] Other compounds include titanium tetrachloride (TiCl4) (used in smoke screens/skywriting and as a catalyst) and titanium trichloride (used as a catalyst in the production of polypropylene).[1]
The two most useful properties of the metal form are corrosion resistance, and the highest strength-to-weight ratio of any metal.[4] In its unalloyed condition, titanium is as strong as some steels, but 45% lighter.[5] There are two allotropic forms[6] and five naturally occurring isotopes of this element; 46Ti through 50Ti with 48Ti being the most abundant (73.8%).[7] Titanium's properties are chemically and physically similar to zirconium.
Characteristics
Physical
A metallic element, titanium is recognized for its high strength-to-weight ratio.[6] It is a light, strong metal with low density that, when pure, is quite ductile (especially in an oxygen-free environment),[18] lustrous, and metallic-white in color. The relatively high melting point (over 1,649 °C or 3,000 °F) makes it useful as a refractory metal.
Commercial (99.2% pure) grades of titanium have ultimate tensile strength of about 63,000 psi (434 MPa), equal to that of some steel alloys, but are 45% lighter.[5] Titanium is 60% heavier than aluminium, but more than twice as strong[5] as the most commonly used 6061-T6 aluminium alloy. Certain titanium alloys (e.g., Beta C) achieve tensile strengths of over 200,000 psi (1380 MPa).[19] However, titanium loses strength when heated above 430 °C (800 °F).[5]
Due to their high tensile strength to density ratio,[6] high corrosion resistance[2], and ability to withstand moderately high temperatures without creeping, titanium alloys are used in aircraft, armor plating, naval ships, spacecraft, and missiles.[3][2] For these applications titanium alloyed with aluminium, vanadium, and other elements is used for a variety of components including critical structural parts, fire walls, landing gear, exhaust ducts (helicopters), and hydraulic systems. In fact, about two thirds of all titanium metal produced is used in aircraft engines and frames.[20] The SR-71 "Blackbird" was one of the first aircraft to make extensive use of titanium within its structure, paving the way for its use in modern fighter and commercial aircraft. An estimated 59 metric tons (130,000 pounds) are used in the Boeing 777, 45 in the 747, 18 in the 737, 32 in the Airbus A340, 18 in the A330, and 12 in the A320. The A380 may use 146 metric tons, including about 26 tons in the engines.[37] In engine applications, titanium is used for rotors, compressor blades, hydraulic system components, and nacelles. The titanium 6AL-4V alloy accounts for almost 50% of all alloys used in aircraft applications.
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