Titaniumand its uses in aircraftMicrosoft ClipArt

Titanium is a metallic element which was discovered in 1791, although it has only come into common usage over the past 50 years. It has various atomic properties which give it useful macroscopic properties. These properties make titanium and its alloys effective materials for use in aircraft.http://www.mac-life.de/wallpapers/

Chemical symbol: Ti Atomic Number: 22 Atomic Weight: 48 Standard state: Solid Density: 4.54 g cm-3 Melting Point: 1933 K Boiling Point: 3560 K Forms +2, +3 and +3 ions First isolated in 1910. Modern production uses the Kroll method, where titanium ores are reacted with chlorine and carbon. Fractional distillation separates the products, which are then reduced with magnesium. Titanium is the fourth most common structural element in the Earths crust, found in minerals such as menachanite, ilmenite and rutile.Titanium: the Factshttp://cfa-www.harvard.edu/~scranmer/Gifs/periodic_table.gif

The three main categories of titanium alloys are alpha, beta and alpha-beta, beta being used for heavy duty purposes. In the polycrystalline structure, the atoms can be arranged in two main forms of lattice alpha, with a close-packed hexagonal layout, and beta, with a body-centred cubic arrangement. Unalloyed titanium changes from the alpha form to the beta form above 880C. One of the most commonly used alloys, Ti6Al4V is an alpha-beta alloy, which means that its structure is a mixture of the two.Atomic StructureBody-centred cubicHexagonal close-packedhttp://people.bath.ac.uk/ma3yp/titanium/whatisit.html

G. Burton et al., Sallters Advanced Chemistry - Chemical Ideas, Heinemann Educational Publishers, 2000In these arrangements, the atoms of the different metals in the alloy are in an ionised form, held together by a sea of electrons which have been delocalised from the atoms of the elements. This non-directional metallic bonding is very strong in titanium due to the number of electrons available for delocalisation. The free electrons also make these materials electrical and thermal conductors. As the metal ions can slide past each other one at a time in the sea of electrons, metallic substances are malleable and ductile. Physical PropertiesSea of delocalised electrons surrounding positive metal ions.

In these arrangements, the atoms of the different metals in the alloy are in an ionised form, held together by a sea of electrons which have been delocalised from the atoms of the elements. This non-directional metallic bonding is very strong in titanium due to the number of electrons available for delocalisation. The free electrons also make these materials electrical and thermal conductors. As the metal ions can slide past each other one at a time in the sea of electrons, metallic substances are malleable and ductile. Physical Properties Dislocation Atoms can move individually. When an atom moves, the dislocation moves.Atom moves Dislocation moves Dislocation reaches edge of crystal, causing a step.J. Ogborn & M. Whitehouse, Advancing Physics AS 2000, Institute of Physics Publishing, 2000

However, elements such as oxygen, nitrogen and carbon (sometimes called interstitial alloys) insert themselves in the lattice and prevent relative sliding of the molecules, giving the titanium a greater tensile strength. The presence of atoms other than titanium in the alloys also makes them more resistant to creep, as the sliding of the atoms is reduced. Finally, titanium and many of its alloys, like most other metals, are resistant to cracking. Due to their ductility, small cracks do not propagate they only get broader.Physical PropertiesIn titanium alloy, the dislocation is pinned by the interstitial atoms, reducing its ductility.J. Ogborn & M. Whitehouse, Advancing Physics AS 2000, Institute of Physics Publishing, 2000

However, elements such as oxygen, nitrogen and carbon (sometimes called interstitial alloys) insert themselves in the lattice and prevent relative sliding of the molecules, giving the titanium a greater tensile strength. The presence of atoms other than titanium in the alloys also makes them more resistant to creep, as the sliding of the atoms is reduced. Finally, titanium and many of its alloys, like most other metals, are resistant to cracking. Due to their ductility, small cracks do not propagate they only get broader.Physical PropertiesJ. Ogborn & M. Whitehouse, Advancing Physics AS 2000, Institute of Physics Publishing, 2000 High Stress Reduced StressStress Stress Stress Stress

The effect of these microscopic properties which make titanium so useful can be seen through its macroscopic properties:Macroscopic Properties

PropertyTitaniumAluminiumIronDensity (kg m-3)450727007874Youngs Modulus (GPa)11670211Tensile Strength (MPa)240 (Unalloyed) to 1170,Ti6Al4V: 87590 to 180 (varying with impurities)1000(high tensile steel)Electrical Resistivity (10-8m)402.659.7Thermal conductivity(W m-1 K-1)2223580Coefficient of Linear Thermal Expansion(K-1 multiplied by 106)8.623.111.8

Out of these properties, several make titanium and titanium alloys very useful in the construction of aircraft. They can be cast, forged or moulded to make various parts. Most notable is their low density although not as light as aluminium, they are much less dense than steel. Titanium and its alloys strong atomic lattice gives them better characteristics when heated than other metals, shown by its low coefficient of linear expansion. At high supersonic speed, aluminium alloys would expand too much and fail, whereas titanium expands comparatively little. Finally, its reasonable tensile strength and Youngs Modulus, mean that it can support the varying loads which aircraft are subject to whilst in flight.Uses in Aircraft

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In the Lockheed-Martin F-22 Raptor Advanced Tactical Fighter, 42% of the structural weight consists of titanium.http://www.deneba.com/community/artgallery/images/cv9/aircraft.jpgThe Materials Information Society, Introduction to Selection of Titanium Alloys, ASM International, 2002

The majority of aircraft constructed since around 1960 have used small amounts of titanium to some extent, such as the previous examples. However, some aircraft have been constructed virtually entirely from titanium alloys. The 1962 A-12 (later SR-71 Blackbird) designed to over-fly Soviet Russia was capable of altitudes over 85,000 feet at speeds of 2,000 mph, Mach 3.2. In order to be light enough to reach this speed and at the same time withstand high temperatures of 500 C it was made mostly of titanium alloy, which expands by 15 cm in flight.Titanium Aircraft

The SR-71 BlackbirdWhen the aircraft is not in operation, the titanium alloy panels are not a perfect fit to compensate for the expansion at high speed flight. This results in fuel leaking from the seams!http://www.dfrc.nasa.gov/Gallery/Photo/SR-71/Medium/EC97-43933-4.jpg

Before aircraft began to use titanium around 50 years ago, many other materials were used. The first aircraft used stressed canvas over their wings with simple wooden frames. These are light, but not very strong, so in the first aircraft structural failures were common. Later, metals and alloys began to be used in aeroplanes. Steel skins were used for a short time, but these were heavy and limited the performance of aircraft. Aluminium based alloys such as duralumin were then used, which are reasonably strong and light.Before Titanium

On many aircraft of the First World War such as this Nieuport 24 biplane the wings were prone to breaking off when the aircraft went into a dive!http://www.warbirdsovernewzealand.com

Improvements in metallurgy allowed for lighter and stronger alloys to be made which could be more heat-resistant or cheaper than other materials. Today, aircraft are mostly constructed from steel and aluminium alloys, with titanium alloys for purposes which other materials cannot match, especially where high temperatures are involved. In the future, aircraft may be made from a new generation of very strong titanium-based ceramic materials. Perhaps they will not be constructed out of metals at all, but advanced plastics and composite materials. Although titanium is very much a material of the moment, it might not be long until scientists make a successor to itModern Aircraft

Are there already aircraft made from exotic materials flying at secret testing sites such as Area 51 in the US or Zhukovski in Russia?The NASA prototype forward-swept wing X-29 was constructed mainly out of carbon fibre, which is less likely to warp in flight than metal alloys.http://www.dfrc.nasa.gov/Gallery/Photo/X-29/Medium/EC87-0182-14.jpg

In the space of less than 100 years, titanium has gone from being just another element to one of the more commonly used metals today, particularly in aircraft, but also in medicine, jewellery and even as a white pigment. Although its crystalline structure gives it great strength and it has a relatively low density, its main advantage is its fantastic performance at high temperatures. When alloyed with aluminium and vanadium it can become more versatile. You only have to look around you to see how much we utilise this fantastic material and the extent to which it contributes to modern life.Summaryhttp://www.taiwan.co.jp/exhibition/exh-2/titanium/titan03.jpg

Introduction to Selection of Titanium Alloys by The Materials Information Society Onboard the A380 by Airbus UK Alchemy of a Supermetal by Steven Ashley, Scientific American magazine, October 2003 Sticky Fingers by Barry Fox, New Scientist magazine, October 2002 BAe Systems, http://www.baesystems.com A to Z of Metals, http://www.azom.com Properties of Titanium, http://www.roymech.co.uk/Useful_Tables/Matter/Titanium.html This presentation can be accessed at http://www.freewebs.com/basicsoftware/titanium.ppt Selected Bibliography

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Pure titanium is rarely used in aircraft, as it is extremely expensive and can be difficult to weld, although it is only about two-thirds the density of steel. More often, commercially pure (CP) grades of titanium are used, though their tensile strength is much lower than that of other alloys. Usually, it is alloyed with other metals such as aluminium, manganese and vanadium, to produce strong, lightweight materials, that are capable of operating at a wide range of temperatures. Titanium alloys are very durable, although they can be more susceptible to frictional wear damage than other materials of similar hardness. These properties result from the titanium and its alloys polycrystalline structure.Titanium: the Facts

The new Airbus A380 uses a wide range of materials, including titanium, for different purposes.Although it does not have to withstand such high temperatures as military aircraft, it must still be light so that it can be fuel efficient.http://www.baesystems.com/gallery/air/images/Airbus_A380hires.jpg

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