titanium and its alloys ppt show
TRANSCRIPT
MM 207:Engineering metallurgy, IIT Bombay.
Titanium is recognized for its high strength-to-weight ratio.
It is a light, strong metal with low density , Is quite ductile when pure (especially in an
oxygen-free environment),lustrous, and metallic-white in color.
The relatively high melting point makes it useful as a refractory metal.
7th most abundant metal
The world production of titanium is nevertheless very small, hundreds of thousands of tonnes, which compares say with steel at 750 million tonnes per annum.
Atomic number = 22 Atomic weight = 47.9 Electronic configuration + [Ar]4S2 d 2
Atomic radius = 144.2 Melting point = 1668 Boiling point = 3287 Oxidation state = 4,3,2
Pure titanium melts at 1670oC and has a density of 4.51 g cm-3. It should therefore be ideal for use in components which operate at elevated temperatures, especially where large strength to weight ratios are required.
UTS = 375 MPa upto 1.4 GPa for Beta alloys 45 lighter than steel Hard anddifficult to machine Looses strength above 430 degrees Celsius Burns in oxygen and nitrogen Low electrical and thermal conductivity
Titanium is resistant to dilute sulphuric and hydrochloric acid, most organic acids, damp chlorine gas, and chloride solutions.
Titanium metal is considered to be physiologically inert.
Good performance in sea waer environment Around 50% of Ti used as Ti6Al4V
Reduction of ore to sponge
Melting of sponge to form an ingot
Primary fabrication into a billet/bar,..
Secondary fabrication into finished shape
Dimorphic; hexagonal alpha form changes to high temperature Beta very slowly above 880 degree celsius
The crystal structure of titanium at ambient temperature and pressure is close-packed hexagonal (α) with a c/a ratio of 1.587. Slip is possible on the pyramidal, prismatic and basal planes in the close-packed directions. At about 890oC, the titanium undergoes an allotropic transformation to a body-centred cubic β phase which remains stable to the melting temperature.
Hexagonal close-packed (hcp) or alpha (α) phase, found at room temperature
Body centered cubic (bcc) or beta (ß) phase, found above 883 °C (1621 °F)
Alpha and near alpha alloys : Ti-2.5Cu, Ti-5Al-2.5Sn, Ti-8Al-1V-1Mo,Ti-6242 , T i-6Al-2Nb-1Ta-0.8 Mo, Ti-5Al-5Sn-2Zr-2Mo
Alpha + Beta alloys: Ti-6Al-4V, Ti-6Al-6V-2Sn, Ti-6Al-2Sn-2Zr-2Cr-2Mo, Ti-8Al-1Mo-1V, Ti-3Al-2.5V
The beta phase is normally in the range of 10 to 50% at room temperature.
Beta alloys Ti-13V-11Cr-3Al, Ti-8Mo-8V-2Fe-3Al, Ti-10V-2Fe-3Al, Ti-15-3
Pure metallic titanium (99.9%) was first prepared in 1910 by Matthew A. Hunter by heating TiCl4 with sodium in a steel bomb at 700 – 800 °C in the Hunter process.[2]Titanium metal was not used outside the laboratory until 1946 when William Justin Kroll proved that it could be commercially produced by reducing titanium tetrachloridewith magnesium in what came to be known as the Kroll process
All elements which are within the range 0.85-1.15 of the atomic radius of titanium alloy substitutionally and have a significant solubility in titanium.
Elements with an atomic radius less than 0.59 that of Ti occupy interstitial sites and also have substantial solubility (e.g. H, N, O, C).
The ease with which solutes dissolve in titanium makes it difficult to design precipitation-hardened alloys.
Boron has a similar but larger radius than C, O, N and H; it is therefore possible to induce titanium boride precipitation.
Copper precipitation is also possible in appropriate alloys.
Molybdenum and vanadium have the largest influence on β stability and are common alloying elements. Tungsten is rarely added due to its high density. Cu forms TiCu2 which makes the alloys age-hardening and heat treatable; such alloys are used as sheet materials. It is typically added in concentrations less than 2.5 wt% in commercial alloys.
Zr, Sn and Si are neutral elements. These do not fit properly and cause changes in the lattice
parameters. Hydrogen is the most important interstitial. Body-centred cubic Ti has three octahedral interstices per atom whereas c.p.h. Ti has one per atom. The latter are therefore larger, so that the solubility of O, N, and C is much higher in the α phase.
If a solute differs in its atomic size by more than about 15% from the host, then it is likely to have a low solubility in that metal. The size factor is said to be unfavourable.
If a solute has a large difference in electronegativity (or electropositivity) when compared with the host, then it is more likely to form a compound. Its solibility in the host would therefore be limited.
A metal with a lower valency is more likely to dissolve in one which has a higher valency, than vice versa.
creep resistance superior to beta alloys. suitable for somewhat elevated temperature
applications sometimes used for cryogenic applications. have adequate strength, toughness, and weldability
for various applications are not as readily forged as many beta alloys. cannot be strengthened by heat treatment.
have good forging capability. cold formable when in the solution treated
condition. prone to a ductile to brittle transition
temperature. can be strengthened by heat treatment; are
solutioned followed by aging to form finely dispersed particles in a beta phase matrix.
Alloys with beta contents less than 20% are weldable.
normally have good formability ( Ti-6Al-4V is fairly difficult to form)
Solution treatment : components are quickly cooled from a temperature high in the alpha-beta range or even above the beta transus.
Aging : generates a mixture of alpha and transformed beta.
Microstructure depends on the cooling rate from the solution temperature.
Titanium can catch fire and cause severe damage in circumstances where it rubs against other metals at elevated temperatures. This is what limits its application in the harsh environment of aeroengines, to regions where the temperature does not exceed 400oC.
80% of all the titanium produced is used in the aerospace industries. Car suspension springs could easily be made of titanium with a great reduction in weight but titanium is not available in the large quantities needed and certainly not at the price required for automobile applications. The target price for titatnium needs to be reduced to about 30% of its current value for serious application in mass-market cars.
Pure titanium has excellent resistance to corrosion and is used widely in the chemical industries. There is a passive oxide film which makes it particularly resistant to corrosion in oxidising solutions. The corrosion resistance can be further improved by adding palladium (0.15 wt%), which makes hydrogen evolution easier at cathodic sites so that the anodic and cathodic reactions balance in the passive region
Titanium is capable of absorbing up to 60 at.% of hydrogen, which can also be removed by annealing in a vacuum. Hydrogen enters the tetrahedral holes which are larger in b.c.c. than c.p.h. Thus the solubility of hydrogen is larger in β. The enthalpy of solution of hydrogen in Ti is negative (ΔH<0).
the solubility actually decreases with temperature. This contrasts with iron which shows the opposite trend.
Because of this characteristic, titanium is a candidate material for the first wall of magnetically confined fusion reactors. The hydrogen based plasma is not detrimental since at 500oC and 1Pa pressure, the Ti does not pick up enough hydrogen for embrittlement. An additional feature is that Ti resists swelling due to neutron damage
Surgical Implants Prosthetic devices Jet engines Chemical processing plants Pulp and paper industry Marine applications Sports equipment
F67Part 2Unalloyed titanium – CP grades 1-4 (ASTM F1341 specifies wire)F136Part 3Ti6Al4V ELI wrought (ASTM F620 specifies ELI forgings)F1472Part 3Ti6Al4V standard grade (SG) wrought (F1108 specifies SG castings)F1295Part 11Ti6Al7Nb wrought-Part 10Ti5Al2.5Fe wroughtF1580-CP and Ti6Al4V SG powders for coating implantsF1713-Ti13Nb13Zr wroughtF1813-Ti12Mo6Zr2Fe wrought
http://journals.tubitak.gov.tr/engineering/issues/muh-07-31-3/muh-31-3-2-0608-14.pdf
