Presentation on theme: " Titanium is widely distributed throughout the whole universe such as stars and interstellar dust but, after Al; Fe and Mg, titanium is the fourth most."— Presentation transcript:
Titanium is widely distributed throughout the whole universe such as stars and interstellar dust but, after Al; Fe and Mg, titanium is the fourth most abundant of structural metals and is the ninth most abundant element on the earth. Although the commercial production of titanium did not begin till 1950's by the Titanium Metals Company of America (TMCA), this element has been recognized over at least 200 years, which is first discovered in minerals now known as rutile. Titanium exists in most minerals such as ilmenite (FeTiO 3 ); rutile (TiO 2 ); arizonite (Fe 2 Ti 3 O 9 ); perovskite (CaTiO 3 ) and titanite (CaTiSiO 5 ). 2
Titanium was first discovered by the Reverend William Gregor in 1790 who was a clergyman and amateur mineralogist. Little interest was shown in the discovery by Martin Heinrich Klaproth, a German chemist, in There was a close agreement between Gregor’s discovery and his investigations on a black sand contained 51% iron oxide; 42.25% titanium oxide; 3.5% silicon oxide and 0.25 magnesium oxide (ilmenite) and Klaproth’s investigations on a wine-red crystal which is known as rutile (titanium oxide). 3
4 Interests in the properties of titanium started after the Second World War, in the late 1940s and the early 1950s, Especially in USA, Government sponsored programs led to the installation of large capacity titanium sponge (the product type of kroll process) production plants, for example at TIMET (1951) and RMI (1958). The identity of two substances established soon and Klaproth applied the temporary name of "Titanium" after the Titans, the powerful sons of the earth in Greek mythology.
5 In Europe, large scale sponge production started in 1951 in UK. In France, titanium sponge was produced for several years but discontinued in In Japan sponge production started in 1952 and two companies, Osaka Titanium and Toho Titanium had relatively large capacities by By 1979, The Soviet Union became the world's largest titanium sponge producer. Worldwide capacity of titanium sponge increased steadily from 1980 till 1990, because of the aerospace industry and military market. But it dropped sharply from 1990 to 1995 due to the military budget decrease in USA and finally, after the minimum in 1994 it increased again which was the result of the pick up in commercial aero planes sales.
6 The production of ductile, high purity titanium still proved to be difficult, because of the strong tendency of this metal to react with oxygen and nitrogen. There are some commercial methods for producing titanium like: sodium reduction process (or Hunter process); direct oxygen reduction process; electrolytic process. But, the most famous titanium production method is Kroll process. It is removed from the titanium by distillation under very low pressure at a high temperature spongy and porous,“titanium sponge”
7 Due to main features of titanium: High strength to weight ratio, Low density, High corrosion resistance, Biocompatible (non-toxic and it is not rejected by the body), This metal is a very applicable material for many uses.
8 Titanium applications generally are classified into several main groups : Aerospace Applications: such as engines and airframes. Chemical Processing: Many chemical processing operations specify titanium to increase equipment lifetime. Petroleum: In petroleum exploration and production, flexible titanium pipe's light weight, makes it an excellent material for deep sea production risers.
9 Automotive applications: Particularly in motorcycling racing, This area is extremely challenging because of its cost sensitivity. Consumer products: such as spectacle frames; cameras; watches; jewelries and various kinds of sporting goods. Biomedical field: Such as surgical implements and implants. Architectural applications: Such as exterior walls and roofing materials.
10 Pure titanium crystalline structure undergoes a transformation from hcp (α – at lower temperature) to bcc (β – at higher temperature) by increasing the temperature up to 882 o C and The mentioned single-phase regions are separated by two-phase region of α+β. Alloying elements in titanium are usually classified in two groups of α and β stabilizing additions depending on whether increase or decrease α/β transformation temperature of 882 o C.
11 Effect of alloying additions on equilibrium phase diagrams of titanium alloys (schematically)
12 α stabilizers : Substitutional elements such as Al, Sn, Ga, Ge and etc. ; Interstitial elements such as O;N and C. Thus, unalloyed titanium and titanium alloys with α stabilizers (either singly or in combination) are called α- alloys which have hcp crystalline structure. Al is the main alloying addition in this kind of alloys and increases the transformation temperature. there is another group of α-alloys in which there is a small amount of ductile β-phase (1 to 2 percentage of Mo or Si exist) is called Near α-alloy.
13 α- alloys and Near α- alloys have moderate mechanical strength, good fracture toughness and good creep resistance. They can be easily welded and they don not need heat treatment. But, due to the presence of some amount of ductile β phase in Near α- alloys, they may be heat treated and are hot forged. Alloying elements in both mentioned group provide solid solution strengthening.
14 β stabilizers : are categorized into two groups of β isomorphous elements (which are mentioned as fully stabilized β phase) and β eutectoid forming elements (which are mentioned as partially stabilized β phase).. β isomorphous elements such as Mo; V; Nb and Ta. β eutectoid stabilizers such as Fe; Cr; Mn; Co; Cu; Si and H. There are some elements such as Zr, Hf and Sn which are neutral. They lower the α/β transformation temperature slightly and then increase it again at higher concentration. This kind of titanium alloy is heat treatable and All β alloys contain small amount of aluminum which is an alpha stabilizer. The most highly β stabilized alloys are alloys such as Ti-3Al-8V-6Cr-4Mo-4Zr and Ti-15V- 3Cr-3Al-3Sn. β alloys are exceedingly formable and they are not suitable for low temperature applications (unlike α-alloys which are suitable for cryogenic applications.)
15 α+β alloys: α+β alloys support a mixture of α and β at room temperature They may contain (10-50)% β stabilizers at room temperature. If they contain more than 20% β stabilizers, the weld ability decreases. Because : On quenching – decomposes to hcp martensite Aluminum (Al) is added to the alloy as α-phase stabilizer and hardener due its solid solution strengthening effect. Vanadium (V) stabilizes ductile β-phase, providing hot workability of the alloy. The most important alpha-beta alloy is Ti-6Al-4V. High strength alpha-beta alloys include Ti-6Al-6V-2Sn and Ti-6Al-2Sn-4Zr-6Mo. They are stronger and more readily heat treated than Ti-6Al-4V. Titanium α-β Alloys have high tensile strength and fatigue strength, good hot formability and creep resistance up to 425 ° C.
Ti-Al Alloy System Al is soluble up to ~16 wt% in α- Ti - and raises the α/β transformation temperature from. 882 to 1172 o C An alloy with 16 wt% Al will precipitate the brittle d-phase on cooling – so a-phase solid solution alloys are usually limited to <7 wt % Al High Al content causes good strength characteristic and oxidation resistance up to 600°C. (Aluminum is the most widely used alloying element in titanium alloys, because it is the only common metal raising the transformation temperature and having large solubility in α and β phases.)
17 CP (commercially pure) titanium offers excellent corrosion resistance in most environments, except those media that contain fluoride ions. Titanium alloys show less resistance to corrosion than CP titanium and the main problem with them appears to be crevice corrosion which occurs in locations where the corroding media are virtually stagnant. Titanium has limited oxidation resistance in air at temperatures above approximately 650 o C, Titanium and its alloys resist H 2 S and CO 2 gases at temperatures up to 260 o C. Unalloyed titanium is highly resistant to the corrosion normally associated with many natural liquid environments including seawater (almost 18 years); body fluids and fruit and vegetables juices. Molten sulfur; many organic compounds (including acids and chlorinated compounds) and most oxidizing acids have essentially no effect on this metal. How?
18 The excellent corrosion resistance of titanium alloys results from the formation of very stable; continuous highly adherent and protective oxide film. Titanium corrosion resistance becomes weak in very strong oxidation environments; presence of fluoride ions; continuous wear or sliding contact conditions with other metals. In such situations, the protective nature of the oxide film and its stability and integrity can be improved substantially by adding inhibitors to the environment. These naturally formed films are typically less than 10nm thick and are invisible to the eyes.
19 A corrosion inhibitor is a chemical compound that, when added to a liquid or gas, decreases the corrosion rate of a material, typically a metal or an alloy. The effectiveness of a corrosion inhibitor depends on fluid composition, quantity of water, and flow regime. A common mechanism for inhibiting corrosion involves formation of a coating, often a passivation layer, which prevents access of the corrosive substance to the metal.
20 Hydrogen chemically reacts with a constituent of the metal to form a new microstructural phase such as hydride which accumulates on the grain boundaries of metallic components.Thus, makes it brittle α+ Hydride
21 Hydrogen can be absorbed and diffuse into Titanium. If it does, the dissolved hydrogen can severely embrittle titanium. The potential for embrittlement is increased where hydrogen flow rates are high or where the coating on titanium becomes damaged. The strong stabilizing effect of hydrogen on the β phase field results in a decrease of the alpha-to-beta transformation temperature from 882°C to a eutectoid temperature of 300°C.
22 The maximum hydrogen solubility in β phase can reach as high as 50% at elevated temperatures above 600 o C. However, in α phase the solubility is only 7% at 300 o C and decreases rapidly by decreasing temperature. Why? the higher solubility in β phase results from the relatively open body centered cubic structure which consists of 12 tetrahedral and six octahedral interstices. In comparison, the hexagonal close packed lattice of α phase exhibits only 4 tetrahedral and 2 octahedral interstitial sites.
When only α phase is present, degradation is insensitive to external hydrogen pressure, since hydride formation in α phase can occur at virtually any reasonable hydrogen partial pressure. In alpha + beta alloys, when a significant amount of β phase is present, hydrogen can be preferentially transported within β lattice and will react with α phase along the α/β boundaries. Since β alloys exhibit very high terminal hydrogen solubility and do not readily form hydrides, until lately they were considered to be fairly resistant to hydrogen, except possibly at very high hydrogen pressures. 23
24 Three different kinds of hydrides have been observed around room temperature. The δ – hydrides (TiH x ) which has fcc structure with hydrogen atoms occupying tetrahedral interstitial sites. (X = 1.55 to 1.99). At high hydrogen concentrations (X≥1.99), δ hydride transforms to the diffusion-less ε- hydride with fct (face centered tetragonal) structure (c/a≤1 at temperature below 37 o C). At low hydrogen concentration of (1-3) % the metastable γ-hydride forms, with fct structure of c/a higher than 1.