Copyright © 1994 ASM International ® All rights reserved. Materials Properties Handbook: Titanium Alloys, 06005G www.asminternational.org 1960s has served to somewhat offset the in each ofthe alloys Ti-6Al-2Sn-4Zr-2Mo decline in military demand during the (i.e., "Ti-6242"), Ti-6Al-2Sn-4Zr-6Mo (i.e., same period, thereby yielding not only a "Ti-6246"), and Ti-11.5Mo-6Zr-4.5Sn (i.e., Titanium is widely distributed netgrowth but a relatively steady one. "~-III") was on the increase. Today the al­ throughout the universe. It has been dis­ Titanium (meaning titanium and its loy Ti-6242 to which about 0.1% Si has covered in the stars, in interstellar dust, alloys) has two principal virtues: (1) a been addedis beingusedintitanium alloy in meteorites, and on the surface of the high strength/weight ratio and (2) good forgings andhas received extensive study earth. Its concentration withinthe earth's corrosion resistance. At one time or an­ and use in its role as a gas-turbine com­ crust of about 0.60/0 makes it the fourth other practically all aerospace structures pressor-disc material. Finallyit shouldbe most abundant of the structural metals -airframes, skin, and engine compo­ noted that Ti-10V-2Fe-3Al has been the (after aluminum, iron, and magnesium). nents-have benefited from the introduc­ beneficiary ofthe renewed interest being It is 20 times more prevalent than chro­ tion of titanium. Nonaerospace applica­ shown in so-called "near-~" titanium al­ a mium, 30 times more than nickel, 60 tions include steam-turbine blades, loys [DUE80 ] [l'ER80] [TOR80], while it is times more than copper, 100 times more hydrogen-storage media, high-current! atlast becomingrecognizedthat Ti-5ONb, than tungsten, and 600 times more than high-field superconductors, condenser one ofthe most important oftoday's tech­ molybdenum. This abundance is to some tubing for nuclear and fossil-fuel power nical superconductors, is in fact a ~-Ti al­ extent illusory, however, in that titanium generation, and other corrosion-resistant loy [CoL81]. is not so frequently found in economically applications such as components for extractable concentrations. Concentrated ocean thennal-energy conversion, off­ sources of the metal are the minerals il­ shore oil drilling, marine-submersible menite, titanomagnetite, rutile, anatase, vessels, desalination plants, waste-treat­ In order to cope with unexpected in­ and brookite. ment plants, the pulp-and-paper indus­ creases in the demand for a metal, it is Ilmenite is haematite (Fe203) in try, and the chemical and petrochemical helpful to be able to rely on a copious and whichhalfoftheironhasbeenreplacedby industries. stable supply of the basic ore. The tita­ titanium; titanomagnetite is magnetite Interest in the properties of titanium nium industry is fortunate in this regard. (Fe304) in which one-third ofthe iron has and its alloys began to accelerate in the Titanium dioxide is produced in large been replaced by titanium. Rutile is Ti02 late 1940s [CRA49] and early 1950s as quantities for many applications, so much (as are anatase and brookite). Naturally their potential as high-temperature, so that in 1977, for example, only a few occurring (and titanium-deficient) il­ high-strength/weight materials with percent of the world's production of tita­ menite consists ofhaematiteparticlesin a aeronautical applications became more nium ore was tapped for metallic sponge matrix of ilmenite; naturally occurring and more widely recognized. The history refinement (most of the mined ore being (and, again, titanium-deficient) ti­ oftitanium andits developmentinalloyed used to make paint pigment). Thus, since tanomagnetite is magnetite containing form has beendescribedin detailinthein­ the overall demandfor rawmaterialis not lathsofilmenite. Inshort, themostimpor­ troduction to the first International Con­ subjectto the same fluctuations as the de­ tant titanium minerals are ilmenite and ference on the subject [JAF70] and in the mand for the metal, should the latter un­ rutile. introduction to ZWICKER's comprehensive dergo a significant increase at any time, Titanium was first discovered in min­ metallurgical treatise Titan und TItanle­ there is at least a strong raw-material erals now knovvn as rutile by W Gregor gierungen [ZWI74]. As evidenced by the base from which to draw. (England) and M.H. Klaproth (Gennany) papers presentedatthe subsequentInter­ Industry's growing awareness of the in about 1790. The first commercial mill national Conferences, titanium andits al­ need for energy conservation has served products were produced by the Titanium loys have by now found widespread use in to emphasize an unfortunate charac­ Metals Company of America (TMCA) the aerospace industry (for both frame teristic of the current methods of tita­ around 1950. From that time to the pres­ andengine components) andinthe chemi­ nium metal refinement: their energy in­ ent, production ofthe metal has grown at cal and related industries, where advan­ tensiveness. The energy required to an average annual rate of about 8%. Su­ tage can be taken oftheir corrosion resis­ produce a ton ofsponge-titanium from its perimposed upon part of this temporal tance. According to WOOD [Woo72], by are is 16 times that needed to produce a growth curve is a largefluctuating compo­ 1972 about 30 commercial alloys were al­ ton of steel, 3.7 times that needed for fer­ nent, a reminder ofthe capriciousness of ready on the marketinmill-product form. rochrome, 1.7 times that needed for alu­ the materials demands of the aerospace Ofthese, the eight most favored composi­ minum production, and a little more than industry, titanium's principalmarket dur­ tions, accounting for some 900/0 of the that needed for a I-ton ingot of magne­ ingthe early years. Fortunatelyfor the ti­ sales, were three grades ofunalloyedtita­ sium. Since, however, the heats offorma­ tanium-production industry, the 13% an­ nium and the alloys Ti-5Al-2.5Sn, Ti-6Al­ tion ofrutile (- -228 kcallmol), haematite nual growth rate exhibited by the civilian 4~ Ti-8Al-1Mo-1~ Ti-6Al-6V-2Sn, andTi­ (- -200 kcallmol), and magnetite (- -268 sector ofthe total market since the early 13V-11Cr-3Al. At that time also, interest kcall mol) are in the ratio of 1:0.88:1.18, Copyright © 1994 ASM International ® All rights reserved. Materials Properties Handbook: Titanium Alloys, 06005G www.asminternational.org 4/I1Jn'''~II'~1 ME~talllur·~v of Titanium Table 1.1 Total Impurity Contents of Io­ Table 1.2 Typical Interstitial Impurity Contents of Several Grades of Titanium dide- and Kroll-Process Titaniums (in wt%) [RAS72] Interstitial content, ppm Data Grade oftitanium N source Element IodideTi Kroll Ti MRC (MARZ-grade) 78 6 63 1 Mg 0.01 0.13 MRC (VP-grade) 150 40 350 2 Si 0.01 0.05 TMC electrorefined sponge (grade ELXX) 40 370 3 AI 0.02 Kroll-process (Toho sponge) 110 860 4 Fe 0.01 0.20 Kroll-process 800 400 1100 5 Ni 0.01 Iodide-process 100 200 200 5 Co 0.02 Cr 0.01 (1) Materials Research Corp.: Zone-refined; supplied typical analysis. (2) Materials Research Corp.: Vacuum Mn 0.005 0.02 melted; supplied typical analysis. (3) Titanium Metals Corp.: See also rCoL701. (4) See rCoL701. (5) See Table 1.1. C 0.01 0.08 N 0.02 0.04 0 0.02 0.11 there seems to be some scope for increas­ ucts are commercially pure sponge-tita­ wire, which acts as nucleus for the growth ing the energy efficiency ofthe titanium­ nium (in the fonn ofa porous, gray, coke­ ofa long cylindrical bar ofhigh-purity ti­ refinement process. like mass) and MgC12' most ofwhich can tanium crystals. Typical impurity con­ The most well-known method oftita­ be drained out ofthe reaction chamber as tents of several grades of titanium are a liquid. The MgC1 is electrolytically nium production is the Kroll process, 2 listedin Tables 1.1 and 1.2. recycled. The titanium sponge is conso­ which involves the reduction of TiC1 by 4 lidated by arc melting in a water-cooled These and other standard commer­ magnesium. The first step in the process copper crucible: this process involves cial methods oftitanium production, such is the preparation ofthe tetrachloride it­ several iterations ofa procedure in which as the sodium-reduction (or Hunter) proc­ self, which is carried out by the chlorina­ an arc is maintained between a consu­ tionofa mixture ofcarbonwithrutileoril­ ess, the direct-oxide-reduction process, mable compacted-sponge-titanium elec­ andthe electrolytic process, have been de­ menite. The Kroll magnesium-reduction trode and a pool ofmolten sponge. scribed in detail by MCQUILIA'I [McQ56, reaction takes place in a closed heated re­ The highest purity titanium is pre­ Chap. 2], HOCH [HoC73b], and ZWICKER actor vessel under an inert atmosphere. pared for research purposes by the iodide Liquid TiC14 is introduced to the liquid process. Crude titanium is first reacted [ZWI74, pp. 21-27J, while some new ap­ magnesium already presentinthe vessel, withiodinein aninert atmosphere toform proaches developed in the Soviet Union thereby initiating the reaction 2Mg + titanium iodide. This can then be decom­ have been outlined by REzNICHENKO and TiCl4 -7 2MgC12 + Ti. The reaction prod- posed at the surface ofa heated titanium coworkers [REz82, REz82aJ..