MATERIALS O F CONSTRUCTION
Titanium b The titanium industry i s now making a strong recovery since its first decline in late 1957 and 1958. Mill shipments in 1959 are expected to be about 50% greater than ihe estimated 2500 tons shipped last year. b About 95% of American production is sti!l being used in military aircraft. An important development i s incorporation of the metal into original designs of military and nonmilitary equipment where improved performance and economics dictate its use. Chemical applications are expanding with a high order of confidence, and long-range forecasts indicate the automobile industry should become an important consumer. These trends predict a more stable but expanding industry.
Downloaded by UNIV OF CAMBRIDGE on September 2, 2015 | http://pubs.acs.org Publication Date: September 1, 1959 | doi: 10.1021/ie51397a033
THE
growth, status. and trends of the titanium industry were discussed very ably by Tyler (26A) and others (5A, 73'41. Unparalleled rapid grov th occurred since 1951 from militari requirements and considerable governmental support. T h e Department of Defense remains active in providing funds for processing research. Leading producers have also invested their own resources into developments and increased plant capacity. This effort resulted in growth and accomplishments which would have required a generation under ordinary circumstances. However. time was too short to establish the metal in civilian applications, so that a business decline was inevitable in 1958 with the reduction in military purchases. Essentially all of today's tonnage is produced by the Kroll process which emplovs magnesium or sodium for the reduction of titanium tetrachloride. Now an electrorefining process has been developed, using fuscd halide salts, which yields metal of exceptional purity HOWARD B. BOMBERGER is supervisor, Fundamental Research Section, Midland Research Laboratory, the Crucible Steel Co. of America. As most titanium i s being used in aircraft, the author's experience with Wright Aeronautical Corp., and Crucible Steel's titanium activities (formerly Rem-Cru Titanium, Inc.) gives him a balanced view of titanium picture both from the standpoint of producer and a principal consumer. He obtained his B.S. in metallurgy from Pennsylvania State University (1942), and his M.S. (1950) and Ph.D. (1952) from Ohio State University. He is author of several papers and has patents in the fields of corrosion and titanium metallurgy. He i s a member of American Society of Metals, NACE, Electrochemical Society, and Sigma Xi.
1 228
b Research efforts to improve quality and reduce costs have been effective, and considerable effort is being made to develop more efficient winning methods. b lmpottant advances have been made in alloys which place titanium products in a more competitive position. Most important are new Formageable sheet alloys which are formed readily in the solution trea,ed condition but can then b e aged to very high strengths. b A full line of mill products i s available for the consumer, and most production and fabrication techniques have been reduced to routine operations. Furthermore, the metal has been field tested extensively in military and chemical applications.
from contaminated and mixed scrap (77A). Numerous p t r n t s have been issued on ivinning methods \vhich employ fused salts as electrolytes. Approaches such as this may eventually replace the Krolltype processes. For example; Ervin and others ( 4 4 ) obtained high purity metal by using inexpensive titanium carbide anodes in molten halide salts. Electrorefining methods, and a small but growing castings industry (7A, 75A, 76A) are viewed as promising solutions to the serious scrap problem. Pertinent data on halide equilibria werereported recently (6A, 8A, 9A, 74A.) Improvements in arc melting and mill technology have resulted in better quality and the availability of essentially all mill forms. Details on fabrication are available in the literature and from most suppliers. .4 number of reports covered machining ( 7 A , ZA, 70A, 72A)> spinning ( 2 4 4 , cold extruding (ZOA), hot forming (22.4): lvelding (3.4, I I A ) , and adhesives (7-electrolytic and electroless methods, but hydrogen pickup and incomplete oxide removal before plating can be troublesome (27A, 254). Both conventional electrolytic and electroless methods have been used to apply chromium for overcoming galling and seizing. Xliller 764) reported that
INDUSTRIAL AND ENGINEERING CHEMISTRY
metallic coats, especially nickel, offer the best solution to the titanium friction problem. Others have shown that cyanide; nitride, and fluoride coats are also effective. Some paraffinic and inorganic halogen compounds show benefit as lubricants. Glycol derivatives and sugar solutions were found to be better than conventional lubricants.
Alloys and Mechanical Properties Titanium is considered a light metal, with a density about 60% that of steel but about 6070 greater than aluminum. Commerically pure grades are supplied with yield strengths ranging between 40,000 and 90,000 p.s.i. Considerably higher strengths are obtained by alloying and heat treatments. The strengthdensity ratio is titanium's most publicized characteristic. Concentrated alloy research resulted in rapid advances, with an average of more than one new alloy per year since 1951. Three distinct types are recognized, depending on their crystallographic structure: alpha: beta, and alpha-beta. As noted by Frost (ZB, 3B) they have a wide range of characteristics. The alpha alloys are noted for their toughness, hot strength (up to llOOo F.), weldability, and oxidation resistance. T h e new alpha alloys are the intermediate strength alloys (Ti-8A1-IMoIV and Ti-8Al-2Cb-lTa) and the super strength alloys (TTi-8Al-8Zr-lTa-kCb and Ti-12Zr-7Al). Alpha-beta alloys are noted for their forgeability, formability, and heat-treatability. Recent alloys of this type are Ti-4.41-3Mo-1V and Ti-lGV-2,jAl. These are used primarily in the form of sheet (3B, 5B). Recently, Crucible Steel announced the availability of the first heat treatable beta alloy, It is weldable and has excellent formability. After forming it can be aged to strengths above 250,000 p s i.-the highest strengths per unit
....................................................
weight so far obtained by any commercial material (7B,4B, 5B).
Downloaded by UNIV OF CAMBRIDGE on September 2, 2015 | http://pubs.acs.org Publication Date: September 1, 1959 | doi: 10.1021/ie51397a033
Applications Most of the titanium in this country is used in the compressor chamber of the Pratt and Whitney 5-57 and 5-75 jet engines. These operate in the temperature range of 200' to 700' F. where titanium alloys show their greatest advantage. The finished parts weigh about 300 to 600 pounds, respectively. About 10 to 209", of the titanium in military aircraft is in the airframes. This percentage may increase with the availability of the newer alloys ( 72C). The Royal Canadian Air Force's CL-28 bomber employs 2700 pounds of titanium in various locations with overall weight savings of 900 pounds. T h e new Convair jet transports are expected to use as much as a ton of sheet, extrusions, and fasteners. Special, highly efficient constructions, such as honeycomb and sandwich structures, are being developed \virh titanium (72C). Some metal is going into missile design. For example, Ti-6A1-41- alloy is formed into 24-inch spheres, heat treated to 160,000 p.s.i. yield strength to contain helium at -300' F . and 5000 p.s.i. (8C, 9C). The major civilian use today is also in aircraft, with a 50% increase noted last year over 1957. T h e Boeing 707 uses about 1000 pounds, Douglas' DC-8 almost 2500 pounds, and Convair's 880 about 1000 pounds per plane (7C,
7C) * T h e greatest advance in civilian consumption was in the process industries where titanium's corrosion resistance is especially attractive. Columbia-Southern concluded from an extensive inplant test program that the metal's performance is so outstanding that more general use can be readily justified on a purely economic basis (4C). Recently Wirta (74C) of General Electric discussed on-site welding and practical applications in corrosive solutions. His analysis showed reductions in maintenance and replacement costs by judicious combinations of titanium and stainless steel. A titanium tube bundle in concentrated nitric acid was still serving well after running seven times longer than the previous material. Barron (7C) and Caterson (2C) cited a number of applications including titanium condensers, heat exchangers, pump impellers, shafts, steam jet diffusers, and packing supports in a chlorine-caustic tower. I n these applications, titanium lasted from five to 25 times longer than other materials. Watkins (73C) noted that plates and springs of Ti-4A1-4Mn are serving well after 18 months' service in compressors handling nitrogen and hydrogen in an
ammonia process. Previous material suffered corrosion fatigue in periods from a few weeks to nine months. Titanium is also used in the form of heating coils in chrome-sulfuric acid plating solutions with a life expectancy of 20 years. Certain food; drug, dyestuff, and chemical processes are also employing the metal where contamination cannot be tolerated. T h e recovery of waste heat from corrosive chemical plant effluents has been made feasible with titanium heat exchangers. New designs are taking better advantage of the metal's properties such as light weight, high strength, and resistance to corrosion fatigue. T h e latter property can be important, For example, the fatigue strength of mild steel in sea water is reduced more than 8070; and chromium-nickel austenitic steels by 30y0. but the fatigue strength of titanium appears to be higher in sea water than in air (5Cj. Titanium is used widely in anodizing racks where its good performance is d u e to an oxide film which prevents corrosion and minimizes current loss. Cotton (3C, 6C,77C)recently discovered that platinized titanium has electrode characteristics similar to solid platinum. Films as thin as a few tenths of a mil to a few microinches seem to be adequate to serve as inexpensive, nonsoluble, lowovervoltage electrodes. This material appears attractive for anodes in electrochemical cells-especially for hypochlorite and chlorine cells-and cathodic protection systems. T h e economical range of current density appears to be between 25 and 75 ampereslsq. ft.
Chemical Properties T h e corrosion resistance of titanium has been studied for a number of years and is now well known. Detailed performance data were reported in earlier reviews. Most of recent work has been aimed a t specific applications and basic studies. The metal has excellent resistance to natural environments and most chemicals. The notable exceptions are certain concentrations of hydrofluoric, hydrochloric, sulfuric, phosphoric, oxalic, formic, and trichloracetic acids. Dry halogen gases and liquids and ionizable fluoride compounds also attack the metal. Oxidizing agents, even in small amounts, frequently inhibit corrosion in otherwise corrosive solutions. Outstanding performance \vas reported for the metal in solutions of chloride and hypochlorite salts: nitric acid, \vet chlorine, aqua regia, and many other chemicals ( 7 7 0 ) . Wilson and Gegner ( 2 6 0 ) recently confirmed earlier laboratory tests by extensive plant testing. A number of reports appeared which VOL. 51,
..........~.. ......_.._.._......._.___.-..--..-.---TITANIUM
help to explain the remarkable corrosion resistance of titanium. Passivity is attributed to a thin adherent oxide film which can be enhanced by almost any oxidizing agent and many metal ions. For example, Gleekman (720) reported that 5%, (volume) or more of chlorine in an air mixture added to joycsulfuric acid reduced the corrosion rate about 100-fold. Additions u p to 100% chlorine had the same effect. Rates of 0.1 mi1,'year were observed in SOYc acid and 1.5 mildyear in 877, acid-both containing chlorine at 70' and 80OF.: respectively. Buck and Leidheiser ( 3 0 ) noted that very- small additions of noble metal ions to 2 M hydrochloric acid reduced corrosion to a negligible value. This agreed well ivith earlier work by Schlain and Uhlig and Geary who noted that copper and oxidizing agents have a similar effect. Buck and Leidheiser ( 4 0 , 5 0 ) also noted that mere contact with noble metals in the solution was adequate to passivate the metal. Stern ( 2 2 0 ) correlated the effect of inhibitors with potential measurements and showed that they result in a passive potential. A number of workers confirmed the early important work of M a and Peres by- sho\ving that anodizing reduces corrosion markedly by depositing a thicker: more-resistant oxide film. As little as 0.5 to 1 volt and 0.5 to 1 ampere: sq. cm. are adequate to arrest corrosion in ?8Yc sulfuric acid ( 2 0 , 2-10). Rysselberghe and Johansen ( 2 0 0 ) studied the kinetics of anodic oxidation. Inglis and Cotton (730) described a practical application in which a titanium tank, tubes and centrifugal pump under a small d.c. voltage handled 40% sulfuric acid at 60' C. for six weeks tvithout noticeable corrosion. Ruediger and Fischer ( 7 9 0 ) achieved passivation in hydrofluoric acid solutions by the same method. Eisenberg and DeLaRue (700) studied anodic polarization in nonaqueous etching baths of hydrofluoric acid and organic solvents. Cotton 190) found that titanium can be anodically polarized to passive potentials in boiling formir, oxalic and 40% sulfuric. and 35% phosphoric, 40Y0 sulfuric. and concentrated hydrochloric acid all at 60' C. The small potential required can be obtained externally or by coupling with a more noble metal. A coating of platinumeven if thin and discontinuous-is verv effective. .As noted earlier. platinized titanium shoivs promise for use as insoluble anodes. .4n anode with only 5 microinches of platinum appeared to be unaffected at a current density of 100 amperes'sq. ft. for 250 hours. but an unplared specimen failed in 30 minutesi700: 7 8 0 ) . NO. 9, P A R T II
SEPTEMBER 1959
1229
Downloaded by UNIV OF CAMBRIDGE on September 2, 2015 | http://pubs.acs.org Publication Date: September 1, 1959 | doi: 10.1021/ie51397a033
Noble metals enhance the potential usefulness; platinized titanium has attractive electochemical properties, and an alloy of 0.1% palladium has greater resistance to reducing acids Titanium is unique in its ability to polarize and, therefore. resist anodic corrosion when in contact with dissimilar metals. Kenahan and Schlain (7,5D: 760). however, found that when titanium is coupled with aluminum in 0.l.V sulfuric or 1% oxalic acids it, being the more noble, undergoes slow “cathodic” corrosion. T h e surface film is not very stable in the acids used and becomes even less stable under the somewhat stronger reducing conditions which prevail when the metal is made cathodic. iYhen titanium was coupled with stainless steel in sulfuric acid, it became the anode member of the couple. Less than normal corrosion was noted. These authors also found that titanium alloys also have excellent resistance to many chemicals, but, in general, the unalloyed metal is more resistant under severely corrosive conditions. Copper alloys were cited as an exception, as they have better resistance to sulfuric acid. Stern ( 7 0 . 8 0 , 740) made the important discovery that small alloying additions of noble metals markedly improve the corrosion resistance of titanium in reducing acids without altering the metal’s already excellent resistance to oxidizing acids or its mechanical properties. Sato ( 7 7 0 ) studied similar alloys in Japan and noted the same general effect. As little as 0.1% palladium appears to be adequate and practical; it should extend titanium’s usefulness well into the area of reducing acids and to those highly corrosive solutions which change in process from oxidizing to reducing or vice versa. Although oxidizing agents tend to inhibit the corrosion of titanium, the metal is not completely resistant to powerful oxidants such as fuming nitric acid. Rittenhouse and Papp (78D), however, reported that 1 to 2% water inhibits corrosion in red fuming nitric acid. Seals (270) noted that Ti-23%Zr alloy, unlike unalloyed titanium, has excellent resistance to 90% hydrogen peroxide at 77’ F. Work at Oak Ridge National Laboratory (6D)showed that solid titanium can ignite and burn with a steady flame in a n atmosphere containing a t least 3570 oxygen if a fresh surface is formed promptly-such as in breaking a tensile coupon-to initiate the reaction. T h e temperature is not important in the range of 20’ to 300’ C. Pressures of 350 p.s.i. or more are needed for ignition in pure static oxygen, but pure, moving oxygen need only be at 50 p.s.i. for ignition. Wallwork and Jenkins (25D) studied
1230
the mechanism of oxidation in air! and Anderson and coworkers ( 7 0 ) reported a large number of oxide phases not previously observed. The corrosion of titanium by molten sodium chloride was explained as being due to oxidation to T i 0 0 . 2which is then slowly oxidized to titanium dioxide in the salt (230). Literature Cited Production and Fabrication (1A) Bauer, G. LV., A m . SOC.Tool E n g . Collected Papers 58, 1-4 (1958). (2.4) Bauer, G. W., Tool E n g . 40, 121-3 (May 1958). (3Al Canonico, D., Schwartzbart, H., Welding J . (.V. Y.138, 71s-7s (February 1959). (4A) Ervin, G., Jr., Ueltz, H. F. G., byashburn, hl. E., J . Electrochem. SGC.106, 144-6 (1959); (5A) Euster, T. B., Barron’s, 3-4, 16-8 (Feb. 23, 1959). (6A) Fortin. B. J.. others, J . Electrochem. SOC.106, 428-33 (1959). (7.4) Garret, J. H., Huddle, F. P., .Vfodern Castzngs 34, 18-21 (August 1958). (8-4) Hall, E. H., Blocher, J. M., Jr., J . Electrochem. SOC. 105, 40-3 (1958). (9.4) Hall, E. H., Blocher, J. M., Jr., Campbell, I. E., Ibzd., 271-8 (1958). (IOA) Hansen, J. V. E., Clough, P. J., hifachine Deszgn 30, 28-30 (April 1958). (11.4) Hoefer, H. W., Weldzng J . (’V. Y.) 37,467-77 (1958). (12.4) Iron A g e 181, 126-8 (.4pril 24, 1958). (13A) Ibtd., 183, 29 (Jan. 8, 1959). (14.A) Komarek, K., Hcrasymenko, P., J . Electrochem. Sod. 105, 210-9 (1958). (15A) M e t a l Bull. 25 (Dec. 2, 1958). (16A) Miller. P. D.. W e a r 2, 133-40 (NO’ vember 1958). ’ (17A) Nettle, J. R., Hill, T. E., Jr., Baker, D. H.. Jr.. U. S. Bur. Mines Rept. Invest.’5410 (1958). (18.4) Pattee, H. E., Faulkner, C. E., Rieppel, P. J., Light .Vfetal Age 16, 22-4, 27, 33 (December 1958 1 ; Battelle Mem. Inst. T M L Rept. 104 (June 1958). (19.4) Prod. E n g . 29, 38 (Dec. 8, 1958). (20.A) Quodt, R . A , , A m . SOC.Tool E n g . Coiiected Papers 58, 1-8 (1958). (21.4) Saubestre, E. B., J . Electrochem. SGC. 106, 305-9 (1959). (22A) Selmer, E., Tool Eng. 42, 101-3 (February 1959). (23x1 Shelley, R. C., Welding and M e t a l Fabrication 27, 31-2 (1959). (24.4) Spiegl, F., A m . SOC.Tool Eng. CGllected Papers 58, 1-3 (1958). (25.4) Steel 142, 102, 104 (May 5, 1958). (26.A) Tyler, P. M., M e t a i Progr. 74, 97100, 170-4 (July 1958).
Alloys and Properties (1B) Crucible Steel Co. of America, Pittsburgh, Pa., Data Sheet B-12OVCA (March 1959). (2B) Frost, P. D., M e t a l Progr. 75, 95-8 (March 1959). (3B) Ibid., 91-6 (April 1959). (4B) J . M e t a l s 11, 29-32 (1959). (5B) Machine Design 30, 12, 14 (July 10, 1958). Applications (IC) Barron, L. J., Petrol. Eng. 30, C12 (September 1958).
INDUSTRIAL AND ENGINEERING CHEMISTRY
(2C) Caterson, A. G., A m . M e t a l .2larket 65, 9, 18 (Oct. 29, 1958). ( 3 C ) Chem. A g e (London) 81, 9 [Jan. 3, 1 c)qo) A,u,,.
(4‘2) Chem. Eng. AVews37, 145 (March 23, 1959). (5C) Corrosion Precention CYControl 5, 37-9 (June 1958). (6C) Cotton, J. B., Platinum Metals Rev. 2 , 45-7 (April 1958). (7C) Crucible Titanzum Reo. 6, No. 1 (1958). (8C) Zbzd., 7, No. 1 (1959). (9C) Durstein, R. C., Modern M e t a l s 14, 64-5 (April 1958). (IOC) M e t a l Bull., No. 4292, 25 (1958). (11CI Metal Ind. (London) 94, 28 (Jan. 9, 1959). (12C) Tyler, P. M., M e t a l Progr. 74, 10912, 170-82 (September 1958). (13C) Watkins, R. J., Ind. Chemist 34, 2826 (1958). (14C) Wirta, R. MI.,Modern M e t a l s 15, 78, 80, 82 (March 1959). Chemical Properties (ID) Anderson, S., others, Acta Chem. Scand. 11, 1641-57 (1957). (2D) Andreeva, V. V., Kazarin, V. I., Doklady Akad. N a u k S.S.S.R.121, 873-6 (1958). (3D) Buck, W. R., Leidheiser, H., Corroszon 14, 308t-12t (July 1958). (4D) Buck, W.R., Leidheiser, H., J . Electrochem. Soc. 105, 158C (1958). (5D) Buck, W. R., Leidheiser, H., .?;attire 181, 1681-2 (1958). (6D) Chem. E n g . News 36, 36-7 (Xug. 4. 1958). (7D) Ibtd., 37, 26 (April 13, 1959). (8D) Chem. Eng. Progr. 55, 114, 120 (April 1959)
(11D) Cotton, J. B., Brad. t 3 Ind. (London) 1958, pp. 640-6. (12D) Gleekman. L. W., Corrosion 14, 21-2 (September 1958). (13D) Inglis, N. P., Cotton, J. B., Corrosion Prevention C8 Control 5, 59-63, 73 (November 1958). (14D) Iron Age 183, 129-30 (April 16, 1959).
(15D) Kenahan, C. B., Schlain, D., Corrosion 14, 25-8 (September 1958). (16D) Kenahan, C. B., Schlain, D., U. S . Bur. Mines Rept. Invest. 5423 (1958). (17D) Ratha, F. L., Melbourne, Australia, Publ. 6053158. (18D) Rittenhouse, J. B., Papp, C. .4., Corrosion 14, 283t-384t (June 1958). (19D) Ruediger, O., Fischer, W. R., Z. Elektrochem. 62, 803-10 (1958). (20D) Rysselberghe, P. V., Johansen, H. A., J . Electrochem. SOC.106, 355-8 (1959). (21D) Seals, W., Reaction Motors, Inc., Denville, N. J., Rept. EML-1002 (Oct. 10, 1957). (22D) Stern, M., J . Electrochem. SOC.105, 638-47 (1958). (23D) Straumanis, hf. E., Chiou, C., Z . Elektrorhem. 62, 201-9 (1958). (24D) Tomashov, N. D., Al’tovskil, R. M., Arakelov, A. G., Dokiady Akad. N a u k S.S.S.R. 121, 885-8 (1958). (25D) Wallwork, G. R., Jenkins, A. E., J . Electrochem. SGC.106, 10-14 (1959). (26D) Wilson, W.,Gegner, P. J., Corrosion 15, 80 (1959).
