an
Materials
of
Construction Review
Less Common Metals by E. M. Sherwood, Battelle Memorial Institute, Columbus, Ohio N e w methods of fabrication, involving electron-beam equipment, should permit even wider use of these versatile materials
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INTEREST
in the less common metals continued to grow at a rapid rate during the past year. The large number of general review articles which appeared is an important measure of this interest. Many of the more than 700 technical publications relating to these metals were reviews. Perhaps the greatest stride forward took place in the further development of rather exotic means, such as electron beam processing, to refine, melt, shape, and join the more refractory but less oxidation-resistant members of this group. Vacuum-arc skull melting and levitation melting process equipment were used to secure metals of higher purity with improved properties. The less common metals were bonded to themselves and to stainless steel using special organic adhesives to permit economy of their use in special corrosive media. Protective coatings for these metals were applied by electrodeposition and by vapor deposition. Evaluation of physical and mechanical characteristics, as well as corrosion resistance of the newer metals, were intensively reviewed. I t was predicted that future developments would lead to the increased use of less common metals in transportation, aircraft, missile, and other military equipment, as well as in new industrial applications. As an example, important progress in he development of refractory sheet metal structures was announced. As in past years, the greatest number of publications dealt with zirconium
prepared by electrolysis and hydrogen reduction treatments (83), was forged and rolled, and the general nature of its hot-working characteristics was determined (84). Further studies verified earlier conclusions that nitrogen is the most significant impurity having an influence on the ductile-to-brittle transition of massive chromium and chromium-base alloys (7). Alloy additions of chromium to molybdenum and tungsten improve their ability to withstand conditions of hightemperature oxidation, erosion, and corrosion (82).
Hafnium Although high-purity hafnium has only one important application, namely, as a neutron absorber in nuclear reactors, a great deal has been done to obtain material of suitable quality (8). An entire book devoted to the metallurgy of hafnium was published (76). I n particular, the mechanical, physical, and corrosion properties of high-purity iodide hafnium were evaluated (27).
Molybdenum Although its shortcomings are well recognized, molybdenum still is considered to be the “vanguard” material for space vehicles (44). Amelioration of such room-temperature problems as cracking is now considered feasible. The need for structura1 members of reasonably large size in many applications has put pressure on metallurgists for further development of methods of casting (77) and fabrication (3, 44, 8 7 ) . Consumable-electrode arc-melted molybdenum now can be centrifugally cast with reasonable freedom from flaws and anisotropy as a result of purification during melting and controlled solidification. Detailed reviews of welding and brazing and general fabrication were worthwhile additions to the literature. The necessity for effective protective coatings to resist high-temperature oxidation has been an incentive for devising many elaborate and complex protectivecoating schemes (25, 33). A large number of coatings are potentially useful, but all have faults. To date, multilayer electrodeposited coatings have
Chromium Partly as a result of increased development and use of halide processes in metallurgy, attention was called to the commrrcial availability of anhydrous CrC13 (4). Another semicommercial development was the compacting of highpurity chromium powder in a steel jacket, followed by extrusion to make seamless tubing (80). Pure chromium,
The complete bibliography for the 1959-60 Materials of Construction Review of the Less Common Metals.
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given the best service life for molybdenum parts such as nozzle guide vanes. Impact ductility (53) and short-time creep-rupture behavior (28) were evaluated. An important alloy is that containing 0.5% (weight) titanium (79, 30, 67). Thorough studies of its characteristics were carried out. An alloy containing 0.2 to 0.5% (weight) zirconium is stronger than the 0.57, (weight) titanium alloy, while one with 5.0% (weight) titanium and 0.257, (weight) carbon possesses a very high recrystallization temperature. Information on many molybdenum alloy systems became available 122). Molybdenum0.5y0 (weight) titanium alloy sheet metal structures were fabricated successfully (43). Coatings which permit use of molybdenum as a bearing material a t elevated temperatures include MoSz and MoSi2 (66).
inert gases or vacuum "atmospheres" are a must to prevent contamination by atmospheric gases during annealing and welding. Niobium reacts a t a linear rate with air in the temperature range 600" to 1200' C. (24, 36, 37), the high solubility and diffusion rate of oxygen causing embrittlement. Nitrogen does not affect this reaction. Binary additions for improving oxidation resistance include chromium, molybdenum, titanium, and vanadium. Molybdenum, titanium, and tungsten as alloying agents influence the high temperature mechanical properties and recrystallization temperature of niobium. A proprietary coating and a modified Si-Cr alloy are reasonably effective as protective coatings. Niobium borides (52) have high resistance to attack by acids and N a O H at room temperature, while tin (2),in the solid solubility range, promotes higher hardness and greater resistance to corrosion.
Niobium
Rhenium
Several important summaries of up-todate information on niobium and its properties were published during the period covered by this review (70, 27, 57, 67). Improvements in extractive processes have made the metal and its alloys readily accessible to the designer as engineering materials of importance. There are signs of progress in the development of niobium-based "super alloys" for gas turbine and rocket applications, as well as of its growing use in the steel industry and in the electronic and nuclear engineering fields. Estimates were given (67) of possible future consumption of niobium in various fields of application. High-purity iodide niobium was prepared (64). Pure niobium can be fabricated cold using conventional tools (35). Purified,
Small amounts of rhenium became available on a commercial basis in 1959 (77, 32). Extremely high melting point and good metallic properties make possible its increased use in situations where a relatively high cost can be tolerated. When alloyed with molybdenum it provides a metal with improved characteristics, as compared with molybdenum, and of lower cost than pure rhenium (7).
Tantalum Two comprehensive reviews were published concerning tantalum and its properties (57, 55). High purity iodide tantalum was prepared and evaluated (65). Recommended procedures for tungsten-inert gas arc welding of tan-
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INDUSTRIAL AND ENGINEERING CHEMISTRY
talum were described (75). Electronbeam melting was used in the development of a Ta-W alloy having high tensile strength a t elevated temperatures (47). The excellent corrosion resistance of tantalum has led to good service life of tantalum equipment in the chemical and petrochemical industries (78,
34). Tungsten Current research on tungsten (6, 78) seeks to improve its purity, its fabrication characteristics, and its oxidation resistance. Extrusion of arc-cast tungsten ingots (20), and development of new and improved methods of fabrication (9, 73) have shown tungsten to be one of the best metals for hightemperature design Tungsten's rate of oxidation undergoes transition from predominantly linear to parabolic as temperature is increased ('69). Vapor deposition of high-purity tungsten for use as a high-temperature coating, with retention of strength above 2000' C. under nonoxidizing conditions, was achieved (62).
Zirconium Advances in casting ( 5 ) ,welding ( 7 4 , and working (29) zirconium were reported. Improvements in metallurgical techniques led to the production of metal of higher purity having better corrosion resistance (39-47). Lowhafnium zirconium. pre-etched in an aqueous HF-HNO3 solution, corroded more rapidly by an order of magnitude than did unetched material under similar conditions (77). Metallic additions of nickel to zirconium increase hydrogen pickup during corrosion. Antimony, chromium, and iron appear t o decrease hydrogen pickup, while tin has little or no effect ( 7 3 ) . The only slip system observed in zirconium over the temperature range 77' to 1075°K. was of the form (lOi0) [i2iO] (60). Anistropy of expansion of zirconium results in internal strains during quenching which are responsible for the absence of an elastic limit (76). New light was shed on the details of the a-0 allotropic transformation in zirconium (42, 23). The deformation which accompanies transformation is much more severe in zirconium than in titanium, for example. Alloys of zirconium with aluminum, tin, and molybdenum, while having corrosion resistance in sodium at 1000° F. comparable to that of unalloyed zirconium, demonstrate short-term elevated-temperature strength characteristics a t 1050" and 1200" F. equal t o
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o r greater than that of Type 304 stainless steel (87). Data were presented for Zr-Mo-Sn and Zr-Nb-Sn alloys indicating strengths as high as 190,000 p.s.i. with reasonable ductility (63). Exposure of Zircaloy-2 simultaneously to steam and irradiation produces corrosion accompanied by local swelling and fissures (54). Bonding of Zircaloy-2 to itself and to Type 304 stainless steel must be accomplished with a high degree of reliability (38, 56, 85). Diffusion bonding a n d gas-pressure bonding operations were described. Electron-microscopical examination of bonds produced a t 500’ F. a n d 350,000 p.s.i. during a 1-hour pressing cycle showed a n almost complete absence of pitting. New structures, fabricated from zirconium and Zircaloy2 , were described (26,50, 72). Zircaloy-2 properties were summarized (86). The diffusion coefficients for oxygen in @-Zircaloy-2 and Zircaloy-3 were about 10 times greater than those for nitrogen in high-purity &zirconium (46).
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(21) Francis, E. L., U. K. Atomic Energy Authority Rept. IGR-R/R-304 (Oct. 16, 105R\ /.
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(22) Freeman, R. R., Briggs, J. Z., “Molybdenum Metal Constitution Diagrams,’’ Climax Molybdenum Co., New York, 1959. (23) Gaunt, P., Christian, J. W., Acta Metallurgaca 7, 534-43 (August 1959). (24) Gemmell, G. D., Trans. Am. Inst. Mzning Met. Petrol. Engrs. 215, 898-901 (December 1959). (25) Giancola, J. R., U. S. Air Force Tech. Note WADC-TN-241 (June 1959). (26) Goodwin, 3. G., Metal Progr. 77, 93-6 (April 1960). (27) Goodwin, J. G., Lorenz, F. R., Nuclear Sci. and Eng. 6, 49-56 (July 1959). (28) Green, W. V., Smith, M. C., Olson, D. M., Trans. Am. Inst. Mzning. Met. Petrol. Engrs. 215, 1061-6 (December 1959). (29) Grimes, G. G., Am. Machinist 104, 143, 145 (March21, 1960). (30) Hall, R . W., Sikora, P. F., Natl. Aeronautics Space Admin. Memo. 3-959-E (February 1959). (31) Hetherington, J. S., ed., “Proc. First Symposium on Electron-Beam Melting,” Alloyd Research Corp., Watertown, Mass., 1959. (32) Ind. Heating 26, 977-8, 980 (May 1959). (33) Jaffee, R. I., in “Fabrication of Molybdenum,” pp. 119-33, Am. SOC. Metals, Novelty, Ohio, 1959. (34) Kelberine, L., Chim. @ ind. (Parts) 82, 20-2 (July 1959). (35) Klopp, W. D., Defense Metals Inform. Center Memo. No. 34 (Sept. 11, 1959). (36) Zbid., No. 123 (Jan. 15, 1960). (37) Klopp, W. D., Maykuth, D. J., others, U. S. Atomic Energy Comm. Rept. BMI-1317 (Feb. 3, 1959). (38) Koopman, K. H., in “Minutes 7th Annual Atomic Energy Commission Welding Conference,” U. S. Atomic Energy Comm. Rept. TID-7562 (January 1959). (39) Kuhn, W. E., Chem. Eng. 67, 155-60 (Feb. 8, 1960). (40) Kuhn, W. E., Corrosion 15, 103t(March 1959). zd., 16, 136t-144t (March 1960). 42) Langeron, J. P., Lehr, P., Rev. Met. 56, 307-15 (August 1959). (43) Levy, A. V., Bramer, S. E., in “Developynt of Refractory Sheet Metal Structures, ; Metal Progr. 76, 180-3 (September 1959). (44) Levy, A. V., Bramer, S. E., S.A.E. Journal 67, 41-6 (August 1959). (45) Levy, A. V., Bramer, S. E., SOC. Automotive Engrs., Preprint No. 56-T, (1959). (46) .Mallett, M. W., Albrecht, W. M., Wilson, P. R., J . Electrochem. SOC.106, 181-4 (1959). (47) Mastick, D. F., Iron Age 185, 98-9 (April 7, 1960). (48) Merriam, J. C., Materials in Design Eng. 51, 105-20 (January 1960). (49) Metal Progr. 77, 127-8 (April 1960). (50) Miller, E. C., Adamson, G. M., in Prog. in Nuclear Energy, Ser. 5, Metallurgy and Fuels 4, 159-66 (1959). (51) Miller, G. L., “Metallurgy of the Rare Metals,” Vol. 6, “Tantalum and Niobium,” Academic Press, New York, 1959. (52) Modylevskaya, K. D., Samsonova, G. V., Ukrain. Khim. Z h w . 25, 55-61 (January 1959). (53) Nature 184, 897 (1959). (54) Nuclear Power 4, 86 (July 1959).
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Materials of Construction Review (55) Ogden, H. R., Defense Metals Inform. Center Memo. No. 32 (Aug. 28, 1959). (56) Paprocki, S. J., Hodge, E. S., others, U. S. Atomic Energy Comm. Rept. BMI-1312 (Jan. 20, 1959). (57) Parr, N. L., “Zone Refining and Allied Techniques,” George Newnes, Ltd., London, 1960. (58) Powell, C . F., Materials in Design Eng. 51, 98-101 (January 1960). (59) Pugh, J. W., High Temperature Materials Conf., Cleveland, 1957, pp. 306-18 (1959). (60) Rapperport, E. J., Hartley, C. S., U. S. Atomic Energy Comm. Rept. NMI-1221 (Aug. 12, 1959). (61) Redden, T. K., in “High Temperature Materials,” pp. 292-305, Wiley, New York, 1959. (62) Reid, W. E., Brenner, A,, Natl. Bur. Standafds ( U . S.) Tech. News STR2470 (January 1960). (63) Robinson, H. A , , Doig, J. R., others, Trans. A m . Soc. Mining Met. Petrol. Engrs. 215, 237-45 (April 1959). (64) Rolsten, R. F., J . Electrochem. SOC. 106, 975-80 (November 1959). (65) Rolsten, R. F., Trans. Am. Inst. Mining Met. Petrol. Engrs. 215, 472-6 (June 1959). -.-.
(66) R’dwe, G. W., Sci. Lubrication (London) 11, 12-15 (October 1959). (67) Sandor, J., Metallurgia 59, 185-94 T i l 1959). (68 Schwartzberg, F. R., Ogden, H. R., affee. R. I.. Defense Metals Inform. Center Rept. No. 114 (1959). (69) Semmel, J. W., in “High Temperature Materials,” Wiley, New York, 1959. (70) Shepard, S. W., Am. SOC. Mech. Engrs., Paper No. 59-MD-7 (1959). (71) Smith, T., J . Electrochem. SOC.107, 82-6 (1960). (72) Spalaris, C. N., Nuclear Sci. and Eng. 6, 37-43 (July 1959). (73) Stambler, P., Space Aeronautics 32, 48-51 (July 1959). (74) Stark, L. E., Welding Engr. 44, 50-1 (October 1959). (75) Steel 146, 206-10, 212-14 (Jan. 4, 1960). (76) Thomas, D. E., Hayes, E. T., eds., “The Metallurgy of Hafnium,” U. S. Govt. Printing Off., Washington, D. C., 1960. (77) Thuston, G. H., Western Machinery and Steel World 50, 63-5 (March 1959). (78) Tietz, T. E., J. Metals 11, 763-4 (November 1959). (79) Torti, M. L., Ham, J. L., Steel 144, 64-6 (March 9. 1959). (80 Un’ion Carbide Metals Rev. 2, 8-10 &all 1959). (81) Wagner, R. K., Kline, H. E., Trans. Am. SOC.Metals 52, Preprint No. 169 (1959). (82) Wkare, N. F., Monroe, R. E., Defense Metals Inform. Center Rept. No. 108 (March 1, 1959). (83) Wegman, R. F., Bodnar, M. J., Machine Design 31, 139-40 (Oct. 1 , 1959). (84) Wilson, J. W., Space Aeronautics 33, 45-9 (March 1960). (85) Yoshida, S., Ohba, Y., Trans. Natl. Research Inst. Metals (Tokyo) 1, No. 1 , (1959). (86) .Yo‘shida, S., Ohba, Y., Nagata, N., Nzppon Kanzoku Gakkaishi 24, 16-20 (1960). (87) Young, A. P., Schwartz, C. M., U. S. Atomic Energy Comm. Rept. BMI1364 lJulv 29. 1959). (88) Zima,‘G. E., Zbid., HW-60908 (Oct. 14, P959).. VOL. 52, NO. 12
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