E . M . SHERWOOD
A practical knowledge o f uacuum metallurgy is a must f o y commercial suppliers, fabricators, and users.
Evaluation o f properties will provide more useful design data
LESS COMMON METALS AND MODERN L
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CHEMICAL PROCESSING demands of space technology, Thenuclear engineering, and chemical processing for materials of construction with unusual properties have fostered numerous investigations of the less common metals as a family during the past year. Fully one third of the publications in the field during the period, June 1961 to May 1962, dealt with these metals as a group. Major emphasis was on molybdenum, niobium, tantalum, tungsten, and zirconium. The elusive combination of properties most often sought for space applications includes strength and resistance to oxidation at very high temperatures, with room temperature ductility sufficient to permit forming and fabrication. The latter is often difficult to meet even by the advanced techniques now available, The five metals mentioned above are not resistant to oxidation and must be protected by refractory coatings or alloyed with other less common metals to achieve even moderately satisfactory performance in the required environments. The brittle nature of the most successful protective coatings precludes their application prior to forming and joining, while the complex shapes required make difficult the coating of finished hardware. Nuclear engineering has rigid materials standards for neutroncapture cross section, fission product retention, ability to withstand damage during irradiation and corrosion by liquid metals, high pressure water, and superheated steam. Chemical processing places primary emphasis on fabricability and on corrosion
resistance to aqueous media and active gases a t high temperatures under varying conditions of stress. I t is significant that not one of the less common metals is completely useless in any of the areas specified. The future looks good. Research will disclose means of achieving most of the desired goals. Up-to-date consideration was given to the present status of a number of the less common metals and to the compilation of new property data (56, 67, 85). I n the case of refractory metals for engineering applications, the questions of cost and availability often limit the field to molybdenum, niobium, tantalum, and tungsten. The Fourth International Plansee Seminar had as its theme "Powder Metallurgy in the Nuclear Age" and indicated important advantages accruing from this method of fabrication for a number of the less common metals (46). I n refining, halide chemical vapor-deposition processes have much to offer. A method of correlating deposition rates and of predicting the performance of commercial units was described (62). Working, forming, and cutting less common metals by conventional and advanced techniques received much attention (53, 59,9 ? ) . Standard vacuum-processing procedures now include melting, cutting, and joining by electron beams (34,49, 60, 90). Exploitation of gas-pressure bonding as a means of joining, cladding, and welding the less common metals proved fruitful (63, 66). To determine protective coating and alloying needs, oxidation char-
acteristics were studied intensively (78). As better quality metals and alloys appeared, rapid evaluation of their mechanical properties was carried out (2, 8, 13, ?6,35). New solubility data for the less common metals in liquid metal media showed the relative compatibility with liquid sodium and potassium (21). An extensive review of current U. S. work, relating to coatings for the protection of refractory metaIs from oxidation, indicated few areas and materials not under investigation (44). Alloy studies encompassed 93 binary and 68 ternary phase diagrams of Mo, Nb, Ta, and W (26). Use of phase equilibria in various aspects of materials development proved rewarding (69). Fabrication and quality control of precision tubing for nuclear applications reached a high level of achievement (84). The metals were re-evaluated for chemical plant use (5). Beryllium. A comprehensive review included a survey of the beryllium industry (43). Practically all processing powder - metallurgy methods are useful in the consolidation of beryllium powder ( 7 ) , although vacuum hot pressing has many advantages for the production of large and short run parts. Samples of beryllium sheet, fabricated in various ways, were tested in dry carbon dioxide at 500" to 1000" C. and in oxygen a t 600" to 1000" C. (37). Break-away oxidation sets in after 1500 hours in dry COz at 1000" C. Rates of oxidation appear to depend on fabrication method used. Adequate resistance
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Uses of tantalum equipment in chemical plants continue to expand to attack by molten bismuth at 400' and 525" C. permits its use as a container in a liquid-metal fuel reactor (76). Etching to remove machining surface defects improves the mechanical properties (83). Irradiation of hot-pressed beryllium at a neutron flux greater than loz1 per sq. cm. at 280" to 480' C. produces a measurable effect on the mechanical properties (68). HOWever, appreciable recovery of properties is achieved by annealing at temperatures above 800" C. Parts, coated by natural and anodic oxidation, electroplating, and flame spraying, have improved corrosion and wear resistance (57). Chromium. New information was developed on melting and fabricating high purity chromium and the resulting material was evaluated (29). Special emphasis was given to chromium alloys containing yttrium and rare earth metals which act as scavengers for impurities. Effects of additions of other less common metals and nickel were evaluated (86). Scaling behavior of chromium in a hot gas stream apparently depends on the type of flow over the metal surface (88). There is evidence that the gas flow pattern can be a more important factor than the bulk composition of the gas. Oxide scale produced under certain conditions provides some protection against further oxidation and nitriding. The influence of impurity elements, structure, and prestrain on the ductile-to-brittle transition temperature of iodide chromium was Wrought specimens studied ( 7 ) . had a transition temperature of -10" C. The addition of a Group I1 metal oxide to electrolytic chromium produces a highly refractory coating material (74) which can be extruded, forged, and rolled.
AUTHOR E. M . Sherwood is Assistant Chief, Chemical Vapor Deposition Division, Battelle Memorial Institute. He has authored I@EC's Less Common Metals review since 7955. 58
Hafnium. Electrolytic refining of low grade hafnium at 830' C. produces material suitable for use as control rods in water-cooled reactors (55). An investigation of diffusion barriers for refractory metals shows that hafnium is one of the most promising barriers against diffusion for tungsten-base materials at 1700" C. (64). Molybdenum. Much has been added to our knowledge of the improvement in properties to be expected when electron-beam melting is used to process molybdenum (77). Further, the characteristics of binary systems of molybdenum with the other less common metals have now been thoroughly explored and promising new alloys are available. Although high purity molybdenum is relatively soft (Rockwell C about 2 0 ) , it is also gumm)and abrasive, which makes cutting operations difficult. The use of sharp carbide cutters with positive rakes, shallow cuts, and light chip loads, together with spray-mist coolants and low cutting speeds, gives excellent results (80). Much attention has been given to joining operations for molybdenum. Electron-beam welding (87), brazing, and mechanical joining methods are used. Method, atmosphere, speed of the operation, and the properties of purity, grain size, and recrystallization temperature all influence the degree of success secured (20). Coatings to protect molybdenum from oxidation at 1400" C. can be applied by flame spraying, diffusion, and electroplating (37, 62). ,4 novel method of siliconizing molybdenum parts by dipping them in molten Cu-Si at 1000" to 1500" C. (75) was described. The use of molybdenum under conditions of strong irradiation requires evaluation of properties subsequent to such exposure. Measurable damage occurs (79, 89). -41loys of molybdenum with tantalum and niobium were studied intensively ( 7 7 ) . I n addition to established uses in the electronics industry, molybdcnum finds applica-
INDUSTRIAL A N D ENGINEERING CHEMISTRY
These pieces of niobium and zirconium zceie gas-fressure bonded at 7550" F. and 10.000 f.s.i. f o r 4 hours
tion in muffles, hearths, furnace trays, jet engine nozzle throats, pigments, and lubricants ( 4 ) . Niobium. A book devoted to thc metallurgy of niobium was publishcd (77). The equipment, plant lavout, and process flowsheet for the rccently activated St. Lawrence Project in Quebec were described (25). Niobium has a bright future. But predictions vary as to when this "future" will arrivc (30, 65). Interstitial impurity levels have a pronounced effect on the beha\.ior of niobium at temperatures in the range -194' to 28' C. (74). Carbon exerts particular influence on ultimate strength, elongation, rcduction in area, and brittleness. Oxidation-rate kinetics were studied (12,38). The yield strength of niobium is particularly sensitive to nitrogen content ( 2 8 ) . Niobium and some of its alloys were corrosiontested in nuclear reactor coolants (48). Zinc coating of niobium by vacuum distillation at 790' C., hot dipping at 550' to 700' C., aqueous electroplating, or cladding eliminates contamination hardening of the substrate by formation of protective intermetallic layers (42). Corrosion problems encountered when niobium alloys are used in nuclear reactors were discussed (22). Rhenium. Metallurgical processes for extraction, consolidation, and fabrication of rhenium were reviewed (39). Special attention
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was given to mechanical properties and deformation characteristics at both low and high temperatures. Superconductivity measurements can be employed in the study of neutron irradiation damage in rhenium (10). T h e relation of superconductivity parameters to point defect and dislocation occurrence has been established. Thermocouples of tungsten and tungsten with 26y0 rhenium can be used in neutral or reducing atmospheres at temperatures up to 2300' C. (47) and may soon be useful at temperatures as high as 2750' C. Tantalum. Two reviews of tantalum metallurgy appeared (27, 57). Embrittlement can be prevented in aggressive reducing acid media by the presence of a small piece of platinum (9). T h e metal has many characteristics which recommend its consideration for use in chemical plant design (78, 36, 50, 87). New tricks in fabrication include riveting of tantalum strips to a steel base and then welding the tantalum liner to these strips in a n atmosphere of argon. Recent data indicate that tantalum alloys may be useful for parts requiring a combination of toughness at cryogenic temperatures with strength at high temperatures (58). Tungsten. Considerable effort has been expended in producing tungsten of high purity and in preparing high density compacts from the metal. Material soon may become available commercially which exceeds in purity the spectrographic standards of a few years ago. A better understanding has been secured of the mechanisms involved in the recovery of mechanical and electrical properties, recrystallization, flow and fracture, and of the influence of impurities on ductileto-brittle transition temperature ( 3 ) . T h e effects of high temperatures, pressure, and water vapor on oxidation rate were evaluated (6). High temperature reactions with other solids and gases were studied. To fabricate useful ion rocketengine emitters, 1-micron diameter tungsten powder is mixed with 2y0 (Continued on page 60)
W I T H THE A D D I T I O N OF
LOW C O S T , M O R E EFFECTIVE, DISPERSANTS By adding only .05% t o 3.0% of Marasperse (based on the weight of solids), a viscous pasty mass becomes an easy-to-handle freeflowing liquid. T h e action of Marasperse prevents, and reverts, the flocculation of insoluble particles in water suspension. Only the state of the mass is changed. T h e volume is unaffected because the Marasperse is taken into solution by the available water. T h e versatility of Marasperse dispersants is best described by the variety of applications in use, such as oil well drilling muds, gypsum slurries, ceramic slips, pesticides, dyestuffs, industrial cleaners, concrete, pigment, carbon black and clay dispersions, ore flotations, and many others. Marasperses are water-soluble, non-hygroscopic, non-fermenting, free-flowing powders. For additional information use the handy coupon.
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SEPTEMBER
1962
59
of a fugitive organic binder (77). The mixture is then cold-pressed at 25,000 p.s.i. and batch-sintered at 1500’ C. for 20 hours. Zirconium. Materials of construction proved most successful for use in nuclear reactors are hafniumfree zirconium and its alloys. \,Yhen large members are required, it is found that they may lack the uniformity of properties normally expected of wrought alloys. This is true of hammer- or press-forged Zircaloy-2 bars (72). Improvement in corrosion resistance, attainment of isotropic mechanical properties, and development of a “basketweave” structure without agglomeration of intermetallics is achieved by solution heat treatment at 850’ to 1150’ C . , followed by rapid quenching. The reaction of zirconium with cxygen under various conditions may have complex results, some of which can be put to good use. Processing Zircaloy-2 and Zircaloy-4 in dry oxygen at 400’ C. produces a nuclear core material having a black, adherent, continuous oxide film without hydrogen pickup (43). The oxidation behavior of zirconium and zirconium with 2.4-16.7 weight per cent of oxygen alloys is interpreted in terms of simultaneous oxide formation and oxy-gen dissolution in the metal (67). In Zircaloy-2 processing, an oxide surface film is formed during the water corrosion test (41, 82). Its removal by vacuum annealing is economical and rapid. The surface layer of diffused oxygen is removed by pickling. Informaticn on the reaction of zirconium with COS (33), susceptibility to stress-corrosion cracking in FeCI3 (24), and behavior in aqueous media when contaminated with reaction product from an HK03-HF-H20 etchant (40) was developed. Corrosion testing of zirconium and its alloys in high temperature water and superheated steam was widely used as a means of simulating the environment in a pressurized-water nuclear reactor (79, 32, 54, 73). The effect of such impurities as Al, N, and M n is to increase the corrosion rate, while Cu appears neutral in its action Circle N O . 12 an Readers’ Service Card
60
INDUSTRIAL AND ENGINEERING
:HEMISTRY
(75). Other impurities, such as Mg and Si, also may have an effect (70). Controlled expansion transition sections, consisting of Ki-Fe elements of the Invar type, were used to connect Zircaloy-2 members with stainless steel for use over a wide range of temperature (23). Low expansion rate at the Zircaloy-2 end was achieved by the use of 4376 Xi-Fe. High expansion rate required at the stainless steel end was obtained with 60y0Ni-Fe.
B I BL IOG RAPHY (1) Allen, B. C., Maykuth, D. J.; Jaffee, R. I., NASA Tech. Note D-837, April 1961. (2) Amateau, M. I?., Nicholson, D. W., Glaeser, W.A,, Defense Metals Inform. Center Memo. No. 106, May 12, 1961. (3) Atkinson, R. H., Keith, G. H., Koo: R. C., in “Refractory Metals and .4lloys,” Met. SOC. AIME: Vol. 11, p. 319, Interscience, New York: 1961. (4) Australasian Manujacturer 46, 86 (Nov. 11, 1961). (5) Barber, .4. H., Chem. @ Process Eng. 42, 451 (October 1961). (6) Barth, V. D.: Rengstorff, G. W. P., Defense Metals Inform. Center Rept. 155, July 17, 1961. (7) Beaver, W. TV., Larson, H. F., in “Powder Metallurgy,” p. 747, Interscience, New York, 1961. (8) Bechtold, J. H.: Wessel, E. T., France, L. L., in “Refractory Metals and Alloys.“ Met. SOC.AIME. Vol. 11, p. 25, Interscience, New York, 1961. (9) Bishop, C. R., Stern: M., Corrosion 17, 85 (August 1961). (10) Blanc, J., Goodman, B. B., others, in Proc. Seventh Inter. Conf. Low-Temperature Physics, p. 393, University of Toronto Press, Canada, 1961. (11) Braun, H., Sedlatschek, K.: in “Powder Metallurgy,” p. 645, Interscience, New York, 1961. (12) Bryant, R. T., J . Less-Common Metals 4, No. 1, 62 (February 1962). (13) Buckle, H., Technique Moderne 53, 53 (July 1961). (14) Carver, M . D . , Dunham, J. T., Kato, H.; U. S. Bur. Mines, Rept. Invest. 5872, 1961. (15) Carver, M. D., Link, R. F., Kato, H., Ibid.,5865, 1961. (16) Chang, W. H., in “Refractory Metals and Alloys,” Met. SOC.,AIME, Vol. 11, p. 83, Interscience: New York: 1961. (17) “Columbium Metallurgy” (D. L. Douglass and F. I$’. Kunz, eds.)? Met SOC., AIME, Vol. 10, Interscience, New York, 1961. (18) Corrosion Prebent. &= Control 8, v (September 1961). (19) Cox, B., J . Electrochem. Sac. 109, 6 (January 1962). (20) Cox, F. G., Welding and Metal Fabrication 29, 371 (September 1961). (21) Darras, R., Energie Nucleaire 3, 128 (March-April 1961).
c
(22) Douglas, D. L., Corroszon 17, 589t (December 1961). (23) Duff, C. G., Nuclear Science and Eng. IO, 278 (July 1961). (24) Dunham, J. T., Kato, H., U. S. Bur. Mines, Rept. Invest. 5784, 1961. (25) Eng. Mznzng J . 162, 99 (October 1961). (26) English, J. J., Defense Metals Inform. Center Rept. 152, April 28, 1961. (27) Erben, E., Lesser, R., Metal1 15, 679 (July 1961). (28) Evans, P. R. V., J . Lesc-Common Metals 4,No. 1, 78 (February 1962). (29) Fox, J. E., McGurty, J. A,, in “Refractory Metals and Alloys,” Met. SOC. AIME, Vol. 11, p. 207, Interscience, New York, 1961. (30) Frank, R. G., Zbzd., p. 237. (31) Graham, J. W., Luft, L Zbid., p. 533. (32) Greenberg, S., J . Nuclear Materzal 4, 334 (August-September 1961). (33) Gregg, S. J., Hussey, R. J., Jepson, W. B., Corroszon 17, 575t (December 1961). (34) Habraken, L., Vacuzim IO, 412 (December 1960). (35) Hall, R. W., Sikora, P. F., Ault, G. M., in “Refractory Metals and Alloys,” Met. SOC., AIME, Vol. 11, p. 483, Interscience, New York, 1961. (36) Hampel, C. A., Corroszon 17, 9 (October 1961). (37) Higgins, J. K., Antill, J. E., J . Nuclear Materials 5 , 67 (January 1962). (38) Hurlen, T. J . Znst. Metals 89, 273 (April 1961). (39) Jaffee R . I., Maykuth, D. J., Douglas, R . W., in “Refractory Metals and Alloys,” Met. SOC. AIME, Vol. 11, p 383, Interscience, New York, 1961. (40) Kass, S., CorroJron 17, 566t (December 1961). (41) Kass, S., Scott, D. B., J . Electrochem. Soc., 109, 92 (February 1962). (42) Klopp, W. D., Krier, C. A., Defense Metals Inform. Center Memo. 88, March 3, 1961. (43) Knoerr, A., Eigo, M., Eng. Mznmg J., 162, 87 (September 1961). (44) Krier, C. A., Defense Metals Inform. Center Rept. 162, Nov. 24, 1961. (45) Kubit, C. J., Landerman, E., Tranr. A m . Nuclear Soc. 4, 91 (June 1961). (46) Leszynski, W., J . Metals 13, 746 (October 1961). (47) Lochman, J. C., M t t a l Progr. 80, 73 (July 1961). (48) Macleary, D. L., Corrosion 18, 67t (February 1962). (49) Martin, R. M., U. S. Office Tech. Services Rept. AD 258588, January 1961. (50) May, M., Haussler, G., others, Chem. Tech. 13, 281 (May 1961). (51) Michael, A. B., in “Refractory Metals and Alloys,” Met. Soc. AIME, Vol. 11, p. 357, Interscience, New York, 1961. (52) Mittenbergs, A. A., Haley, G. D., Williams, D. N., ASTM Preprint 73, 1961. (53) Mueller, C. P., in “Refractory Metals and Alloys,” Met. SOC.AIME, Vol. 11, p. 507, Interscience, New York, 1961. (54) Muller, F., Nuclear Power 6, 68 (May 1961). (55) Nettle, J. R., Hiegel, J. M., Baker,
D. H., Jr., U. S. Bur. Mines Rept. Invest. 5851, 1961. (56) Northcott, L., J . Les.r-Common Metals 3, No. 2, 125 (April 1961). (57) O’Boyle, D., Machine Design 33, 147 (Dec. 21, 1961). (58) Ogden, H. R., Perlmutter, I., Metal Progr. 80, 97 (November 1961). (59) Olofson, C. T., Boulger, F. W., Defense Metals Inform. Center Memo 134, Oct. 27, 1961. (60) Opitz, W., Tech. M i t t . 54, 311 (August 1961). (61) Osthagen, K., Kofstad, P., J. Electrochem. Soc. 109,204 (March 1962). (62) Oxley, J. H., Oberle, J. E., others, Trans. Met. SOC.AZME 221, 927 (October 1961). (63) Paprocki, S. J., Hodge, E. S., Defense Metals Inform. Center Rept. 159, Sept. 25, 1961. (64) Passmore, E. M., U. S . Office Tech. Services Rept. PB 171400, August 1960. (65) Pecker, D., Mater. Design Eng. 54, 107 (December 1961). (66) Reactor Core Materials 4, 32 (May 1961). (67) “Refractory Metals and Alloys,” Met. SOC.AIME, Vol. 11, Interscience, New York, 1961. (68) Rich, J. B., Walters, G. P., Barnes, R . S., J . Nuclear Mater. 4, 287 (AugustSeptember 1961). (69) Rostoker, W., Zbid, p. 3. (70) Rubenstein, L. S., Goodwin, J. G., Shubert, F. L., Corrosion 18, 45t (February 1962). (71) Saunders, N., U. S. Office Tech. Services Rept. AD 258265, June 1, 1961. (72) Schemel, J., Trans. M e t . Sot. A I M E 221, 1129 (December 1961). (73) Schleicher, H. W., Metalloberflache 15, 235 (August 1961). J . A m . Rocket SOC.31, (74) Scruggs, D. k.. 1527 (November 1961). (75) Sedlatschek, K., Stadler, H. J., Planseeber. Puluermet. 9, 39 (April 1961). (76) Seifert, J. W., Lower, A. L., Corrosion 17, 475t (October 1961). (77) Semchyshen, M., Barr, R . Q., Zbid., p. 283. (78) Semmel, J. W., Jr., Zbid., p. 119. (79) Sethna, D. N., Johnson, A. A., others, J . Znst. Metals 89, 476 (August 1961). (80) Sharp, C., Metalworking 18, 24 (February 1961). (81) Thompson, E. G . , Bernett, E. C.. Binder, H., Metals En,?. Quart. 1, 89 (May 1961). (82) Treco, R. M., J . Electrochem. SOC.109, 209 (March 1962). (83) Ward, W. V., Jacobson, M. I., Trans. A m . SOC. Metals 54, 84 (March 1961). (84) Waterhouse, D. F., Australasian En,gr. 52, 87 (April 1961). (85) Weisert, E. D., Metals Eng. Quart. 2, 3 (February 1962). (86) Widmer, R., Yukawa, I., Grant, N. T., Zbid., p. 183. (87) Wiederholt, W., Chem. Ind. (Diisseldorf) 13, 281 (May 1961). (88) Wilms, G . R., Rea, T. W., J . LessCommon Metals 3, No. 3, 234 (June 1961). (89) Wright, J. C., Metal Treatment and Drofi Forging 28, 153 (April 1961). (90) Young, W. R., Metals Eng. Quart. 1, 21 (November 1961). (91) Zernow, L., Lieberman, I., Mech. Eng. 83, 62 (December 1961).
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