A novel recycling technology for the production of bulk WC-Co hardmetals from a mixture of WO3, CoWO4 and graphite powders by way of carbothermal reduction in combination with reactive sintering has been developed. Waste hardmetals parts with 15 wt% Co from hardmetals production were fully oxidized into a mixture of WO3 and CoWO4 powder. To oxide powder mixtures, carbon was added in the form of nanocrystalline graphite, milled, pressed into compacts and sintered. During reactive sintering carbothermal reduction, tungsten monocarbide (WC) synthesis and structure formation occurs in one cycle. The influence of different graphite content in the initial powder mixtures on the phase composition, and linear shrinkage during solid and liquid state sintering is discussed. The microstructure of reactive sintered WC-Co composites is fine-grained and identical to that of the original WC-Co microstructure and has similar mechanical properties.
1. Venkateswaran, S., Schubert, W. D., Lux, B., Ostermann, M. and Kieffer, B. W-scrap recycling by the melt bath technique. Int. J. Refr. Met. Hard Mater., 1996, 14, 263–270.
http://dx.doi.org/10.1016/0263-4368(95)00055-0
2. Lux, B. Recycling of tungsten scrap by a melt bath technique. Met. Powder Rep., 1997, 51, 35.
http://dx.doi.org/10.1016/S0026-0657(97)80099-9
3. Jing-Chie Lin, J. C., Jain-Yuan Lin, J. Y. and Shie-Peir Jou, S. P. Selective dissolution of the cobalt binder from scraps of cemented tungsten carbide in acids containing additives. Hydrometallurgy, 1996, 43, 47–61.
http://dx.doi.org/10.1016/0304-386X(96)00023-0
4. Kojima, T., Shimizu, T., Sasai, R. and Itoh, H. Recycling process of WC-Co cermets by hydrothermal treatment. J. Mater. Sci., 2005, 40, 5167–5172.
http://dx.doi.org/10.1007/s10853-005-4407-0
5. Gao, N., Inagaki, F., Sasai, R., Itoh, H. and Watari, K. Resource recovery of WC-Co cermet using hydrothermal oxidation technique. Key Eng. Mater., 2005, 280–283, 1479–1484.
http://dx.doi.org/10.4028/www.scientific.net/KEM.280-283.1479
6. Lee, G. G. and Ha, G. H. Synthesis of WC/Co composite powder from waste WC/Co hard metal alloy. In Proc. Euro PM2004. Vienna, 2004, vol. 3, 403–409.
7. Shi, X., Yang, H., Shao, G., Duan, X. and Wang, S. Oxidation of ultrafine cemented carbide prepared from nanocrystalline WC-10Co composite powder. Ceram. Int., 2008, 34, 2043–2049.
http://dx.doi.org/10.1016/j.ceramint.2007.07.029
8. Upadhyaya, G. S. Cemented Tungsten Carbides: Production, Properties, and Testing. Noyes Publ.,Westwood, New Jersey, 1998.
9. Yamamoto, Y., Mizukami, M. and Matsumoto, A. Creation of nano-sized tungsten carbide powder by direct carburization. In Proc. 16th International Plansee Seminar, 2005, vol. 2, 492–505.
10. Yamamoto, Y., Matsumoto, A. and Doi, Y. Properties of ultrafine tungsten carbide and cemented carbide by direct carburization. In Proc. 14th International Plansee Seminar, 1997, vol. 2, 596–608.
11. Asada, N., Yamamoto, Y., Shimatani, K., Honkawa, S. and Miyake, M. Particle size of fine grain WC by the ‘continuous direct carburizing process’. Met. Powder Rep., 1990, 45, 60–64.
http://dx.doi.org/10.1016/S0026-0657(10)80020-7
12. Yamamoto, Y., Matsumoto, A., Honkawa, S. and Sigaki, N. A morphological study of ultrafine grain formation on reduction and direct carburizing process of tungsten oxide. In Proc. 1993 Powder Metallurgy World Congress, Kyoto, 1993, vol. 2, 785–788.
13. Vanables, D. S. and Brown, M. E. Reduction of tungsten oxides with carbon. Part 1: Thermal analyses. Thermochim. Acta, 1996, 282/283, 251–264.
http://dx.doi.org/10.1016/0040-6031(95)02814-5
14. Vanables, D. S. and Brown, M. E. Reduction of tungsten oxides with hydrogen and with hydrogen and carbon. Thermochim. Acta, 1996, 285, 361–382.
http://dx.doi.org/10.1016/0040-6031(96)02951-6
15. Ushijima, K. Production of WC Powder from WO3 with Added Co3 O4. Japan Met. Soc. Journal, 1978, 42, 871–875.
16. Takatsu, S. A new continuous process for production of WC-Co mixed powder by rotary kilns. Powder Met. Int., 1978, 10, 13–15.
17. Liu, W., Song, X., Zhang, J., Zhang, G. and Liu, X. Preparation of ultrafine WC-Co composite powder by in situ reduction and carbonization reactions. Int. J. Refr. Met. Hard Mater., 2009, 27, 115–121.
http://dx.doi.org/10.1016/j.ijrmhm.2008.05.001
18. Liu, W., Song, X., Zhang, J., Zhang, G. and Liu, X. Thermodynamic analysis for in situ synthesis of WC-Co composite powder from metal oxides. Mater. Chem. Phys., 2008, 109, 235–240.
http://dx.doi.org/10.1016/j.matchemphys.2007.11.020
19. Liu, W., Song, X., Wang, K., Zhang, J., Zhang, G. and Liu, X. A novel rapid route for synthesizing WC-Co bulk by in situ reactions in spark plasma sintering. Mater. Sci. Eng. A, 2009, 499, 476–481.
http://dx.doi.org/10.1016/j.msea.2008.09.007
20. Joost, R., Pirso, J. and Viljus, M. The structure and properties of recycled hardmetals. In Proc. 17th International Plansee Seminar, 2009, vol. 2, HM25/1–HM25/7.
21. Pirso, J., Viljus, M., Letunovitš, S. and Juhani, K. Reactive carburizing sintering: A novel production method for high quality chromium carbide-nickel cermets. Int. J. Refr. Met. Hard Mater., 2006, 24, 263–270.
http://dx.doi.org/10.1016/j.ijrmhm.2005.06.002
22. Meissl, C., Edtmaier, C., Schubert, W. D., Schön, A., Bock, A. and Zeiler, B. Sintering of tungsten carbide – cobalt composite powders. In Proc. 16th International Plansee Seminar, 2005, vol. 2, 631–640.
23. Ahn, J. H. and Kim, Y. Activated and/or liquid phase sintering of mechanically milled nanocrystalline powder. J. Metastable Nanocrystall. Mater., 1999, 2–6, 147–152.
http://dx.doi.org/10.4028/www.scientific.net/JMNM.2-6.147
24. Meredith, B. and Milner, D. R. Densification mechanisms in the tungsten carbide-cobalt system. Powder Metall., 1976, 19, 38–45.
25. Carroll, D. F. Sintering and microstructural development in WC-Co-based alloys made with superfine WC powder. Int. J. Refr. Met. Hard Mater., 1999, 17, 123–132.
http://dx.doi.org/10.1016/S0263-4368(98)00073-0
26. Im, H. S., Hur, J. M. and Lee, W. J. A study of reduced and carburized reactions in dry-milled WO3+Co3O4+C mixed powders with different carbon content. Mater. Sci. Forum, 2007, 534–536, 1149–1152.
http://dx.doi.org/10.4028/www.scientific.net/MSF.534-536.1149
http://dx.doi.org/10.4028/www.scientific.net/MSF.534-536.1185
