Cobalt capping: Why is sintered hardmetal sometimes covered with binder?
Source abstract
Abstract
Abstract Some sintered hardmetal grades come out of the furnace covered with a thin layer of binder at the surface, while others do not. The layer can be beneficial for subsequent brazing, but it must be removed by grinding or etching if the hardmetal is to be coated. It would be beneficial to be able to control this “cobalt capping” during sintering by applying suitable sintering conditions. For this purpose, the mechanism of cobalt capping was investigated. The capping occurs on the cooling ramp, at the eutectic temperature of the binder. If the binder solidifies first in the interior, the contraction caused by the phase transition squeezes melt out of the exterior zones. The contraction of the specimen was verified with dilatometry. Conditions leading to cobalt capping are: higher carbon content in the surface than in the bulk (decrease of melting point), high binder content, especially in the surface zone, and a low cooling rate.
Source: openaire · Quality: candidate unverified · Source record ↗
Research context
SciVX discovery tags are terminology-based. OpenAlex topics are source-provided classifications.
References (15)
Show source-provided references
1. Tailoring hardness and toughness gradients in functional gradient hardmetals (FGHMs)10.1016/j.ijrmhm.2005.03.008 ↗
2. Formation of Co-capping during sintering of straight WC-10wt% Co10.1016/j.ijrmhm.2009.11.005 ↗
3. Tsuda K, Isobe K, Ikegaya A, Kitagawa N. Nitrogen-containing sintered alloy containing a hard phase. Patent no. 6057,046(US), 2000.
4. Rolander U, Weinl G. Sintering method for producing titanium-based carbonitride alloys free from binder phase surface layer. Patent no. WO9902746, 1999.
5. Comer CR. Process to enhance brazability of carbide bits. Patent no. US0211493, 2004.
6. Taniguchi Y, Sasaki H, Ueki M, Kobori K. Manufacture of surface-refined sintered alloy. Patent no. DE3744573, 1988.
7. Nakano M, Tobioka M, Nomura T. Coating of cutting tips from sintered hard alloys. Patent no. EP0337696, 1989.
8. Solidification of cemented carbide compositions containing excess amounts of carbon
9. Janisch DS, Lengauer W, Dreyer K, Rödiger K, van den Berg H. Can we influence hardmetal properties by sintering in carbon monoxide? In: Euro PM2008. Mannheim (D). 2008;1:225–30.
10. Effect of WC particle size on Co distribution in liquid-phase-sintered functionally graded WC–Co composite10.1016/j.ijrmhm.2007.02.003 ↗
11. Kinetics of cobalt gradient formation during the liquid phase sintering of functionally graded WC–Co10.1016/j.ijrmhm.2006.07.002 ↗
12. Sintering, characterisation, and analysis of functional gradient hardmetals10.1016/j.ijrmhm.2007.05.006 ↗
13. Hammond CR. Density of molten elements and representative salts. In: Lide DR, Lide DR, Lide DR, editors. Handbook of Chemistry and Physics. Boca Raton: CRC Press; 2004, p. 126–9 [Sec. 4].
14. Thermodynamic properties of the Co–W–C system10.1007/BF02651660 ↗
15. Janisch DS, Lengauer W, Rödiger K, Dreyer K, van den Berg H. Novel fine-grained hardmetals by use of multiphase powder precursors and reactive nitrogen sintering. Int J Refract Met Hard Mater, in press [corrected proof].