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Cosintering of powder injection molding parts made from ultrafine WC-Co and 316L stainless steel powders for fabrication of novel composite structures

Simchi, A ; Sharif University of Technology

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  1. Type of Document: Article
  2. DOI: 10.1007/s11661-009-0045-5
  3. Abstract:
  4. Sintering response and phase formation during sintering of WC-Co/316L stainless steel composites produced by assembling of powder injection molding (PIM) parts were studied. It is shown that during cosintering a significant mismatch strain (>4 pct) is developed in the temperature range of 1080 °C to 1350 °C. This mismatch strain induces biaxial stresses at the interface, leading to interface delamination. Experimental results revealed that sintering at a heating rate of 20 K/min could be used to decrease the mismatch strain to <2 pct. Meanwhile, WC is decomposed at the contact area and the diffusion of C and Co into the iron lattice results in the formation of a liquid and MC and M6C carbides at 1220 °C. Spreading of the liquid accelerates the reaction, affecting the dimensional stability of the PIM parts. To prevent the reaction, surface oxidation of the cemented carbide followed by hydrogen reduction during sintering was examined. Although the amount of mismatch strain increased, formation of a metallic interface consisting of a W-Co alloy (45 to 50 at. pct Co) and a Co-rich iron alloy (18 at. pct Co) prevented the decomposition of WC and melt formation. It is also shown that the deposition of a thin Ni layer after thermal debinding decreases the mismatch stresses through melt formation, although interlayer diffusion causes pore-band formation close to the steel part
  5. Keywords:
  6. 316L stainless steel powder ; Band formations ; Biaxial stress ; Cemented carbides ; Co-sintering ; Contact areas ; Hydrogen reduction ; Interface delamination ; Interlayer diffusion ; Iron lattice ; Melt formation ; Metallic interfaces ; Mismatch strain ; Mismatch stress ; Phase formations ; Powder injection molding ; Steel parts ; Surface oxidations ; Temperature range ; Thermal debinding ; Ultra-fine WC ; Dimensional stability ; Injection molding ; Intermodulation ; Intermodulation measurement ; Iron ; Liquids ; Martensitic stainless steel ; Phase interfaces ; Plastic molds ; Powder metallurgy ; Sintering ; Structure (composition) ; Surface reactions ; Tungsten carbide ; Stainless steel
  7. Source: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 41, Issue 1 , 2010 , Pages 233-241 ; 10735623 (ISSN)
  8. URL: http://link.springer.com/article/10.1007%2Fs11661-009-0045-5