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MICROSTRUCTURAL EFFECTS ON THE MECHANICAL INTEGRITY OF ELECTRICAL-DISCHARGE-MACHINED 113

  • : Fernando García-Marro1, Alvaro Mestra1, Giselle Ramirez2, Montserrat Vilaseca2, Jose Antonio Calero3, Daniel Casellas2, Luis Llanes1
  • : 1Universitat Politècnica de Catalunya, 2CTM Centre Tecnològic de Manresa, 3AMES
  • : PDF Download
  • : 2014

Abstract

Electrical discharge machining (EDM) has proven to be satisfactory in shaping hardmetals (WC-Co cemented carbides). However, it is also known that surface integrity of EDMed hardmetals may be degraded, in terms of induced surface flaws as well as residual stresses, corresponding relevance being dependent upon microstructure of the grades under consideration. In this work, two microstructurally different WC-Co cemented carbides have been studied: one “harder” fine-grained and another “tougher” medium-grained one. It is found that mechanical strength of hardmetals may be strongly affected by EDM, depending on the effective damage tolerance of the grade under consideration. Within this context, the residual strength of EDMed cemented carbides results from the compromising effect of fracture toughness, relatively length scale of processing flaws and EDM-induced defects, and developed tensile residual stresses. Moreover, post-EDM thermal treatments at temperatures between 920 and 1120 ºC are shown to be helpful for partial recovery of the strength exhibited by the reference surface condition, i.e. ground and polished. This is particularly true for the tougher and coarser hardmetal grade.
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