TiN coating on an electrical discharge machined WC-Co hardmetal: surface integrity effects on indentation adhesion response |
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Authors: | B Casas M Anglada V K Sarin L Llanes |
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Affiliation: | (1) Dept. de Ciència dels Materials i Enginyería Metal.lúrgica, ETSEIB, Universitat Politècnica de Catalunya, E-08028 Barcelona, Spain;(2) Department of Manufacturing Engineering, College of Engineering, Boston University, Boston, MA 02215, USA |
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Abstract: | Electrical discharge machining (EDM) is an alternative-shaping route for manufacturing complex component shapes of hard and
brittle materials such as hardmetals (WC-Co cemented carbides). It is well established that in these materials EDM typically
induces a heat affected surface layer with poor integrity. This degradation effect may be compensated through specific post-EDM
surface treatments either by thermomechanical means or material surface deposition. In the latter case, a key property for
optimal performance is the level of coating to substrate adhesion and how this is affected by the EDM-induced surface. The
main objective of this investigation was to evaluate the adhesion strength of TiN coatings on EDMed hardmetals. A series of
hardmetal samples that had been subjected to different multi-pass sequential EDM levels were coated with TiN. Adhesion behavior
was assessed using the indentation adhesion test and comparing the critical load for crack extension (P
c) and the interfacial fracture toughness (K
Ic,interface) to those exhibited by the TiN coating deposited on a ground and polished substrate (used as baseline control). Experimental
results indicated that indentation adhesion increased with finer-executed EDM, almost reaching baseline level values. The
results are discussed on the basis of the compromising EDM influence on both surface integrity of the substrate and tortuousness
at the interface, the latter resulting in mechanical anchoring of the TiN coating to the hardmetal substrate. |
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