Effect of pretreatment strategy on the microstructure, mechanical properties and cutting performance of diamond coated hardmetal tools using HFCVD method

https://doi.org/10.1016/j.ijrmhm.2021.105687Get rights and content
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Highlights

  • CVD diamond coated hardmetal tools using pretreatment strategy, including single AMA-treatment, 500 nm thick WC interlayer sputtered only, duplex pretreatments (AMA-treated plus sputtered WC interlayer with three thicknesses.

  • Microstructure, adhesion and mechanical property evolution of diamond coatings vs pretreatment strategies are studied.

  • Different cutting performances and failure mechanisms vs pretreatment strategies are attained.

Abstract

Diamond coatings are deposited on cemented carbide (WC-Co) tools to lengthen their cutting lifetime. However, their industrial application is held back by poor diamond coating–substrate adhesive strength. In this paper, the cutting performance of differently pretreated diamond-coated WC-Co tools for graphite milling was examined. The WC and Co phases on the surface of the WC-Co substrates were treated by a three-step acid-Murakami-acid chemical etching process (AMA–treatment) followed by physical vapor deposition (PVD) of a WC interlayer with a thickness of 250, 500, or 750 nm. Finally, a multilayered coating was obtained by depositing a 4 μm thick diamond coating using hot filament chemical vapor deposition (HFCVD). The effect of this composite pretreatment on the adhesive strength and cutting performance of diamond-coated WC-Co tools were studied and compared with diamond-coated WC-Co tools only pretreated by either AMA–treatment or deposition of a 500 nm WC interlayer. Adhesive strength tests assessed by the Rockwell indentation method showed that a combination of AMA–treatment and a thinner WC interlayer (250 or 500 nm) enhanced the adhesive strength (HF1) and cutting performance of these diamond-coated WC-Co tools. SEM and EDS analyses indicated that coating delamination, fracture, diffusion, and adhesive wear were the main failure mechanisms of the cutting tools. Finally, in graphite cutting tests, the diamond-coated WC-Co tool with a composite pretreatment consisting of AMA–treatment and deposition of a 250 nm WC interlayer exhibited significantly enhanced cutting performance (VBmax = 0.18 mm at a cutting length of 200 m) compared with the other pretreated tools.

Keywords

Diamond coatings
WC interlayer
Pretreatments
WC-co
Adhesive strength
Cutting tests

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