DLC and DLC-WS2 Coatings for Machining of Aluminium Alloys

Tomasz Brzezinka,Jose Paiva,Joern Kohlscheen,Jose Endrino,Jeff Rao,Stephen Veldhuis,German Fox-Rabinovich

doi:10.3390/coatings9030192

Tomasz Brzezinka, Jose Paiva + Show 5 more

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https://doi.org/10.3390/coatings9030192

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Abstract

Machine-tool life is one limiting factor affecting productivity. The requirement for wear-resistant materials for cutting tools to increase their longevity is therefore critical. Titanium diboride (TiB2) coated cutting tools have been successfully employed for machining of AlSi alloys widely used in the automotive industry. This paper presents a methodological approach to improving the self-lubricating properties within the cutting zone of a tungsten carbide milling insert precoated with TiB2, thereby increasing the operational life of the tool. A unique hybrid Physical Vapor Deposition (PVD) system was used in this study, allowing diamond-like carbon (DLC) to be deposited by filtered cathodic vacuum arc (FCVA) while PVD magnetron sputtering was employed to deposit WS2. A series of ~100-nm monolayer DLC coatings were prepared at a negative bias voltage ranging between −50 and −200 V, along with multilayered DLC-WS2 coatings (total thickness ~500 nm) with varying number of layers (two to 24 in total). The wear rate of the coated milling inserts was investigated by measuring the flank wear during face milling of an Al-10Si. It was ascertained that employing monolayer DLC coating reduced the coated tool wear rate by ~85% compared to a TiB2 benchmark. Combining DLC with WS2 as a multilayered coating further improved tool life. The best tribological properties were found for a two-layer DLC-WS2 coating which decreased wear rate by ~75% compared to TiB2, with a measured coefficient of friction of 0.05.

Highlights

Cutting, called machining, is one of the oldest methods of metalworking, comprising three main processes: surface plastic deformation, fracture and chip removal [1]
The cross-sectional images of the coatings prepared using focused ion beam (FIB) are presented in Figure 2, and the summary of the main properties of the coatings are presented in Tables 2 and 3
The substrate bias during the diamond-like carbon (DLC) deposition was found to have a significant influence on the cutting performance of the tools

Summary

Introduction

Called machining, is one of the oldest methods of metalworking, comprising three main processes: surface plastic deformation, fracture and chip removal [1]. Tool wear is obviously associated with any cutting process, though it is a complicated phenomenon; when a chip leaves the cutting zone, it carries with it a small number of particles from the worn tool. This causes a progressive change in the tool’s cutting edge profile over time, reducing the efficiency of the tool [1]. Machining lightweight alloys, such as aluminium with its high degree of plasticity, leads to what we term a built-up edge (BUE), which affects tool lifetime [2] by adhering to the cutting edge, changing its geometry and increasing the cutting forces required. BUE significantly increases wear of carbide tools due Coatings 2019, 9, 192; doi:10.3390/coatings9030192 www.mdpi.com/journal/coatings

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