An Experimental Study on Nano-Carbon Films as an Anti-Wear Protection for Drilling Tools

Camelia Popescu,Doina Craciun,Liviu Duta,Bogdan Bita,Catalin Luculescu,Rodica Cristescu,Georgiana Chioibasu,Daniel Cristea,Andrei Popescu,Irina Paun

doi:10.3390/coatings7120228

Abstract

Carbon thin films of 50–100 nm thickness were synthesized by Pulsed Laser Deposition in vacuum at different laser fluences from 2 to 6 J/cm2. The deposited films were characterized by Raman spectroscopy for compositional assessment, scanning electron microscopy for morphology/thickness evaluations, and X-ray reflectivity for density, thickness, and roughness determinations. The films were ~100 nm thin, smooth, droplet-free, made of a-C:H type of diamond-like carbon. The mechanical properties of synthesized films were studied by nanoindentation and adhesion tests. The films that were obtained at low laser fluences (2, 3 J/cm2) had better mechanical properties as compared to those synthesized at higher fluences. The mean values of hardness were around 20 GPa, while the friction coefficient was 0.06. The deposition conditions of carbon thin films that displayed the best mechanical properties were further used to coat commercial drills. Both uncoated and coated drills were tested on plates that were made of three types of steel: Stainless steel 304, general use AISI 572 Gr 65 steel (OL60), and AISI D3 tool steel (C120). All of the drill edges and tips were studied by optical and scanning electron microscopes. The coated samples were clearly found to be more resistant, and displayed less morphological defects than their uncoated counterparts when drilling stainless steel and OL60 plates. In the case of C120 steel, carbon coatings failed because of the high friction between drill and the metal plate resulting in tip edges blunting that occurred during processing.

Highlights

Diamond-like carbon (DLC) is a form of carbon that lacks order at large scale, but displays crystalline structure at the nanoscale level [1]
In case of carbon films, this morphology was expected, as spherical droplets are mainly caused by the liquid phase expulsion from the target surface during irradiation, as a result of blast waves, hydrodynamic instabilities, or subsurface melting [21]
Coatings 2017, 7, 228 when inspected by Raman Spectroscopy. They were most 4 of to be of graphitic nature probably solid particles thatsurface were that ripped from the target surface and further propelled towards the substrate during proved to be of graphitic nature when inspected by Raman Spectroscopy

Summary

Introduction

Diamond-like carbon (DLC) is a form of carbon that lacks order at large scale, but displays crystalline structure at the nanoscale level [1]. In the ideal case of single bonds between carbon atoms (sp hybridization), the structure will have similar mechanical properties to those of diamond [2]. DLC contains a mix of single and double bonds, and the ratio of sp3 /sp hybridized carbon atoms dictates the mechanical behavior of this material [3,4]. Thicker DLC coatings have better mechanical properties than thinner films with the same structure, since the scratch and wear resistance are higher [12]. Thick (micrometer) DLC coatings are susceptible to delamination and may require a buffer layer to enhance their adhesion to the metallic surface [6]

Results

Discussion

Conclusion