Tailored Mechanical Properties and Residual Stresses of a-C:H:W Coatings

Christoph Schmid,Stephan Tremmel,Harald Hetzner,Felix Hilpert,Karsten Durst

doi:10.4028/www.scientific.net/amr.996.14

Christoph Schmid, Stephan Tremmel + Show 3 more

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https://doi.org/10.4028/www.scientific.net/amr.996.14

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Abstract

In this study, three different a-C:H:W coatings with predefined hardness values, ranging from 10 up to 16 GPa, were deposited by adjusting bias voltage according to a previously created regression model. For this purpose, the influence of the main process parameters of the used reactive unbalanced magnetron sputtering process on the mechanical properties of the a-C:H:W coating was investigated previously by nanoindentation. For a systematical evaluation of the single effects, parameters were varied according to a central composite design. The three coating variants of this study were investigated in terms of microstructure, mechanical properties and residual stresses. It turned out, that by the use of the regression model, a-C:H:W coatings with tailored mechanical properties can be deposited. Residual stresses were measured by means of focused ion beam milling of a double-slit geometry, which causes the internal stresses to relax, and mapping of the resultant relief strain by digital image correlation. A linear relation between the applied bias voltage and the hardness, the modulus of the coating as well as the determined relief strain was observed. Thus, residual stresses of the coatings increase disproportionately with applied bias voltage. The obtained results can be helpful for tailored coating design and further optimization of a-C:H:W coatings.

Highlights

Residual stresses were measured by means of focused ion beam milling of a double-slit geometry, which causes the internal stresses to relax, and mapping of the resultant relief strain by digital image correlation
Amorphous carbon coatings are well known for their beneficial properties such as high hardness combined with low coefficients of friction, chemical inertness and high wear-resistance [1]
With adjusting the deposition time according to the regression model, the thickness of the different amorphous carbon (a-C):H:W layers is equal

Summary

Introduction

Amorphous carbon coatings are well known for their beneficial properties such as high hardness combined with low coefficients of friction, chemical inertness and high wear-resistance [1] These coatings frequently suffer from high internal stresses and show poor adhesion to many technical relevant substrates like steel, limiting their fields of application. Amorphous carbon coatings, such as hydrogenated amorphous carbon (a-C:H), can be doped with transition metals to modify specific properties [5] In this context, one major advantage of metal modified hydrogenated amorphous carbon (a-C:H:Me) coatings is the reduced internal stresses and the associated enhanced effective adhesion of the coatings to the substrate [6, 7]. The probably most common type of a-C:H:Me is tungsten modified hydrogenated amorphous carbon (a-C:H:W)

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