Morphological and microstructural characterization of nanostructured pure α-phase W coatings on a wide thickness range

TL;DR: In this paper, the influence of the sputtering power on the adhesion of the coatings to the substrate was investigated by depositing coatings at powers varying from 30 up to 220 W.

About: This article is published in Applied Surface Science.The article was published on 2014-10-15 and is currently open access. It has received 33 citations till now. The article focuses on the topics: Coating & Sputter deposition.

Summary

1. Introduction

• Based on Thornton works, the authors aim to optimize the sputtered W coatings by tuning the sputtering parameters.
• The authors report on the DC sputtering parameters which lead to nondelaminated, pure ␣-W phase coatings.
• The dependence of sample morphology, microstructure, stress/strain state and mechanical properties as a function of thickness will be discussed.
• In addition, a preliminary study about W deposition on commercial steel substrate was performed due to the interest for possible applications in the industry.

2. Experimental procedure

• In order to evaluate the mechanical response of the coatings, nanoindentation tests were carried out by using a MTS Nanoindenter XP and the continuous stiffness measurement technique together with a diamond Berkovich indenter.
• Hardness and elastic modulus were obtained by an indentation depth of 10-15% of the coating thickness to avoid the influence of the substrate.
• These values were determined from the unloading part of the force-depth (F-d) curve according to the procedure reported in the literature [27] .

3.2.1. Morphology

• Additional information about the compactness of the coatings can be obtained from density measurements.
• The average coating density, estimated by combining RBS and SEM measurements, was calculated to be 19.50 ± 0.30 g/cm 3 .
• This density value is similar to that tabulated for pure coarse grained W (19.25 g/cm 3 ) [31] , which indicates that the authors are dealing with highly compacted coatings.

3.2.2. Microstructure

• A deeper analysis of the XRD patterns allows us to obtain more information about the film total stress and micro-strain.
• The film total stress was evaluated by analysing the centroid ␣-W{1 1 0} peak profile in comparison to that reported for the conventional W, Fig. 6(a) .
• The Hardness, Young's modulus and loaddisplacement curves for the sample deposited on steel are depicted in Fig. 9 (a) and (b), respectively, as a function of indentation depth.
• On these bases, the authors can conclude that the morphological, microstructural and mechanical properties for coatings deposited on commercial steel are comparable to those for coatings sputtered on (1 0 0) Si.

Figures

Fig. 1. Optical images of the surface for samples deposited on (1 0 0) Si at different plasma power. (a) Delamination and cracks are evident for the sample deposited at 160 W ( ross s (

Fig. 4. Dark field TEM images measured at two d

Fig. 2. Top view (left column),cross-section FEG-SEM images (middle column) and histograms (right column) representing the average column diameter on the sample surface for coatings with different thickness: (a) 250 nm (black), (b) 600 nm (red), (c) 1200 nm (green), (d) 2000 nm (dark blue), (e) 4000 nm (light blue) deposited on (1 0 0) Si and (f) 1800 nm (magenta) deposited on commercial steel substrates. The scale bar is 800 nm for all photos and the thicknesses are indicated on each image.

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In a previous work this paper, the authors have presented an overview of the relationship between the safety and Durability of Structures and Materials ( CISDEM ), UPM-CSIC, IMM-CNM, and Isaac Newton 8 PTM.