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Scratch adhesion characteristics of PVD Cr/CrAlN multilayer coating deposited on aerospace AL7075-T6 alloy

Q.M Mehran (Department of Mechanical Engineering, Faculty of Engineering and Centre of Advanced Manufacturing and Material Processing, AMMP Centre, University of Malaya, Kuala Lumpur, Malaysia)
A.R Bushroa (Department of Mechanical Engineering, Faculty of Engineering and Centre of Advanced Manufacturing and Material Processing, AMMP Centre, University of Malaya, Kuala Lumpur, Malaysia)
M.A Fazal (Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur, Malaysia)
M.M. Quazi (Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur, Malaysia)

Pigment & Resin Technology

ISSN: 0369-9420

Article publication date: 2 November 2015

286

Abstract

Purpose

The purpose of this study is to design and develop a new functional coating system for aerospace AL7075-T6 alloy that would evaluate the mechanical properties of the coating.

Design/methodology/approach

This paper outlines the scratch adhesion characterisation of Cr/CrAlN coating using a combination of radio frequency (RF) and direct current (DC) physical vapour deposition (PVD) magnetron sputtering. The surface morphology, microstructure and chemical composition of the Cr/CrAlN film were evaluated by optical microscopy (OM), field emission scanning electron microscopy (FESEM) integrated with energy-dispersive X-Ray spectroscopy (EDX) and atomic force microscopy (AFM). The film-to-substrate adhesion was measured by a scratch test machine manufactured with a detection system, motorized stages, penetration depth sensors, optical microscope and tangential frictional load sensors.

Findings

The AFM and ultra-micro hardness results showed an increase in surface roughness to about 20 per cent and hardness to about 74 per cent. Moreover, the film-to-substrate adhesion strength of 1,814 mN was obtained with PVD deposition process.

Research limitations/implications

The main limitation of this work is caused by PVD deposition process. Besides, surface defects such as pinholes contribute to a decrease in adhesion strength.

Practical implications

The higher hardness of CrAlN coating is used to improve the properties of softer aluminium substrates. This hardness prevents ploughing-induced wear and provides greater adhesion strength by preventing coating delamination.

Originality/value

Until now, CrAlN is coated only on ferrous alloys. It has not yet been tried on aluminium alloys. Moreover, coating functionality depends on higher adhesion and failure mechanisms involved in the film-to-substrate system, which is significant in aerospace applications.

Keywords

Acknowledgements

The authors acknowledge the financial support under the University Malaya Research Grant UM. TNC2/IPPP/UPGP/638/PPP/PG116-2013A from the University of Malaya, Malaysia. This research is also partially supported by UMRG (Program) grant of UM. TNC2/RC/AET/261/1/1/RP017-2012C.

Citation

Mehran, Q.M., Bushroa, A.R., Fazal, M.A. and Quazi, M.M. (2015), "Scratch adhesion characteristics of PVD Cr/CrAlN multilayer coating deposited on aerospace AL7075-T6 alloy", Pigment & Resin Technology, Vol. 44 No. 6, pp. 364-370. https://doi.org/10.1108/PRT-09-2014-0081

Publisher

:

Emerald Group Publishing Limited

Copyright © 2015, Emerald Group Publishing Limited

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