Improved corrosion behavior of DLC-coated AZ91 Mg

Research output: Conference PapersRGC 32 - Refereed conference paper (without host publication)peer-review

View graph of relations

Detail(s)

Original languageEnglish
Publication statusPublished - Dec 2019

Conference

Title15th International Conference on Plasma Based Ion Implantation & Deposition (PBII&D 2019)
LocationSheraton Shenzhen Nanshan
PlaceChina
CityShenzhen
Period19 - 22 December 2019

Abstract

Introduction: The native film of MgO/Mg(OH)2/MgCO3 formed on the AZ91 magnesium alloy during air exposure has a porous nature and poor adhesion. It not only cannot protect the Mg substrate adequately, but also is sometimes prone to more corrosion reactions [1-3]. Deposition of a coating is an effective way to enhance the corrosion resistance and in particular, diamond like carbon (DLC) coatings can produce excellent protection and performance due to the low friction and chemical inertness. In some cases, doping with extraneous elements has been observed to enhance the corrosion resistance of DLC coatings and the properties depend on the deposition technique and precursors [4-5]. In this work, we aim at improving the corrosion resistance and adhesion strength of DLC coatings by producing an intermediate layer before DLC deposition by nitrogen plasma immersion ion implantation and deposition (N-PIII&D). 
Materials and Methods: To enhance the adhesion strength of the DLC coating,a titanium intermediate layer was deposited on the N-PIII treated AZ91 alloy substrate by medium-frequency magnetron sputtering at 250 °C in the PIII&D instrument. Afterwards, a conductive DLC layer was deposited with the aid of an anode layer ion source using an Ar to C2H2 ratio of 1 to 5 for 3 h.The phase, structure, chemical composition, and morphology were evaluated by X-ray diffraction (XRD) and atomic force microscopy (AFM). The corrosion resistance was assessed by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization conducted in simulated body fluids (SBF) at 37 °C. 
Results and Discussion: The DLC coating offers better corrosion protection. A uniform of magnesium nitride phase is produced between the DLC coating and ductile AZ91 alloy. The broad (111) XRD peak suggests a nanostructured DLC coating on the N-PIII&D AZ91 alloy (Fig. 1). The DLC coating also acts as an insulating layer to inhibit corrosion reactions between the AZ91alloy and SBF as indicated by the smaller corrosion current density and positive shift in the corrosion potential (Fig. 2). 
Conclusion: A nanostructured DLC coating decreases the corrosion current density and shifts the corrosion potential positively indicating enhanced corrosion resistance of the N-PIII treated AZ91 alloy. In conjunction with the DLC film, the ceramic layer composed of magnesium nitride improves the adhesion of the DLC coating in addition to better corrosion resistance, lower friction coefficient, and higher surface hardness thus improving the durability and longevity of the AZ91 Mg alloy.

Research Area(s)

  • Nanostructured DLC coating, AZ91 alloy, Corrosion behavior

Citation Format(s)

Improved corrosion behavior of DLC-coated AZ91 Mg. / Shanaghi, Ali; Qasim, Abdul Mateen; Mehrjou, Babak et al.
2019. Paper presented at 15th International Conference on Plasma Based Ion Implantation & Deposition (PBII&D 2019), Shenzhen, China.

Research output: Conference PapersRGC 32 - Refereed conference paper (without host publication)peer-review