Improving the Properties of Composite Titanium Nitride Layers on the AZ91D Magnesium Alloy Using Hydrothermal Treatment.

Krzysztof Rożniatowski,Janusz Kamiński,Rafał Jakieła,Paweł Marchlewski,Tadeusz Wierzchoń,Michał Tacikowski,Marcin Pisarek

doi:10.3390/ma14195903

Abstract

Coating magnesium alloys with nitride surface layers is a prospective way of improving their intrinsically poor surface properties; in particular, their tribological and corrosion resistance. These layers are usually produced using PVD methods using magnetron sputtering or arc evaporation. Even though the thus-produced layers significantly increase the wear resistance of the alloys, their effects on corrosion resistance are unsatisfactory because of the poor tightness, characteristic of PVD-produced products. Tightness acquires crucial significance when the substrate is a highly-active magnesium alloy, hence our idea to tighten the layers by subjecting them to a post-deposition chemical-hydrothermal-type treatment. This paper presents the results of our experiments with a new hybrid surface engineering method, using a final tightening pressure hydrothermal gas treatment in overheated steam of the composite titanium nitride layers PVD, produced on AZ91D magnesium alloy. The proposed method resulted in an outstanding improvement of the performance properties, in particular resistance to corrosion and wear, yielding values that exceed those exhibited by commercially anodized alloys and austenitic stainless 316L steel. The developed hybrid method produces new, high-performance corrosion and wear resistant, lightweight magnesium base materials, suitable for heavy duty applications.

Highlights

The aim of the present work was to improve the durability of protective nitride surface layers on magnesium alloys using a recently developed, novel surface engineering hybrid method, based on the concept of a final tightening of layers using pressure hydrothermal gas treatment [1], to produce corrosion and wear resistant composite lightweight magnesium base material
Neither of the sub-layers exhibited any visible discontinuities. These layers, which diffusively bound with the magnesium alloy, as shown by our earlier research [22], demonstrated good adhesion to the substrate and the absence of macroscopic defects or cross-layer discontinuities
The layers exhibited a surface morphology that is typical for the arc evaporation method used for the deposition of the outer titanium nitride, with characteristic defects, such as the so-called droplets and craters left after droplet decohesion (Figure 3), with craters being relatively shallow (Figure 2) and limited to the outside titanium nitride layer [21]

Summary

Introduction

The aim of the present work was to improve the durability of protective nitride surface layers on magnesium alloys using a recently developed, novel surface engineering hybrid method, based on the concept of a final tightening of layers using pressure hydrothermal gas treatment [1], to produce corrosion and wear resistant composite lightweight magnesium base material. This becomes especially important in the context of the growing interest in a much wider use for light alloys in modern technology, especially the lightest of the metallic structural materials: magnesium alloys (~1.8 g/cm ). Given the high chemical activity of magnesium, simultaneous mechanical and wear resistance is essential to ensure durability in heavy duty applications

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