Characterization of ZrN coating low-temperature deposited on the preliminary Ar+ ions treated 2024 Al-alloy

Abstract

The present paper considers the problem of the low-temperature deposition of the hard coatings on the alloys having a low melting point and a high affinity for oxygen, like aluminum or magnesium alloys. It is demonstrated that a hard ZrN coating can be produced on the 2024 aluminum alloy by the low-temperature vacuum-arc deposition method. To achieve high adhesion strength between the coating and substrate, the substrate was sputtered by low-energy inert Ar+ ions before the deposition process in order to remove the natural oxide layer. The optimal technological regimes selected and used allowed obtaining the stoichiometric ZrN coating of extremely low roughness (0.061 μm), uniform thickness (~1 μm) with nano-scale columnar microstructure with the cross-sectional size of the columnar grains of ~20–50 nm. The layered microstructure of the obtained coating respectively consisted of the columnar and V-shaped grains in the lower and upper layers comes to be in the ‘transition zone’ on the ‘structure-zone diagram’. The lower layers consist of a number of AlxZry phases along with the Zr3N4 orthorhombic phase, while the outmost layer of the film contains the single ZrN fcc phase. In comparison with the substrate alloy, the produced ZrN coating is shown to possess the superior anti-corrosion properties in saline solution, a high hardness (~20 GPa) and elastic modulus (196 GPa), high adhesion strength both at the progressively increased load and at cyclic dry sliding of the conical diamond indenter with the 50 μm tip, low friction coefficients and high wear resistance at the reciprocating sliding both in the dry and wet (liquid paraffin) conditions against the conical diamond indenter with the 50 μm tip and 8 mm Si3N4 ball, respectively.