Abstract
The research presented in this article concerns Zr–C gradient coatings that were deposited on HS6-5-2 steel by reactive magnetron sputtering from the Zr target in appropriately programmed C2H2 mass flow rate, resulting in various profiles of atomic carbon concentrations in the coating and consequently in spatial change of the properties (H, E, …) and behavior (H/E, H3/E2, We). In particular, the characteristic changes in hardness and Young’s modulus in the Zr–C coatings represented approximately by the bell curve, which has a maximum at the content of about 50 at.% C, were an inspiration to study the behavior of gradient coatings with carbon content in the range of 0–50 and 50–85 at.% with the same hardness change profile. The obtained results indicate that, firstly, the gradient of spatial changes in the coating composition increases their resistance to cohesive damage in comparison to non-gradient coatings, and, secondly, the results show that high hardness is a desired property but not sufficient to ensure adequate coating performance. Independently, an appropriate nano/microstructural structure is necessary, which determines their tribological behavior. In particular, in the case of the tested Zr–C coatings, the obtained results indicate that gradient coatings with a carbon content in the range of 50–85 at.% have better properties, characterized by the critical force Lc2, wear, coefficient of friction, H/E and H3/E2 ratios.
Highlights
Transition metal carbide coatings, including zirconium carbide coatings, have a wide range of interesting physicochemical properties, which make them attractive for a variety of applications.The strong covalent bond between Zr and C results, inter alia, in a high melting point above 3500 ◦ C, which, combined with relatively high hardness and excellent mechanical stability, enables their use in various extreme conditions [1]
The aim for the present study is to investigate the possibility of using changes in the mechanical properties of Zr–C coatings, depending on the carbon content, to produce gradient coatings characterized by increased anti-wear properties
In order to qualitatively verify the profiles of hardness changes in the coatings, surface hardness was measured with three different maximum loads, resulting in indentation depths of 0.15, 0.3 and
Summary
Transition metal carbide coatings, including zirconium carbide coatings, have a wide range of interesting physicochemical properties, which make them attractive for a variety of applications.The strong covalent bond between Zr and C results, inter alia, in a high melting point above 3500 ◦ C, which, combined with relatively high hardness and excellent mechanical stability, enables their use in various extreme conditions [1]. Zr–C-based coatings can be used for aerospace applications and for fuel particles in nuclear reactions [2]. Zr–C coatings are considered for biomedical applications to improve the corrosion resistance and hemocompatibility of implant materials [4] or NiTi shape memory alloys [5,6,7]. The presented examples of applications of Zr–C-based coatings and the prospects for new applications of these coatings, resulting from the high potential of shaping their properties, inspire research work aimed at establishing the correlation between the nano/micro structure and properties of coatings [8,9,10,11,12,13,14]. In this field, one of the research topics is the analysis of changes in the properties of the coatings along with the increase in the total carbon content in Coatings 2020, 10, 1121; doi:10.3390/coatings10111121 www.mdpi.com/journal/coatings
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