The effect of carbon doping on microstructure, mechanical properties, wear resistance and cutting performance of AlTiCN coating

Highlights

• Preparation of AlTiCN coatings by adding carbon element in target.

• The doped carbon acts as a growth inhibitor in the coating.

• When the carbon content is 0.2 at.%, amorphous domains appear in the coating.

• As the carbon content increases, the wear resistance is significantly improved.

Abstract

A series of AlTiCN coatings with different carbon contents (0–0.7 at.%) were deposited on YG10 (WC + 10 wt.% Co) cemented carbide by cathodic arc-evaporation of Ti-Al/Ti-Al-C targets in a mixture of Ar and N₂ gases. The influence of carbon doping on microstructure, mechanical properties, wear resistance and cutting performance was systematically investigated by comparing carbon-free coating and coatings with different carbon contents. The microstructure of the coatings has been changed significantly with the addition of C, and the amorphous domains appear when the doping amount of C is among 0.2–0.5 at.%. Instead of forming bonds with other elements in the coating, carbon only acts as a growth inhibitor. When the carbon content is 0.2 at.%, the hardness of the coating significantly decreased, but changes a little with the carbon content continue to rise. The addition of C significantly improves the wear resistance of the coating, which is mainly attributed to the transformation of the crystalline state and the formation of the dense Al₂O₃ oxide layer. Among them, the coating with a carbon content of 0.2 at.% has both excellent wear resistance and cutting performance.

Introduction

As one of the most studied hard coating systems to date, AlTiN has attracted the attention of many researchers. AlTiN coating is superior to traditional TiN in hardness and wear resistance, and the addition of Al also greatly improves the high temperature resistance of the coating [1], [2], [3], [4]. AlTiN coating prepared by physical vapor deposition (PVD) has been widely used in various industrial fields, especially as protective material, such as cutting tools and friction parts [5], [6], [7]. Cathodic arc evaporation is one of the most commonly used techniques for preparing nitride coating. The coating prepared by cathodic arc evaporation usually has a relatively dense structure and good thermal stability. However, since the surface diffusion capacity of deposited particles is high, droplet defects are often formed on the coating surface, which improves the surface roughness of the coating [8].

At present, with the continuous development of technologies in the field of processing, the requirements for coating performance are gradually becoming higher, and the traditional AlTiN coating has been difficult to meet the needs of most industries [9], [10], [11], [12]. Therefore, how to prepare nitride coatings with better properties has gradually become a trend of current research. The properties of AlTiN coatings have been improved by element doping and residual stress controlling in recent years [13], [14]. Many researchers have carried out research on alloying modified nitride coatings. Aninat et al. [15] reported how the addition of Y, Ta or Y and Ta affects the structural and mechanical properties of Ti-Al-N, which were deposited by industrial cathodic arc evaporation system. Danek et al. [16] prepared TiAlN/CrAlN coatings with different Cr concentrations by DC reactive magnetron sputtering to investigate the effects of Cr on structure, mechanical properties and oxidation properties at 800 and 900^°C.

Among them, carbon atoms can exist in coatings in various forms (such as crystal compounds or a-carbon), and different coating structures exhibit different properties with the change of carbon content [17,18]. Many researches have shown that when carbon content is in a low range (<7 at.%), the addition of carbon can increase the hardness of AlTiN coating, but as the content continues to increase, the hardness of coating decreases instead [19], [20], [21]. However, there is still a lack of systematic research on the relationship between microstructure and properties of coatings with low carbon content. In addition, many researchers doped C mainly through the reaction atmosphere (such as methane, acetylene and other gases), which brought safety risks to production. It's a good choice to use binary or even ternary alloy targets to prepare coatings with different elements. Yin et al. [22] prepared AlTiSiN and AlTiBN coatings by cathode arc evaporation using ternary AlTiSi and AlTiB alloy targets. The prepared AlTiSiN and AlTiBN coatings have higher hardness and lower wear rate than AlTiN.

Therefore, based on the above two points, this paper proposes to prepare carbon-doping AlTiN coatings by adding 2 at.% carbon to the target source by using cathodic evaporation deposition. The content of carbon in the coatings was adjusted by controlling the proportion of two different targets (Ti-Al/Ti-Al-0.2C) in the deposition process, and the microstructure and related properties of the coating are studied to find the best carbon doping amount.