Abstract
Diamond-like Carbon (DLC) coatings have attracted significant attention due to their low friction coefficient, high degree of hardness, chemical inertness, and high wear resistance as well as and their many possible uses in metallurgical, aeronautical, and biomedical applications. However, DLC has low adhesion strength to metallic substrates. Carbonitriding was performed before DLC deposition to improve this adherence. Different concentration of nitrogen in the gas mixture was used during the carbonitriding of Ti6Al4V alloy. DLC films were subsequently grown from methane using plasma enhanced chemical vapor deposition. The samples were characterized with Raman scattering spectroscopy, nanoindentation, and tribological tests. Films from 80.0% N2 had the best friction coefficient (0.07) and a critical load of ~22 N. In the scratching test, these films had adhesive failure and they completely detached from the substrate only in the end of the tests. SEM images show carbonitring promoted a significant increase in the surface defects (homogeneously distributed) but without the presence of microcracks. EDX analysis indicated that nitrogen element was diffused throughout the thickness of the samples. Hydrogen and carbon atoms from carbonitriding formed a diffusion-barrier layer that can be used as the first step for DLC deposition. This carbonitriding can also provide a carbide layer, which serves as the precursor for the nucleation and growth of DLC films.
Highlights
Many attempts have been made to achieve good adherence between diamond-like carbon (DLC) films and titanium alloys, because these films have a wide range of applications
Different concentration of nitrogen in the gas mixture was used during the carbonitriding of Ti6Al4V alloy
This study investigated the influence of nitrogen concentration, in the gas mixture, during the carbonitriding of Ti6Al4V alloy
Summary
Many attempts have been made to achieve good adherence between diamond-like carbon (DLC) films and titanium alloys, because these films have a wide range of applications. Characterized by low friction coefficient, high wear resistance, and high hardness, the use of DLC coatings in mechanical and electrical applications has increased with recent uses in food, beverage, and medical devices [1,2,3]. Different methods have been proposed by many research groups [4,5] These methods reduce the residual stress and increase the adhesion of DLC coatings [2]. Plasma nitriding has been performed to increase the surface hardness and wear resistance of austenitic stainless steel [10,11]. The carbonitriding process, a combination of carburizing and nitriding, is an efficient plasma treatment used to improve the hardness of 316 stainless steel [10].
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