Technologies of Coatings and Surface Hardening for Tool Industry

The innovative coating and surface hardening technologies developed in recent years allow us to obtain practically any physical–mechanical or crystal–chemical complex properties of the metalworking tool surface layer. Today, the scientific approach to improving the operational characteristics of the tool surface layers produced from traditional tools industrial materials is a highly costly and long-lasting process. Different technological techniques, such as coatings (physical and chemical methods), surface hardening and alloying (chemical-thermal treatment, implantation), a combination of the listed methods, and other solutions are used for this. This edition aims to provide a review of the current state of the research and developments in the field of coatings and surface hardening technologies for cutting and die tools that can ensure a substantial increase of the work resource and reliability of the tool, an increase in productivity of machining, accuracy, and quality of the machined products, reduction in the material capacity of the production, and other important manufacturing factors. In doing so, the main emphasis should be on the results of the engineering works that have had a prosperous approbation in a laboratory or real manufacturing conditions

Recent Advances on Coated Milling Tool Technology—A Comprehensive Review

The milling process is one of the most used processes in the manufacturing industry. Milling, as a process, as evolved, with new machines and methods being employed, in order to obtain the best results consistently. Milling tools have also seen quite an evolution, from the uncoated high-speed steel tool, to the now vastly used, coated tools. Information on the use of these coated tools in recent scientific researches was collected. The coatings that are currently being researched are going to be presented, highlighting some novel advances in the nanocomposite and diamond coatings area, as these coatings are seeing a growing use in the industry, with very satisfactory results, with performance and tool-life increase. Wear mechanism of various types of coatings are also a popular topic on recent research, as the cutting behavior of these coated tools provides valuable information on the tool’s-life. Furthermore, analysis of these mechanisms enables for the selection of the best coating type for the correct application. Recently, the employment of coated tools paired with sustainable lubrication methods as seen some use. As this presents the opportunity to enhance the coated tool’s and the process’s performance, obtaining better results, in terms of better tool-life and better surface finish quality, in a more sustainable fashionThis research was funded by ON-SURF Project, grant number NUP POCI-01-0247-FEDER-024521.info:eu-repo/semantics/publishedVersio

Coatings and Surface Modification of Alloys for Tribo-Corrosion Applications

This review of the tribocorrosion of coatings and surface modifications covers nearly 195 papers and reviews that have been published in the past 15 years, as compared to only 37 works published up to 2007, which were the subject of a previous review published in 2007. It shows that the research into the subject area is vibrant and growing, to cover emerging deposition, surface modification and testing techniques as well as environmental influences and modelling developments. This growth reflects the need for machines to operate in harsh environments coupled with requirements for increased service life, lower running costs and improved safety factors. Research has also reacted to the need for multifunctional coating surfaces as well as functionally graded systems with regard to depth. The review covers a range of coating types designed for a wide range of potential applications. The emerging technologies are seen to be molten-, solution-, PVD- and PEO-based coatings, with CVD coatings being a less popular solution. There is a growing research interest in duplex surface engineering and coating systems. Surface performance shows a strong playoff between wear, friction and corrosion rates, often with antagonistic relationships and complicated interactions between multiple mechanisms at different scale lengths within tribocorrosion contacts. The tribologically induced stresses are seen to drive damage propagation and accelerate corrosion either within the coating or at the coating coating–substrate interface. This places a focus on coating defect density. The environment (such as pH, DO2, CO2, salinity and temperature) is also shown to have a strong influence on tribocorrosion performance. Coating and surface modification solutions being developed for tribocorrosion applications include a whole range of electrodeposited coatings, hard and tough coatings and high-impedance coatings such as doped diamond-like carbon. Hybrid and multilayered coatings are also being used to control damage penetration into the coating (to increase toughness) and to manage stresses. A particular focus involves the combination of various treatment techniques. The review also shows the importance of the microstructure, the active phases that are dissolved and the critical role of surface films and their composition (oxide or passive) in tribocorrosion performance which, although discovered for bulk materials, is equally applicable to coating performance. New techniques show methods for revealing the response of surfaces to tribocorrosion (i.e., scanning electrochemical microscopy). Modelling tribocorrosion has yet to embrace the full range of coatings and the fact that some coatings/environments result in reduced wear and thus are antagonistic rather than synergistic. The actual synergistic/antagonistic mechanisms are not well understood, making them difficult to model

Overview on the antimicrobial activity and biocompatibility of sputtered carbon-based coatings

Due to their outstanding properties, carbon-based structures have received much attention from the scientific community. Their applications are diverse and include use in coatings on self-lubricating systems for anti-wear situations, thin films deposited on prosthetic elements, catalysis structures, or water remediation devices. From these applications, the ones that require the most careful testing and improvement are biomedical applications. The biocompatibility and antibacterial issues of medical devices remain a concern, as several prostheses still fail after several years of implantation and biofilm formation remains a real risk to the success of a device. Sputtered deposition prevents the introduction of hazardous chemical elements during the preparation of coatings, and this technique is environmentally friendly. In addition, the mechanical properties of C-based coatings are remarkable. In this paper, the latest advances in sputtering methods and biocompatibility and antibacterial action for diamond-based carbon (DLC)-based coatings are reviewed and the greater outlook is then discussed.This research is sponsored by national funds through FCT—Fundação para a Ciência e a Tecnologia, under the projects UIDB/00285/2020, UID/EMS/00285/2019 and UIDB/04650/2020, ATRITO-0 (co-financed via FEDER (PT2020) POCI-01-545 0145-FEDER-030446) and On-SURF (cofinanced via FEDER (PT2020) POCI-01-0247-FEDER-024521). Also, this work is supported by European Regional Development Fund (ERDF), through the Centro 2020 Regional Operational Programme under project CENTRO-01-0145-FEDER-000012-HealthyAging2020, and through the COMPETE 2020—Operational Programme for Competitiveness and Internationalization and Portuguese national funds via FCT-Fundação para a Ciência e a Tecnologia, under projects POCI-01-0145-FEDER-007440 and UID/NEU/04539/2019

The critical raw materials in cutting tools for machining applications: a review

A variety of cutting tool materials are used for the contact mode mechanical machining of components under extreme conditions of stress, temperature and/or corrosion, including operations such as drilling, milling turning and so on. These demanding conditions impose a seriously high strain rate (an order of magnitude higher than forming), and this limits the useful life of cutting tools, especially single-point cutting tools. Tungsten carbide is the most popularly used cutting tool material, and unfortunately its main ingredients of W and Co are at high risk in terms of material supply and are listed among critical raw materials (CRMs) for EU, for which sustainable use should be addressed. This paper highlights the evolution and the trend of use of CRMs) in cutting tools for mechanical machining through a timely review. The focus of this review and its motivation was driven by the four following themes: (i) the discussion of newly emerging hybrid machining processes offering performance enhancements and longevity in terms of tool life (laser and cryogenic incorporation); (ii) the development and synthesis of new CRM substitutes to minimise the use of tungsten; (iii) the improvement of the recycling of worn tools; and (iv) the accelerated use of modelling and simulation to design long-lasting tools in the Industry-4.0 framework, circular economy and cyber secure manufacturing. It may be noted that the scope of this paper is not to represent a completely exhaustive document concerning cutting tools for mechanical processing, but to raise awareness and pave the way for innovative thinking on the use of critical materials in mechanical processing tools with the aim of developing smart, timely control strategies and mitigation measures to suppress the use of CRMs

Processing, microstructure and mechanical behavior of nanocomposite multilayers

Nanoscale multilayer coatings have high potential for numerous engineering applications because they can exhibit enhanced properties due to nanoscale effects and combine different properties from individual components. At present, scale effects on the mechanical behavior of multilayers are not well understood. Three multilayer nanocomposite systems, namely Al/Al2O3, Ti/TiN, and Cr/a-C, have been synthesized by using a dual-gun e-beam physical vapor deposition, to investigate the effect of layer thickness, the nature of components and their microstructures on the mechanical behavior. The deposited Al and Ti nanolayers were found to have polycrystalline fcc and hcp structure, respectively, the Cr and TiN layers had fine columnar bcc and fcc structure, respectively, and the Al2O3 and C layers were amorphous. Nanoscale effects were observed in all three systems with the metal layer thickness affecting significantly the mechanical behavior. The hardness response of the present systems can be described as a function of the metal layer thickness by a Hall-Petch relationship. A critical Al layer thickness of 40 nm, below which there was no further hardness enhancement, was found for the Al/Al2O3 multilayers. The critical Al layer thickness could be predicted by previous theoretical models. A hardness increase was observed down to a Ti layer thickness of 5 nm for the Ti/TiN system. The strengthening of the Ti/TiN multilayers was consistent with the macroyield maps based on a confined layer slip model. Hardness in the Cr/a-C system showed a continuous increase down to a Cr layer thickness of 20 nm. The fracture toughness of the monolithic ceramic phase was significantly improved by introducing a metal/ceramic multilayered structure. The wear behavior of the present multilayers was mainly controlled by the ceramic phase. The Cr/a-C multilayers achieved a low friction coefficient (~0.1) and low wear rate (~10-5 mm3/N m). The present research shows that properties can be tailored by appropriate selection of layer thickness and nature of individual components

Structural and Mechanical Properties of DLC/TiN Coatings on Carbide for Wood-Cutting Applications

In this work, the diamond-like carbon and titanium nitride (DLC/TiN) multilayer coatings were prepared on a cemented tungsten carbide substrate (WC—3 wt.% Co) using the cathodic vacuum arc physical vapor deposition (Arc-PVD) method and pulsed Arc-PVD method with a graphite cathode for the deposition of TiN and carbon layers, respectively. The structural and mechanical properties of the prepared coatings were studied, and different techniques, such as scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman spectroscopy, and microindentation techniques investigated their microstructure, composition, and phases. The prepared coatings had a multilayer structure with distinct phases of DLC, TiN, and carbide substrate. The potentiodynamic polarization method (PDP) was performed for the DLC/TiN multilayer coatings in 3% NaCl solution to evaluate the corrosion resistance of the prepared coatings. It has been shown that the DLC layer provided the coating with a polarization resistance of 564.46 kΩ. Moreover, it has been demonstrated that the DLC/TiN coatings had a high hardness of 38.7–40.4 GPa, which can help to extend the wood-cutting tools’ life

Enhancement of tribological behavior of rolling bearings by applying a multilayer ZrN/ZrCN coating

This paper focuses on the tribological behaviour of ZrN/ZrCN coating on bearing steel substrates DIN 17230, 100Cr6/1.3505. Coatings are applied at room temperature processes by means of Cathodic Arc Evaporation (CAE), a kind of Physical Vapor Deposition (PVD) technique. In order to achieve a satisfactory compromise between coating-substrate adhesion and the surface roughness requirement of the bearing rings, a polish post-processing is proposed. Different polish post-processing times and conditions are applied. The coated and polished bearing rings are tested under real friction torque test protocols. These tests show that the application of the coating does not entail a significant improvement in friction performance of the bearing. However, fatigue tests in real test bench are pending to evaluate the possible improvement in bearing life time

Friction Mechanisms of 2D Materials--Graphene and MoS2--in Different Environments: Effects of Sliding Induced Defects

This dissertation focuses on studying sliding friction mechanisms of two-dimensional (2D) materials, namely graphene and MoS2, and delineating the effects of structural defects on their coefficient of friction (COF) values under different test atmospheres. Raman, SEM and cross-sectional TEM studies of samples and counterfaces before and after the wear tests in inert and air atmospheres with different relative humidity (RH) levels were used to identify initial microstructures and formation of sliding induced defects at the wear tracks and within the transferred layers. Using density functional theory (DFT) calculations the roles of undissociated and dissociated H2O molecules at defect sites of graphene and MoS2 layers on the interlayer binding energies (EB) were determined. It was shown that the formation of microstructural defects, including vacancies, as well as the changes in the layer structures of the worn surfaces and transfer layers would modify the EB and change the COF, increasing the COF of MoS2 in high humidity but decreasing that of graphene. Sliding friction tests of graphene conducted in ambient air and under a dry N2 atmosphere showed that in both cases a high running-in COF occurred initially but a low steady-state COF (μS) of 0.05 was reached only when the sliding was continued in air with moisture. DFT calculations indicated that the energy barrier (Eb) of 1.27 eV for dissociative adsorption of H2O was significantly lower in case of reconstructed graphene with a monovacancy compared to pristine graphene (3.53 eV). Cross-sectional TEM of graphene transferred to the counterface revealed a partly amorphous structure incorporating damaged graphene layers with d-spacings larger than that of the original layers. DFT calculations on the reconstructed bilayer AB graphene systems revealed an increase of d-spacing due to the chemisorption of H, O, and OH at the vacancy sites and a reduction in the EB by 30% to 0.21 J/m2 between the bilayer graphene interfaces compared to pristine graphene. Thus, sliding induced defects facilitated dissociative adsorption of water molecules and reduced COF of graphene for sliding tests under ambient and humid environments but not under an inert atmosphere. To advance the application that the H, OH passivation of graphene is an essential part for low adhesion for low friction, 5×10-4 wt.% graphene nanoplates (GNP) were vi dispersed in ethanol to lubricate the friction between DLC coated and uncoated tool steel, where a low μS of 0.06 was achieved and the wear rates of the DLC-coated steel were decreased by 70%. Formation of graphene tribolayers on top of steel contact surfaces and sliding induced bending and occasional fragmentation of graphene layers were observed by cross-sectional FIB-TEM. Similarly, addition of carbon nanotubes (CNTs) into ethanol was used to achieve low friction and low adhesion between an Al-alloy engine block material (319 Al) and a common piston ring coating (CrN). The sliding-induced bending and curling of the CNT tribolayers with formation of cylindrical morphology on the Al contact surface were identified by high resolution SEM. Unlike the defect free CVD graphene, magnetron sputtered MoS2 film exhibited a defect structure incorporating misoriented, fragmented layers. The sliding of MoS2 against Ti-6Al-4V showed low friction in vacuum and inert atmosphere but not in humid air. The formation of reoriented MoS2 tribolayers that were parallel to the sliding surfaces produced an increased μS of 0.13 in air with 82% RH instead of an ultra-low value of 0.007 in dry N2. The Raman and HRTEM depicted the formation of MoO3 and the reduced layer spacing of MoS2 in the tribolayers than the value prior to test, which correlated to increased EB. According to the climbing images nudged elastic band (CI-NEB) simulations, H2O dissociated into H/OH at a triple vacancy (a unit MoS2 missing) site of MoS2 (D-MoS2) with an Eb of 0.08 eV, and further to H/O/H again with a low Eb of 0.24 eV. Dissociated H2O and formation of Mo-O-Mo bonds on the MoS2 surface did not change the EB of the MoS2. The undissociated water molecules placed between the bilayer defected MoS2 formed hydrogen bonds with S atoms and increased EB by 20% to 0.37 J/m2, a process that increased the COF. The methodology developed in this study can be used to investigate the friction mechanisms of other 2D layered materials. Rationalization of these friction mechanisms offers guidance for the use of 2D materials in demanding environments in order to reduce friction and mitigate adhesion of engineering surfaces