The machining process is still a very relevant process in today’s industry, being used to produce high quality parts for multiple industry sectors. The machining processes are heavily researched, with the focus on the improvement of these processes. One of these process improvements was the creation and implementation of tool coatings in various machining operations. These coatings improved overall process productivity and tool-life, with new coatings being developed for various machining applications. TiAlN coatings are still very present in today’s industry, being used due to its incredible wear behavior at high machining speeds, high mechanical properties, having a high-thermal stability and high corrosion resistance even at high machining temperatures. Novel TiAlN-based coatings doped with Ru, Mo and Ta are currently under investigation, as they show tremendous potential in terms of mechanical properties and wear behavior improvement. With the improvement of deposition technology, recent research seems to focus primarily on the study of nanolayered and nanocomposite TiAlN-based coatings, as the thinner layers improve drastically these coating’s beneficial properties for machining applications. In this review, the recent developments of TiAlN-based coatings are going to be presented, analyzed and their mechanical properties and cutting behavior for the turning and milling processes are compared.

It is well known that injection of glass fibre–reinforced plastics (GFRP) causes abrasive wear in moulds’ cavities and runners. Physical vapour deposition (PVD) coatings are intensively used to improve the wear resistance of different tools, also being one of the most promising ways to increase the moulds’ lifespan, mainly when used with plastics strongly reinforced with glass fibres. This work compares four different thin, hard coatings obtained using the PVD magnetron sputtering process: TiAlN, TiAlSiN, CrN/TiAlCrSiN and CrN/CrCN/DLC. The first two are monolayer coatings while the last ones are nanostructured and consist of multilayer systems. In order to carry out the corresponding tribological characterization, two different approaches were selected: A laboratorial method, using micro-abrasion wear tests based on a ball-cratering configuration, and an industrial mode, analysing the wear resistance of the coated samples when inserted in a plastic injection mould. As expected, the wear phenomena are not equivalent and the results between micro-abrasion and industrial tests are not similar due to the different means used to promote the abrasion. The best wear resistance performance in the laboratorial wear tests was attained by the TiAlN monolayer coating while the best performance in the industrial wear tests was obtained by the CrN/TiAlCrSiN nanostructured multilayer coating.

Duplex stainless steels are being used on applications that require high corrosion resistance and excellent mechanical properties, such as the naval and oil-gas exploration industry. The components employed in these industries are usually obtained by machining; however, these alloys have low machinability when compared to conventional stainless steels, usually requiring the employment of tool coatings. In the present work, a comparative study of TiAlSiN coating performance obtained by these two techniques in the milling of duplex stainless-steel alloy LDX 2101 was carried out. These coatings were obtained by the conventional direct current magnetron sputtering (dc MS) and the novel high power impulse magnetron sputtering (HiPIMS). The coatings were analyzed and characterized, determining mechanical properties for both coatings, registering slightly higher mechanical properties for the HiPIMS-obtained coating. Machining tests were performed with varying cutting length and feed-rate, while maintaining constant values for axial and radial depth of cut and cutting speed. The surface roughness of the material after machining was assessed, as well as the wear sustained by each of the tool types, identifying the wear mechanisms and behavior of these tools, as well as registering the flank wear values presented for each of the tested tools. The HiPIMS-obtained coating exhibited a very similar behavior when compared to the other, producing similar surface roughness quality. However, the HiPIMS coating exhibited less wear for higher cutting lengths, proving to be a better choice in this case, especially regarding tool life.

Micro-abrasion remains a test configuration hugely used, mainly for thin coatings. Several studies have been carried out investigating the parameters around this configuration. Recently, a new study was launched studying the behavior of different ball materials in abrasive particles’ dynamics in the contact area. This study intends to extend that study, investigating new ball materials never used so far in this test configuration. Thus, commercial balls of American Iron and Steel Institute (AISI) 52100 steel, Stainless Steel (SS) (AISI) 304 steel and Polytetrafluoroethylene (PTFE) were used under different test conditions and abrasive particles, using always the same coating for reference. Craters generated on the coated samples’ surface and tracks on the balls’ surface were carefully observed by Scanning Electron Microscopy (SEM) and 3D microscopy in order to understand the abrasive particles’ dynamics. As a softer material, more abrasive particles were entrapped on the PTFE ball’s surface, generating grooving wear on the samples. SS AISI 304 balls, being softer than the abrasive particles (diamond), also allowed particle entrapment, originating from grooving wear. AISI 52100 steel balls presented particle dynamics that are already known. Thus, this study extends the knowledge already existing, allowing to better select the ball material to be used in ball-cratering tests.

The food industry is increasingly demanding in terms of the quality and appearance of its product packages. The present study focuses on identifying the main wear mechanisms developed during the stamping process of these packages. During the stamping process, the presence of a tin layer on the surface of the sheet used creates difficulties in the stamping due to the transfer of material from the sheet to the tool, addition of the coefficient of friction, and premature wear of some surfaces of the tool where the contact is more pronounced. In order to understand and avoid these phenomena, a TiAlN coating deposited by a physical vapor deposition (PVD) process was used, which was studied in the laboratory to analyze the evolution of the friction force on the contact and to verify the reaction of the coating on contact with tinplate. Afterwards, the tool was coated and practical tests were performed on the stamping. The obtained results allow confirmation of a significant improvement of the wear behavior of the tool when provided with the coating and also verify that this coating presented better wear resistance than others previously tested in the same working conditions.

There are several ways to characterize the wear resistance of coatings in the laboratory, almost all of them applying relatively low contact pressure, both punctually and over surface contact. Pin-on-disc, reciprocal sliding, and micro-abrasion wear tests are quite common configurations for this purpose. Thus, a gap was identified in terms of characterization of hard physical vapor deposition (PVD) coatings subject to higher levels of contact pressure. This study aims to study and compare the wear behavior of two different coatings made by PVD, a B₄C (Boron Carbide) monolayer, less used, and another following a multilayer structure of CrN/CrCN/DLC, to identify the wear mechanisms involved in quite different coatings. Both coatings were initially characterized in terms of chemical composition, thickness, morphology, structure, hardness, and adhesion to the substrate, being subsequently tested in laboratory equipment for wear tests following the block-on-ring configuration and relatively high levels of contact pressure, with a view to study the failure mechanisms of the coatings and their wearrate. CrN/CrCN/DLC multilayered coatings presented a better overall wear behavior, whereas B₄C coating showed a good wear behavior regarding the load and configuration used, but in line with the behavior already observed when other wear testing configurations had been used. Thus, under the conditions imposed, CrN/CrCN/DLC coating is the best option when high contact pressure is applied to the coated surfaces.