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.

The main regularities of the formation of microstructure and properties of multilayer nanostructured CrN/MoN films with periodically changing architecture of layers were considered. The transition metal nitride coatings with high hardness and wear resistance were obtained by vacuum-arc evaporation of the cathodes (Arc-PVD) in nitrogen atmosphere at several sets of predetermined deposition parameters. CrN/MoN multilayers were fabricated using constant nitrogen pressure of 0.4, 0.09 and 0.03 Pa. All samples were divided into three main series depending on the values of bias voltage applied to the substrates (-20,-150 and-300 V). Each serial of samples contain multilayer films varying in the individual layer deposition time and, hence, thickness, which is in range from 1.7 µm to 20 nm. The morphology of surface and microstructure of cross-sections were studied by scanning electron microscopy (SEM). Elemental composition and elemental depth profiles were characterised by energy-dispersive X-ray spectroscopy (EDS), secondary-ion mass spectrometry (SIMS), Rutherford backscattering spectrometry (RBS) and high-resolution transmission electron microscopy (HRTEM) EDS. Micro-and nanostructural analysis of the films was performed by X-ray diffractometry (XRD), grazing incidence XRD (GIXRD), in-plane XRD, electron backscatter diffraction (EBSD) and HRTEM selected area electron diffraction (SAED). The main phases formed in films were two CrN and γ-Mo 2 N nitride phases with cubic lattice of NaCl type and not significant volume of additional metastable MoN cubic phase depending on nitrogen pressure and bias voltage. The preferential orientation of planes changes from [311] to [111] and [200] with the increase of absolute value of bias voltage from-20 V to-150 V and-300 V respectively. The size of nanograins in coatings with a nanometre bilayers thickness was about 12 nm, while micro-deformation of nanocrystallites was about 0.5-0.6%. Coatings with thin nanoscale bilayers have shown high hardness (38-42 GPa) and strong wear resistance, which makes them appropriate and promising for industrial applications as protective ones. The relations between deposition conditions and obtained composition, structure and features were studied. The best parameters and deposition conditions were discussed as recommended to achieve superior mechanical and physical properties of coatings with long lifetime and applicable for harsh environment.

We report on CrN/MoN multilayer coatings, their structure, elemental and phase composition, residual stresses, mechanical properties and their dependence on deposition conditions. The hardness and toughness were considered as main parameters for improvement of the protective properties of coatings. Multilayers with varying bilayer periods, ranging from 40 nm to 2.2 mm, were obtained by using cathodic arc physical vapour deposition (Arc-PVD) on stainless steel substrate. The elemental analysis was performed using wavelength-dispersive X-ray spectroscopy (WDS). The surface morphology and cross-sections were analysed with scanning electron microscopy (SEM). The X-ray diffraction (XRD) measurements, including grazing incidence X-ray diffraction (GIXRD), in-plane diffraction analysis and electron backscatter diffraction (EBSD), were used for microstructure characterisation. Mechanical properties of deposited films were studied by measuring hardness (H) and Young's modulus (E) with micro-indentation, H/E and H 3 /E 2 ratios were calculated. The dependences of internal structure and, hence, mechanical properties, on layer thickness of films have been found.