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.

Multiwalled carbon nanotube (MWCNT) films have been fabricated by using plasma-enhanced chemical vapor deposition system onto Cr–Au patterned alumina substrates, provided with $3\mathrm{nm}$ thick Fe growth catalyst, for $\mathrm{N}{\mathrm{O}}_2$ and $\mathrm{N}{\mathrm{H}}_3$ gas sensing applications, at sensor temperature in the range of $100–250°\mathrm{C}$ . Nanoclusters of noble metal surface catalysts (Au and Pt) have been sputtered on the surface of MWCNTs to enhance the gas sensitivity with respect to unfunctionalized carbon nanotube films. It was found that the gas sensitivity of Pt- and Au-functionalized MWCNT gas sensors significantly improved by a factor up to an order of magnitude through a spillover effect for $\mathrm{N}{\mathrm{H}}_3$ and $\mathrm{N}{\mathrm{O}}_2$ gas detections, respectively. The metal-functionalized MWCNT sensors exhibit very high gas sensitivity, fast response, reversibility, good repeatability, and sub-ppm range detection limit with the sensing properties of the MWCNT films tailored by surface catalyst used to functionalize the MWCNT sensors.

Several applications, where extreme conditions occur, require the use of alloys often containing many critical elements. Due to the ever increasing prices of critical raw materials (CRMs) linked to their high supply risk, and because of their fundamental and large utilization in high tech products and applications, it is extremely important to find viable solutions to save CRMs usage. Apart from increasing processes’ efficiency, substitution, and recycling, one of the alternatives to preserve an alloy and increase its operating lifetime, thus saving the CRMs needed for its manufacturing, is to protect it by a suitable coating or a surface treatment. This review presents the most recent trends in coatings for application in high temperature alloys for aerospace engines. CRMs’ current and future saving scenarios in the alloys and coatings for the aerospace engine are also discussed. The overarching aim of this paper is to raise awareness on the CRMs issue related to the alloys and coating for aerospace, suggesting some mitigation measures without having the ambition nor to give a complete overview of the topic nor a turnkey solution.

TiAlN/AlN multilayers are attracting great interest for the possibility to modulate their mechanical and tribological properties through the variation of multilayer design. In this work TiAlN single layer, TiAlN/AlN intermixed-multilayer and nano-multilayer were prepared using a reactive magnetron sputtering system starting from targets of TiAl and Al. The aim is to analyze how the multilayer design affects the thermal and tribological properties of the coatings. The microstructure of as-deposited and annealed films has been studied using X-ray diffraction. The chemical composition has been deduced by XPS analyses. Thermal behavior was assessed by means of differential thermal analysis (DTA) and thermogravimetric analysis (TGA), while mechanical properties have been investigated by wear tests

Thin films of hafnium oxide have been prepared by using a dual ion beam sputtering system. A study of their physical properties is reported. In particular, structural and compositional characterization was performed by means of x-ray diffraction and x-ray photoelectron spectroscopy techniques, showing a mixture of amorphous and polycrystalline structure and a substoichiometric composition. The atomic force microscopy results have shown a crater-like morphology probably due to the deposition process. In addition the gas sensing characteristics were analyzed in the presence of carbon monoxide. The variations in the electrical resistance have shown the capability of the films to detect CO and then the possibility to use hafnium oxides as a new sensitive material in the field of gas sensors.