Search Results (30)

Traditional binary coatings like TiN and CrN display limited thermal stability and wear resistance under extreme conditions. High-entropy alloy nitride (HEAN) coatings offer a promising solution due to their customizable composition and unique properties, including high hardness, corrosion resistance, and thermal stability. This study focused on (AlCrNbTaTi)N HEAN coatings to address a critical need for materials capable of enduring extreme mechanical and tribological demands by examining the impact of aluminum content on their structural and mechanical properties, providing insights for optimizing coatings in harsh conditions through a self-assembled nanolayer structure with enhanced resilience and performance. The coatings were deposited via a cathodic arc by employing an AlCrNbTaTi alloy target composed of aluminum (20, 50, 60, 70%) and equal molar ratios of Cr, Nb, Ta, and Ti. The coatings were characterized through grazing incidence X-ray diffraction, SEM, HR-TEM, a nano-indentation test, and a friction and wear test. The results indicated that with increasing Al content, the structure of (AlCrNbTaTi)N coatings shifted from FCC to an amorphous state, leading to a reduction in the hardness and elastic modulus, accompanied by an increase in the wear rate and friction coefficient. The (AlCrNbTaTi)N coating, with an equal atomic ratio of metallic elements, showed potential as a hard tool coating. It demonstrated outstanding mechanical and tribological properties, with a 34.5 GPa hardness, 369 GPa modulus, 0.35 friction coefficient, and 8.2 × 10⁻¹⁹ m²·N⁻¹ wear rate. The findings highlight the potential of (AlCrNbTaTi)N coatings to extend tool life and improve operational efficiency, helping advance materials engineering for industrial applications. Full article

Nowadays, the application of protective multicomponent coatings based on hard metal nitrides is increasingly used to increase the resistance of structures and tools to wear, corrosion, and oxidation. In the present work, the multicomponent system Ti-Al-Ta-Si-N is studied, which has high hardness and crack resistance combined with thermal stability and oxidation resistance. The process of formation of the nanocrystalline structure of the coating during its deposition on materials plays a key role in the optimization of these properties. The nanocrystalline structure of the coating is formed due to Si impurity, which is poorly soluble in the Ti_1−x−yAl_xTa_yN system based on B1-TiN and segregates mainly along grain boundaries, forming grain boundary amorphous phases of Si_zN type. In order to find the optimal composition of multicomponent coatings with improved physical and mechanical properties, it is necessary to understand the peculiarities of interaction of Si impurity with the surface of B1-TiN phase in the presence of Al and Ta substitutional impurities. In the present work, with the help of first-principles calculations of electronic and atomic structure of (001) and (111) surfaces of the Ti_1−x−yAl_xTa_yN system with adsorbed Si atom and the interatomic bond study apparatus based on the calculation of a crystal orbital Hamilton population and a crystal orbital bond index, the nature of the bonds between adsorbed Si and the N, Ti, Al, and Ta atoms of the Ti_1−x−yAl_xTa_yN surface system has been studied. It was found that the binding energy of Si with the Ti_1−x−yAl_xTa_yN surface system can be both higher and lower than the binding energy of its bonding with the surface of the binary TiN compound depending on the position of the Al and Ta substitution atoms in the surface layers. The Si bonding with the atoms of the Ti_1−x−yAl_xTa_yN surface is ionic–covalent in nature. It is shown that the Si-Ta interaction has the highest degree of covalency and strength, and the Si-Al interaction is predominantly ionic in most cases considered and is weaker than the Si-Ti and Si-N bonds. Impurity atoms of Al or Ta have very little effect on the Si-Ti and Si-N bonds due to the local nature of the bonds in the Ti_1−x−yAl_xTa_yN surface system with adsorbed silicon atoms. Full article

The Ti-5Al-5V-5Mo-3Cr (Ti-5553) alloy is a relatively novel difficult-to-cut material with limited machinability and tool life analysis available in the literature, and hence requires further investigation. This study focuses on the machining and tribological performance of Ti-5553 under high-speed finish turning (150 m/min, 175 m/min, and 200 m/min) via novel mono/bi-layered PVD-coated WC tools. A base AlTiN coating is used as the reference monolayer coating, with AlCrN, diamond-like ta-C, and TiAlSiN coatings each deposited on top of a base AlTiN coating, totaling four separate coated tools (one monolayer and three bi-layer). Tool life, cutting forces, workpiece surface quality, and tribological chip analysis are among the subjects of investigation in this study. Overall, the AlTiN/AlCrN coated tool outperformed all the other combinations: an improvement of ~19% in terms of tool life in reference to the base AlTiN coating when averaging across the three speeds; lowest surface roughness values: ~0.30, 0.33, and 0.64 µm; as well as the lowest chip back surface roughness values: ~0.80, 0.68, and 0.81 µm at 150, 175, and 200 m/min, respectively. These results indicate that the AlTiN/AlCrN coating is an excellent candidate for industrial applications involving high-speed machining of Ti-5553. Full article

This work uses the direct current magnetron sputtering (DCMS) of equi-atomic (AlTiZrHfTa) and Si targets in dynamic sweep mode to deposit nano-layered (AlTiZrHfTa)N_x/SiN_x refractory high-entropy coatings (RHECs). Transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) are used to investigate the effect of Si addition on the oxidation behavior of the nano-layered coatings. The Si-free nitride coating exhibits FCC structure and columnar morphology, while the Si-doped nitride coatings present a FCC (AlTiZrHfTa)N/amorphous-SiN_x nano-layered architecture. The hardness decreases from 24.3 ± 1.0 GPa to 17.5 ± 1.0 GPa because of the nano-layered architecture, whilst Young’s modulus reduces from 188.0 ± 1.0 GPa to roughly 162.4 ± 1.0 GPa. By increasing the thickness of the SiN_x nano-layer, k_p values decrease significantly from 3.36 × 10⁻⁸ g² cm⁻⁴ h⁻¹ to 6.06 × 10⁻⁹ g² cm⁻⁴ h⁻¹. The activation energy increases from 90.8 kJ·mol⁻¹ for (AlTiZrHfTa)N_x nitride coating to 126.52 kJ·mol⁻¹ for the (AlTiZrHfTa)N_x/SiN_x nano-layered coating. The formation of a FCC (AlTiZrHfTa)-N_x/a-SiN_x nano-layered architecture results in the improvement of the resistance to oxidation at high temperature. Full article

Due to its inherent high hardness, strength, and plasticity, tantalum–tungsten (Ta-W) alloy poses a considerable challenge in machining, resulting in pronounced tool wear, diminished tool lifespan, and suboptimal surface quality. This study undertook experiments utilizing uncoated carbide tools, TiAlN-coated carbide tools, and AlTiN-coated carbide tools for machining Ta-2.5W alloy. The investigation delved into the intricacies of surface temperature, tool longevity, and the distinctive wear characteristics under varying coating materials and cutting parameters. Concurrently, a comprehensive exploration of the wear mechanisms affecting the tools was conducted. Among the observed wear modes, flank wear emerged as the predominant issue for turning tools. Across all three tool types, adhesive wear and diffusion wear were identified as the principal wear mechanisms, with the TiAlN-coated tools displaying a reduced level of wear compared to their AlTiN-coated counterparts. The experimental findings conclusively revealed that TiAlN-coated carbide tools exhibited an extended tool lifespan in comparison to uncoated carbide tools and AlTiN-coated carbide tools, signifying superior cutting performance. Full article

Tantalum–tungsten alloys have been widely used in different industrial sectors—for example, in chemical, medical, aerospace, and military equipment. However, they are usually difficult to cut because of the large cutting force, rapid tool wear, and poor surface finish during machining. This paper presents the machining performance and cutting tool wear of AlCrN/TiAlN-coated carbide tools during the milling process of Ta-2.5W. The effects of cutting parameters on the cutting forces and surface roughness of AlCrN/TiAlN-coated carbide tools were obtained and analyzed. The results show that the wear resistance of AlCrN-coated tools is better than that of TiAlN-coated tools, and that the main wear mechanisms of both cutting tools are crater wear, adhesive wear, and diffusion wear. Compared to TiAlN-coated tools, AlCrN-coated tools reduced the cutting forces by 1% to 15% and decreased the surface roughness by 6% to 20%. A cutting speed within the range of 80–120 m/min can ensure a low cutting force while maintaining good surface roughness, which is more conducive to machining Ta-2.5W. Full article

The structural, mechanical, and electronic properties of cubic Cr_0.5-xAl_0.5TM_xN, doped with TM (transition metal) elements (TM = Ti, V, Y, Zr, Hf, and Ta) at low concentrations (x = 0.03 and 0.06), was investigated by first-principles calculations. The results of the structural properties calculations reveal that the addition of Ti, Y, Hf, Zr, and Ta expand the volume, while V has the opposite effect. All doped compounds are thermodynamically stable, and Cr_0.5-xAl_0.5TM_xN with TM = Ti is energetically more favorable than other doped compounds. At the same doping concentration, Cr_0.5-xAl_0.5V_xN possesses the highest stiffness, hardness, and resistance to external forces due to its greatest mechanical properties, and Cr_0.5-xAl_0.5Ta_xN possesses the highest elastic anisotropy and the lowest Young’s modulus. Substituting Cr atoms with TM atoms in a stepwise manner results in a decrease in the bulk modulus, shear modulus, Young’s modulus, and theoretical hardness of Cr_0.5-xAl_0.5TMxN, while increasing its toughness. Based on the calculation results of the total and partial density of states of Cr_0.5Al_0.5N and Cr_0.47Al_0.5TM_0.03N, all compounds exhibit metallic behavior as indicated by the finite density of states at the Fermi level. The contribution of Ti-3d, V-3d, and Ta-3d orbitals at Fermi level is significantly higher than that of other TM atoms, resulting in a more pronounced metallic character for Cr_0.47Al_0.5Ti_0.03N, Cr_0.47Al_0.5V_0.03N, and Cr_0.47Al_0.5Ta_0.03N. Full article

A consistent evolution in materials developed for the industry and chip-start cutting processes has been acknowledged over the years. Cutting tool improvement through applying advanced coatings has proven very effective, enabling tool life (TL) extension while ensuring better surface quality. TiAlTaN coating enhances TL and surface quality in machining processes. However, only minimal research has been dedicated to comprehending the interaction between workpieces composed of Cu-Be and diamond tools. AMPCO^®, a Cu-Be alloy, plays a crucial role in moulding inserts, offering high wear resistance and contributing to extended mould longevity and improved productivity. The main objective of this work is to assess, identify, and quantify tool wear (TW) mechanisms evaluation while machining AMPCO^® with WC-Co uncoated tools and TiAlTaN-coated tools by physical vapour deposition (PVD). Evaluating tool performance while varying cutting length (L_cut) and feed rate (f) at three distinct levels and analysing the surface roughness (SR) produced in the machined surface were the primary purposes of this work. The results obtained with coated tools were distinct from those obtained with uncoated tools. While uncoated tools suffered from substrate abrasion and adhesion, the coated tools suffered mainly from delamination, followed by chipping. Furthermore, f and L_cut significantly influence the quality of the machined surface. TiAlTaN-coated tools performed significantly worse than uncoated tools, proving that the coating needs significant improvements to be considered as an alternative in milling Cu-Be alloys. Full article

The high-entropy PVD coating (AlCrZrTiTa)N, characterized by its high hardness (50–60 GPa), elastic modulus above 300 MPa, and high heat resistance up to 1300 °C, is used for coating cutting tools operating under extreme metalworking conditions. The nanostructured monolayer 3 μm PVD coating was deposited on cutting plates in the hybrid arc deposition PVD coater. The coating had an amorphous nanocrystalline microstructure with a grain size of about 10–50 nm. The samples of SS 304 steel were investigated during dry high-speed (600 m/min) cutting. Raman spectroscopy was used to study the formation of tribooxides on the tool surface at the running-in stage of the cutting. After 130 m of cutting, Cr₂O₃ oxide appears on the wear surface while other elements are bound with N atoms. When the cutting length is increased to up to 260 m, oxide Al₂O₃ · ZrO₂ (mullite) and amorphous oxides TaO₂ and CrO₂ are formed. The method EELFS made it possible to determine the amorphous nanocrystalline structure of triboceramics based on CrO₂ and Al₂O₃ · ZrO₂. The nearest atomic surrounding of Cr-Cr, O-O, and Cr-O and their subsequent comparison with the available literature data allow us to calculate the equilibrium lattice constants of the CrO₂ unit cell, which are equal to (a, b) = 4.3754 Å and c = 0.5927. The triboceramic films on the base of non-equilibrium mullite Al₂O₃·ZrO₂ have an amorphous structure. In the first coordination sphere, the interatomic distances of Zr-O and Al-O were 1.79 and 1.89 Å. An accelerated adaptive reaction to extreme external stimuli, at the very beginning of the running-in stage, is established. The tribological adaptability of the high-entropy ultra-fine amorphous nanocrystalline coating under extremely loaded dry high-speed cutting is based on non-equilibrium phenomena: the partial oxidation of fragments of the nitride and dynamic formation of protective tribooxides, which have a good thermal barrier and frictional properties. These factors interact synergistically and determine the life of the cutting tool. Full article

Nowadays, the application of multicomponent coatings with multiphase nanocrystalline structure is the most promising direction in the search for wear-resistant protective coatings with a full set of necessary operational properties. Nanocrystalline multicomponent coatings based on the Ti-Al-Ta-Si-N system have a high hardness combined with thermal stability and oxidation resistance. Silicon atoms are weakly soluble in the TiN, Ti_1−xAl_xN, and TaN crystalline phases of the Ti-Al-Ta-Si-N system and interact preferentially with N atoms, forming the amorphous Si₃N₄ phase. In this context, it is important to first study the peculiarities of the interaction of Si atoms with the simplest structural units of the Ti-Al-Ta-Si-N system, such as TiN, AlN, and TaN compounds with the NaCl structure. This work is devoted to the study of the interaction of a Si atom with the (001) surface of AlN, TiN, and TaN compounds with the NaCl structure using ab initio calculations. This provides information for a deep understanding of the initial stages of the formation of different crystallites of the considered composite. It was established that the adsorption of silicon on the (001) surface of AlN, TiN, and TaN significantly increases the relaxation of the surface layers and leads to an increase in the corrugation observed on the clean surfaces. The largest corrugation is observed on the surface of the TaN compound. The most energetically favorable adsorption positions of Si atoms were found to be the position of Si above the N atom on the TiN and TaN surfaces and the quadruple coordinated position on the AlN surface. The valence electron density distribution and the crystal orbital Hamiltonian population were studied to identify the type of Si atom bonding with the (001) surface of AlN, TiN, and TaN compounds. It was found that silicon forms predominantly covalent bonds with the nearest metal and nitrogen atoms, except for the quadruple coordinated position on the surface of TiN and TaN, where there is a high degree of ionic bonding of silicon with surface atoms. Full article

Ti-Al-Ta-N coatings are characterized by attractive mechanical properties, thermal stability and oxidation resistance, which are superior to ternary compositions, such as Ti-Al-N. However, because of their open columnar microstructure, the Ti-Al-Ta-N coatings deposited by conventional direct current magnetron sputtering (DCMS) exhibit insufficient wear resistance. This work is focused on obtaining the Ti-Al-Ta-N coatings with improved microstructure and mechanical and tribological properties by middle-frequency magnetron sputtering (MFMS). The coatings are deposited by the co-sputtering of two separate targets (Ti-Al and Ta) using pure DCMS and MFMS modes as well as hybrid modes. It is found that the MFMS coating has a denser microstructure consisting of fragmented columnar grains interspersed with equiaxed grains and a smaller grain size than the DCMS coating, which is characterized by a fully columnar microstructure. The modification of the microstructure of the MFMS coating results in the simultaneous enhancement of its hardness, toughness and adhesion. As a result, the wear rate of the MFMS coating is less than half of that of the DCMS coating. Full article

The main objective of this work was to assess and compare the structure and mechanical properties of the TiN and TiAlN coatings deposited on a new WC-Co tool using the cathodic arc evaporation vacuum deposition (CAE-PVD) technique. The cutting tool was sintered at high temperature and high pressure using a powder tungsten carbide matrix ligated with cobalt (WC-Co). Powdered grain growth inhibitors (TiC, TaC, and NbC) were admixed into the matrix to enhance its strength and to facilitate the adhesion of the Ti base coatings. Detailed scanning electron microscopy with energy-dispersive spectrometry (SEM-EDS) and X-ray diffraction (XRD) analyses were performed, aiming to substantiate the effectiveness of the inhibitor additions. XRD data were thoroughly exploited to estimate the phase contents, average crystallite sizes (D), coating thicknesses (t), texture coefficients (T_hkl), and residual stress levels (σ). Atomic force microscopy (AFM) was used to calculate the average roughness (Ra) and the root mean square (Rq). The microhardness (µHV) was measured using the Vickers method. The TiAlN characteristics (D = 55 nm, t = 3.6 μm, T₂₀₀ = 1.55, µHV = 3187; σ = −2.8 GPa, R_a = 209 nm, R_q = 268 nm) compared to TiN ones (D = 66 nm, t = 4.3 μm, T₁₁₁ = 1.52, µHV = 2174; σ = +2.2 GPa, R_a = 246 nm, R_q = 309 nm) substantiate the better adequacy of the TiAlN coating for the WC-Co substrate. The structural features and data on the TiN and TiAlN coatings, the tool type, the different stress kinds exerted into these coatings, and the way of discrimination of the coating adequacy are the novelties addressed in the paper. Full article

A multilayer structure and incorporation of the fourth element are promising strategies to improve the properties of TiAlN coatings. In this study, the structural, mechanical, and thermal properties of the Ti_0.34Al_0.48Ta_0.18N/Ti_0.42Al_0.54B_0.04N multilayer, as well as the Ti_0.34Al_0.48Ta_0.18N and Ti_0.42Al_0.54B_0.04N monolithic coatings, were carefully researched. Coherent growth of the multilayer structure induces a single-phase cubic structure of the Ti_0.34Al_0.48Ta_0.18N/Ti_0.42Al_0.54B_0.04N multilayer, even though the Ti_0.34Al_0.48Ta_0.18N and Ti_0.42Al_0.54B_0.04N coatings have a single-phase cubic structure and a mixed cubic and wurtzite structure, respectively. The Ti_0.34Al_0.48Ta_0.18N/Ti_0.42Al_0.54B_0.04N multilayer reveals a higher hardness of 38.2 ± 0.9 GPa due to interfacial strengthening, corresponding to 32.4 ± 0.6 GPa of Ti_0.34Al_0.48Ta_0.18N and 32.7 ± 0.9 GPa of Ti_0.42Al_0.54B_0.04N. During annealing, our three kinds of coating demonstrate an age-hardening effect. The Ti_0.34Al_0.48Ta_0.18N/Ti_0.42Al_0.54B_0.04N multilayer presents a hardness peak of 40.0 ± 0.9 GPa at 1000 °C, whereas the Ti_0.34Al_0.48Ta_0.18N and Ti_0.34Al_0.48Ta_0.18N coatings show the hardness peaks of 37.1 ± 0.7 and 35.0 ± 0.6 GPa at 900 °C, respectively. Furthermore, the improved oxidation resistance is obtained by the Ti_0.34Al_0.48Ta_0.18N/Ti_0.42Al_0.54B_0.04N multilayer. Full article

The present paper reports a new way to improve the wear resistance of coated carbide tools by increases in TiC content and the addition of TaC in substrates. The results suggest that the average grain size of the substrate increased with the increases in TiC (0–14 wt.%) content, and the hardness of the TiAlN coating deposited on the substrate exhibits a similar trend. In addition, the adhesion strength of the TiAlN-coated carbide increases with increasing TiC content, which can be attributed the formation of the (Ti,W)C phase and the similar hardness of the substrate and coating. The addition of TaC into the substrates inhibits the grain growth and thereby causes the hardness and adhesion strength of the TiAlN coatings to improve from 24.6 GPa and 16.7 N to 30.1 GPa and 17.3 N, respectively. In turning tests, the TiAlN coating deposited on the substrates with the TaC addition achieved the best wear resistance in turning stainless steel because it possessed the highest substrate and coating hardness and sufficient adhesion strength. However, the TiAlN coating deposited on the substrates with a higher TiC content shows the better wear resistance in turning titanium (TC4), which can be attributed to it having the highest adhesion strength. Full article

Si₃N₄/TaC composite MAO coatings were fabricated by microarc oxidation (MAO) on a Ti–6Al–4V (TC4) alloy in a phosphate-based electrolyte containing Si₃N₄/TaC mixed particles. The influence of the amount of Si₃N₄/TaC particles on the microstructure, composition, tribological behavior, and corrosion properties of the MAO coatings has been investigated. Morphological research of the MAO coatings was carried out using scanning electron microscopy (SEM), with the surface porosity analyzed by ImageJ software. X-ray diffraction (XRD) was used for the detection of the phase characteristic of the MAO coatings, and an abrasive wear test and electrochemical measurements were conducted in the artificial seawater solution by the ball-on-disc friction tester and the electrochemical workstation, respectively. The results showed that Si₃N₄/TaC particles could be successfully incorporated into the composite coatings, and the addition of Si₃N₄/TaC particles greatly reduced the porosity of the coatings, thus improving both tribological and corrosion properties of the composite MAO coatings. The composite MAO coating with the addition of 1 g/L Si₃N₄ + 0.5 g/L TaC particles showed the best tribological property and the optimum corrosion properties. Full article