Structural characterization and adhesion appraisal of TiN and TiCN coatings deposited by CAE-PVD technique on a new carbide composite cutting tool

A new composite matrix was developed for a cutting tool based on tungsten carbide ligated with cobalt (WC-Co) using sintering technique. The admixtures of niobium carbide, tantalum carbide, and titanium carbide with the WC-Co matrix aim to inhibit the grain growth of WC and to promote covalent bonding at the interface. The modified WC-Co tools were coated with titanium nitride and titanium carbonitride layers by CAE-PVD technique. To substantiate the performances of the new coating-substrate systems, we have performed X-ray diffraction, atomic force microscopy, and scratch test measurements to estimate: phase content, average crystallite size, average texture coefficient, residual stress level, coating thickness, average roughness, square mean root, fractal dimension, cohesive adhesion, and adhesive adhesion. The results enable the in-depth understanding of the coating growth mechanisms and provide an objective evaluation of the coatings adhesion to the new cutting tools matrix. The results provide evidence to support the potential of TiN and TiCN coatings to enhance the working performances of the composite WC-Co cutting tools and to differentiate their properties. TiCN coating is shown to be superior to TiN coating in terms of adhesion and thus represents a better alternative for coating the modified WC-Co composite matrix.     

Applicability of DLC and WC/C low friction coatings on Al2O3/TiCN mixed ceramic cutting tools for dry machining of hardened 52100 steel

The present work examines the applicability of DLC and WC/C low friction coatings on Al₂O₃/TiCN based mixed ceramic cutting tools for the dry and hard turning of AISI 52100 steel (62 HRC). The characterization of coated tools reveals that the coatings retain very low values of surface roughness, whereas the DLC coating exhibits much higher microhardness when compared to the WC/C coating. On the other hand, the WC/C coating exhibit a coarse surface morphology virtually due to the tungsten doping. Later, continuous turning tests were executed with the help of coated and uncoated cutting tools under dry cutting conditions, and their performance was investigated in terms of machining forces, cutting temperature and tool wear. Coating delamination by flaking and peeling is quite prominent in the case of both the coatings; however, it is less severe for the WC/C coated tool. The coatings help to reduce machining forces, cutting temperatures and tool wear, but the performance of coated tools converge towards uncoated tool as the cutting speed, and feed rate is increased. Both the coatings prevent the development of cracks near the cutting edge with WC/C coating exhibiting superior wear behavior basically due to its multilayered structure and better thermal stability. Moreover, the tested low friction coatings don't serve as thermal barriers and only the lubrication generated due to graphitization at the chip-tool interface is mostly responsible for the improved machining performance.     

高能量密度脉冲等离子枪在硬质合金刀具上沉积高硬耐磨涂层研究

用高能量密度脉冲等离子体枪，于室温下在硬质合金刀具基体上分别成功沉积了硬度高、耐磨损、膜基结合力强的TiN、TiCN和TiAlN薄膜。在优化的工艺条件下，所得TiN、TiCN、TiAlN薄膜纳米硬度分别可达27GPa、50GPa和38GPa；杨氏模量分别可达450GPa、550GPa、650GPa。纳米划痕实验临界载荷分别达90mN、110mN和100mN以上。切削实验表明，涂层刀具可用于高速切削，刀具后面磨损明显减小。刀具力学性能的改善归因于更优异力学性能涂层的沉积、良好的膜基结合力以及涂层特殊的显微结构。     

Wear behaviors of TiN/TiCN/DLC composite coatings in different environments

Diamond like carbon (DLC) coatings have high wear resistance and low coefficient of friction and its features are being tried to be further developed. We deposited TiN/TiCN/DLC composite coatings on inconel substrates with closed field unbalanced magnetron sputtering system to improve the features of the conventional DLC coatings. Structural, chemical and bond types of the coating were obtained with the XRD, SEM, EDS and XPS analyses. Wear behaviors of the coatings were determined in atmosphere, distillated water and commercial oil conditions under low (2 N) and high (10 N) constant load values with using pin-on-disc tribo-test system. The wear results demonstrated that using the TiN/TiCN layers with the DLC coatings increased the load carrying capacity, decreased the CoF, and wear rates at the high load values.     

Hard machining performance of PVD AlCrN coated Al2O3/TiCN ceramic inserts as a function of thin film thickness

In the present work, AlCrN coating was deposited on Al₂O₃/TiCN ceramic inserts with varying thin film thickness using physical vapor deposition (PVD) technique. The thickness, surface morphology, chemical composition, hardness and adhesion strength of the coating to the substrate were characterized by field-emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), micro-indentations and scratch tests respectively. The machining performance of uncoated and coated tools was investigated in hard turning of AISI 52100 steel (62 HRC) under dry environment. The cutting behavior was analyzed in terms of machining forces, tool temperature, wear, friction and chip morphology. Further, a 3D finite element model with hybrid friction criterion has been adopted to support the experimental findings. The results revealed that coating/substrate adhesion and edge radius were the deciding criteria for the machining performance of coated tools with 3 µm coating thickness tool exhibiting best turning performance on Al₂O₃/TiCN mixed ceramic insert.     

Properties of TiN–Al2O3–TiCN–TiN,TiAlN, and DLC-coated Ti(C,N)-based cermets and their wear behaviors during dry cutting of 7075 aluminum alloys

In the work, TiAlN for physical vapor deposition (PVD), multilayer TiN-Al₂O₃-TiCN-TiN for chemical vapor deposition (CVD), and diamond-like carbon (DLC) for plasma-enhanced chemical vapor deposition (PECVD) were deposited on the cermet inserts. Characteristics and wear behaviors of the three coated cermets during dry cutting of 7075 aluminum alloys were observed. The results show that TiN-Al₂O₃-TiCN-TiN coatings have highest adhesion strength and hardness. At the cutting speed of 1100 r/min, the depth of 0.2 mm, and the feed rate of 0.1 mm/r, the three coated inserts show the best wear-resistant properties. In this case, TiN/Al₂O₃/TiCN/TiN shows the worst wear-resistant properties (value of the flank wear [VBB] = 0.062 mm), while DLC coatings show the most excellent wear-resistant properties (VBB = 0.046 mm). During the cutting of aluminum alloys, which have high plasticity and low melting point, adhesive wear dominate on the flank of the inserts. The thickest coating of TiN/Al₂O₃/TiCN/TiN results in the bluntest cutting edge, which form the most serious adhesive worn zone. For the TiAlN and DLC coatings, due to a smaller cutting force, the two coatings have much better wear resistance. Further, the self-lubricating properties of DLC show excellent effect on protecting the inserts. Thus, the DLC-coated cermets have the best wear-resistant properties. Further, the TiAlN-coated cermets have the widest wear-affected zone while the DLC coating has the narrowest.     

The crystallization behaviours of reactive-plasma-sprayed TiCN coatings with different Ti/graphite powder ratios

TiCN coatings were reactive plasma sprayed with different Ti/graphite powder ratios. Their crystallization behaviours were investigated. The results showed that the TiN coating consisted of TiN and TiN_0.3O phases. With the decrease in the Ti/graphite ratios, the phases in the coatings changed from TiC_0.7N_0.3+TiC_0.3N_0.7+amorphous (Ti:graphite = (6-10):1) to TiC_0.3N_0.7 + TiC + amorphous (Ti:graphite = 4:1). The surface of the TiN coating exhibited the columnar crystals. With the decrease in the Ti/graphite ratios, the columnar crystals gradually skewed towards the surface. The cross-section crystalline morphologies of all the coatings exhibited the layer-layer columnar crystals with better bonding interfaces between the layers. The micro-hardness of the sprayed TiN coating was 1000 HV_0.1. The micro-hardness of the TiCN coatings increased with the decrease in the Ti/graphite ratios. The maximum microhardness (1315 HV_0.1) was observed at a Ti/graphite ratio of 4:1, approximately 30% higher than that of the TiN coating. The increase in the micro-hardness was correlated with the phase composition and crystalline morphologies.     

TiCN涂层的制备及其微观结构和性能

采用直流磁控溅射法在AZ31镁合金上制备了TiCN涂层.采用X射线荧光光谱仪、扫描电镜和X射线衍射仪表征了涂层的化学成分、表面形貌和物相,并采用电化学阻抗谱、浸泡试验、显微硬度测试和磨损试验考察了基体偏压(-40、-60和-80 V)对涂层性能的影响.结果表明,涂层由TiCN和TiN组成.随着负偏压增大,涂层中Ti、C...     

Electron beam assisted physical vapor deposition of very hard TiCN coating with nanoscale characters

The work concerns electron beam assisted physical vapor deposition (EB-PVD) of titanium carbo-nitride (TiCN) on D2 tool steel. First, D2 steel substrate was heat treated to support and improve the load bearing capacity of the coating. To reduce the intrinsic gap between D2 substrate and TiCN coating and to improve the adhesive strength of the coating, a thin bond coat of Ti was EB-PV deposited on D2 steel prior to TiCN coating. The deposited coating was characterized in depth using XRD, SEM, AFM, profilometry and nanoindentation; its performance was assessed by the wear tests. The results demonstrated that EB-PVD process is successful in uniform deposition of nanograined (5.7 nm) TiCN coating; this character of the coating enhances its mechanical responses and cohesive strength. AFM topographic characterization confirms nanoscale smoothness of the TiCN coating which is a key factor in upgrading the wear resistance and tribological behavior of the coating. Nanoindentation results showed that the deposited coating is very hard; it is also tough enough. The hardness of the TiCN in this work is too much higher than those reported in the literature by similar works. AFM and nanoindentation results showed that a TiCN coating with thickness of 1.6 μm and roughness of 22 nm exhibits a hardness of 3552 HV which is much higher than those hardnesses reported in previous works. The wear tests showed that the deposited TiCN coating has a higher wear resistance than the D2 steel as well as TiN coating; this better performance is attributed to the modifications made in the coating process and its nanoscale characters.     

Tribomechanical and microstructural properties of cathodic arc-deposited ternary nitride coatings

Sintered carbides are promising materials for surfaces that are exposed to extreme wear. Owing to their high service load, ceramic-based thin films are coated on carbides using different techniques. In this study, non-toxic and cobalt-free powder metallurgy-sintered carbide samples were coated with TiN, TiAlN, CrAlN, and TiSiN ceramic-based thin film coatings by cathodic arc physical vapor deposition. The microstructure (phase formation, coating thickness, surface roughness, and topography), mechanical properties (hardness, modulus of elasticity, and plasticity indices), and tribological properties (nanoscratch and wear behavior) of the thin film coatings were investigated. No cracks or defects were detected in these layers. The ceramic-based ternary nitride thin film coatings exhibited better mechanical performance than the TiN coating. The TiN thin film coating had the highest average surface roughness, which deteriorated its tribological performance. The ternary nitride thin film coatings exhibited high toughness, while the TiN thin film coating exhibited brittle behavior under applied loads when subjected to nanoscratch tests. The wear resistance of the ternary nitride coatings increased by nearly 9–17 times as compared to that of the TiN coating and substrate. Among all the samples investigated, the substrate showed the highest coefficient of friction (COF), while the TiSiN coating exhibited the lowest COF. The TiSiN thin film coating showed improved mechanical and tribological properties as compared to other binary and ternary nitride thin film coatings.     

Diamond coatings for micro end mills: Enabling the dry machining of aluminum at the micro-scale

We show that thin diamond coatings can dramatically enhance the performance of micrometer-scale cutting tools. We present a new approach for coating 300 μm diameter tungsten carbide (WC) micro end mills using a tailored seeding method and hot filament chemical vapor deposition (HFCVD) to obtain uniform, conformal, and continuous diamond coatings less than 2 μm in both thickness and grain size. The performance of the uncoated and coated tools has been evaluated by dry machining channels in 6061-T6 aluminum. The test results demonstrate far lower tool wear and breakage, much lower adhesion of aluminum to the tool, and significantly lower cutting forces for the coated tools. The coatings achieve a more predictable surface finish and enable dry machining at high speeds (40,000 rpm) with little or no burr formation. The improved performance of the coated tools is a result of the superior tribological properties of fine-grained diamond against aluminum, specifically low friction, low adhesion, and low wear of the film. Since the coating allows machining without lubricants and essentially eliminates metal burrs, this approach can reduce the environmental impact of micro-machining processes and offers greatly improved performance for micro and meso-scale manufacturing applications.     

TiCN and metallic coatings for corrosion protection of separator plates in MCFCs

Stainless steel 304 substrates were coated with different materials in order to find a suitable coating material for corrosion protection of separator plates in molten-carbonate fuel cells (MCFCs). Five titanium carbonitride coatings differing in composition and morphology and a titanium monoxide coating were deposited with chemical vapour deposition techniques. Also double-layer coatings of TiN/Au and TiN/Ni were prepared. The coatings were tested on their corrosion protection of separator plates in four different environments: under MCFC-cathode or anode gas, at load or at open circuit conditions. The corrosion behaviour was characterized using cyclic voltammetry. Corrosion rates were determined with electrochemical methods and cross-section analyses of corrosion layers. Titanium nitride coatings showed the best corrosion protection. The titanium carbide and titanium monoxide coating showed respectively less and no protection. The thin gold and Ni-coatings were unstable. Under cathode gas, the most important corrosion protection is given by keeping the cell at load, and then a titanium nitride coating might provide lifetime protection. Under anode gas, corrosion is most severe at load conditions. A titanium nitride coating also gives corrosion protection, but not enough for lifetime protection.     

Influences of bias voltage on properties of TiAl-doped DLC coatings synthesized by cathodic arc evaporation

In this work, the combinations of TiAl-doped DLC (Diamond-like Carbon) and TiAlN/TiN double-layered films were designed to deposit on the tool steels using cathodic arc evaporation in a single process. The economic advantage in depositing the combined coating in one production scale PVD coating system is of practical importance. The TiAl-doped DLC as lubricant coatings were synthesized with TiAl-target arc sources to emit ion plasma to activate acetylene reactive gases. Scanning electron microscopy (SEM), Auger electron spectroscopy (AES), micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) techniques were employed to analysis the microstructure properties of TiAl-doped DLC coatings. Vicker's and tribometer tester were used to measure the mechanical properties of TiAl-doped DLC coatings. The results show that the TiAl-doped DLC coatings retained lower friction coefficient at approximately 0.15 during the steady state sliding. The lubricity and wear resistance of TiAl-doped DLC coatings is then demonstrated to potentially be applied to the cutting tools with no lubricants.     

Microstructure,mechanical properties and machining performance of spark plasma sintered Al2O3–ZrO2–TiCN nanocomposites

The effect of addition of nanocrystalline ZrO₂ and TiCN to ultrafine Al₂O₃ on mechanical properties and microstructure of the composites developed by spark plasma sintering (SPS) was investigated. The distribution of the nanoparticles was dependent on their overall concentration. Maximum hardness (21 GPa) and indentation toughness (5.5 MPa m^1/2) was obtained with 23 vol% nanoparticles, which was considered as the optimum composition. The Zener pinning criteria were also satisfied at this composition with grain size of the restraining nanoparticles ～63–65 nm. Hardness of the composites follows the rule of mixtures; crack deflection and crack arrest by nanoparticles at grain boundaries along with mixed fracture mode led to high toughness in the nanocomposites. Cutting tool inserts were developed by SPS with the optimized composition and their machining performance was compared with commercial alumina based inserts. Increased toughness in the nanocomposite inserts reflects in the machining performance as the tool life improves drastically compared to that of the commercial inserts at high cutting speeds ≥500 m min^?1. This was attributed to differences in their failure modes; the commercial inserts fail catastrophically by fracture due to their low toughness whereas the nanocomposite inserts reach the tool failure criteria by crater wear at all machining conditions.     

Friction behavior of TiN–MoS2/PTFE composite coatings in dry sliding against SiC

To improve the dry friction behavior of traditional hard coatings, MoS₂/PTFE lubricating coatings were prepared on the PVD TiN-coated cemented carbide using spray method. The influences of MoS₂/PTFE lubricating coatings on the primary characteristics of TiN coatings were investigated. Reciprocating sliding tests were carried out with the TiN–MoS₂/PTFE coated specimen (T-M-P) under dry sliding conditions, and the tribological behaviors were compared to those of the TiN-coated one (T-N). The test results indicated that the adhesion force of coatings with substrate for T-M-P specimen increased, the surface micro-hardness, roughness and friction coefficient significantly decreased. Meanwhile, the surface adhesions and abrasion grooves of T-M-P specimen were reduced, and the main wear forms of T-M-P were abrasion wear and coating delamination. The MoS₂/PTFE lubricating coatings can be considered effective to improve the friction properties of traditional hard coatings.     

Friction and wear behavior of microwave sintered Al2O3/TiC/GPLs ceramic sliding against bearing steel and their cutting performance in dry turning of hardened steel

An Al₂O₃/TiC/GPLs (ATG) composite ceramic tool material was fabricated by microwave sintering. The tribological properties of ATG during sliding against GCr15 bearing steel were studied, to investigate the effects of sliding speed and normal load on the friction coefficient and wear rate. In addition, the cutting performance of ATG tools for machining of hardened alloy 40Cr steel was experimentally studied and compared with those of commercial tools. The results showed that the added graphene platelets enhanced the wear resistance and reduced the friction coefficient of the tool material. Furthermore, upon adding graphene platelets, the ability of the tools to resist breakage and their cutting depth improved. The cutting length of the microwave- sintered ATG ceramic tools was approximately 125% higher than that of hot-pressed ceramic tools and 174% higher than that of cemented carbide tools.     

Substrate effect on wear resistant transition metal nitride hard coatings: Microstructure and tribo-mechanical properties

Four types of different hard transition metal nitrides (TMN:ZrN, CrN, WN and TiN) coatings were deposited on Si (100) and 316LN stainless steel substrates using DC magnetron sputtering. A comprehensive study of microstructure and substrate dependent tribo-mechanical properties of TMN coatings was carried out. Higher hardness (H) and elastic modulus (E) were obtained for WN (H=40 GPa and E=440 GPa) and TiN (H=30 GPa and E=399 GPa) coatings. This is related to the formation of (100) and (111) preferred orientations in WN and TiN coatings, respectively. However, the less hardness and elastic modulus were obtained for ZrN and CrN coatings where (200) orientation is preferred. Remarkably, low friction coefficient (0.06–0.57) and higher wear resistance in the coatings deposited on steel substrates are directly associated with the higher resistance to plastic deformation (H³/E²) and the presence of intrinsic compressive stress. Three body wear modes enhanced the friction coefficient (0.15–0.62) and the wear rate in the coatings deposited on Si substrates. This is primarily associated with low fracture toughness of brittle single crystalline Si (100) substrates. Steel-on-steel contact was dominated in ZrN/steel sliding system. This occurs due to the severe adhesive wear mode of steel ball, whereas, the abrasive wear modes were attained for the CrN, WN and TiN coatings sliding against steel balls.     

Analytical transmission electron microscopy observations on the stability of TiCN in electrically conductive α-β SiAlON/TiCN composites

Coating of α-β SiAlON granules with TiCN powder led to a continuous 3D electrically conductive network formation. Here, the stability of TiCN grains following gas pressure sintering (GPS) and its effect on the electrical properties of an α-β SiAlON/TiCN composite were analytically investigated by using transmission electron microscopy (TEM) based techniques. In situ formation of nano-sized SiC grains adjacent to TiCN and α-β SiAlON grains were observed. These SiC grains may play a role on the high electrical conductivity of α-β SiAlON/TiCN composite. Ti:C:N ratios from TiCN grains along the network showed that TiCN grains did not preserve their initial composition after sintering. Finally, Ti diffusion from TiCN grains into α-β SiAlON and triple junction phases was observed. The incorporation of Ti into the SiAlON crystal lattices contributes to the high electrical conductivity of α-β SiAlON/TiCN composite.     

In Situ Preparation of Si3N4/SiC Nanocomposites for Cutting Tools Application

Silicon nitride–silicon carbide nanocomposite has been prepared by an in situ method that utilizes the formation of SiC nanograins by carbothermal reduction of intentionally added fine SiO₂ during the sintering process. The mean value of room-temperature four-point bending strength is 675 MPa with the Weibull modulus of 6.4 and an indentation fracture toughness of 7.4 MPa·m^1/2. A significantly enhanced creep resistance was achieved by the incorporation of SiC nanoparticles into the matrix up to 1400°C. The tribological properties of the material were tested using a ball-on-disk configuration and showed a friction coefficient of about 0.7. The cutting inserts machined from this composite had three times longer lifetime compared with those available on the market. On the other hand, the scatter of results is much larger compared with those measured for the commercial inserts.     

Effects of tool coating materials and coating thickness on cutting temperature distribution with coated tools

Coated tools are currently widely used tool technology in machining. The influence of tool coating on heat transfer has become an active field of research enjoying constantly increasing attention in the field of machining. This paper is devoted to the cutting temperature in machining H13 hardened steel with monolayer coated tools (TiN, TiAlN, and Al₂O₃) and multilayer coated tools (TiN/TiC/TiN and TiAlN/TiN). Equivalent composite thermal conductivity and thermal diffusivity of multilayer coated tools were calculated using the equivalent approach. The established heat transfer analytical models estimated coating temperature in turning. The effect of tool coating in steady and transient heat transfer was studied, as well as the cutting temperature distribution. It reveals that the tool coating material and coating thickness can influence the cutting temperature distribution of coated tool. Thermal conductivity of coating material affects the steady cutting temperature distribution, and thermal diffusivity of coating material affects the transient cutting temperature distribution of coating tools.