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Ti(C,N)-based cermets with a CoCrFeMnNi high-entropy alloy (HEA) binder phase were coated via chemical vapor deposition (CVD). The influence of the HEA-bonded cermet substrate on the microstructure, orientation, adhesion, and high temperature frictional wear performance of the CVD coating was investigated. The results indicate that the HEA binder phase inhibits the growth of cermet grains and provides more nucleation sites for the coating. Thus, the coating on the HEA-bonded cermet has a smaller grain size. The substitution of HEA for the Ni binder phase increases the entropy value of the cermet system, resulting in a decrease in free energy. In the early stage of CVD, the gas atoms adsorbed on the solid surface with low free energy are in a more stable thermodynamic state, which enhances the adhesion strength between the coating and substrate. During high temperature frictional wear, the friction coefficient of the coating on Ni-bonded cermet is less than that of the coating on HEA-bonded cermet because of iron oxide lubricating films. However, the wear rate exhibits a reverse trend. The coating on the HEA-bonded cermet has the best wear resistance due to small grain size, superior hardness and excellent adhesion strength. The wear forms present in the CVD coatings are abrasive wear, adhesive wear and oxidation wear. [ABSTRACT FROM AUTHOR]

Abstract The development of new coated cemented carbide tool grades, based on grain refining and the unidirectional orientation of crystals in the coating layer, allows this material to withstand the severe tribological conditions imposed in hard turning. Previously, this was only possible using PCBN or oxide ceramic tool materials. The aim of this research was to determine the limiting conditions for two coated cemented carbide grades (with MT CVD and PVD coatings) aimed at allowing them to withstand at least a machining time of 15 min in the turning of hardened steels, considering the cutting parameters usually adopted for PCBN tools. Turning experiments were performed on AISI 4340, AISI 52100 and AISI D2 hardened steels, and the worn cutting edges were analyzed using focus variation microscopy (FVM) applying the three-dimensional wear parameters. The use of the PVD-coated cemented carbide grade was feasible in the case of AISI 4340 steel with a level of hardness up to 55 HRC, allowing a machining time longer than 30 min. For AISI 52100 and D2 steels, feasibility was only observed with hardness levels up to 50 and 45 HRC, respectively. Interestingly, in these cases, longer machining times were achieved using the MT CVD-coated cemented carbide grade. Wear and consequent coating layer deterioration were found to be the limiting factors for tool life, and the three-dimensional wear parameters allowed these to be identified. The results indicated the appropriate limiting conditions for the application of coated cemented carbide grades in hard turning as a function of the steel microstructure and level of hardness. Highlights • Application of coated cemented carbide tools grades in turning of hardened steels. • Application of focus variation microscope (FVM) and volumetric wear parameters. • Criterion for tool life based on volumetric wear parameter. • Tool life is strongly associated with tools coating deterioration. • Coating deposition technique and steel microstructure influence the tool life. [ABSTRACT FROM AUTHOR]

Polycrystalline diamond coatings have been grown on cemented carbide WC-6% Co substrates with different aspect ratios by microwave plasma CVD in CH 4 /H 2 gas mixtures. Special plateholder with holes for group growth has been used to protect the edges of the substrates from non-uniform heating due to the plasma edge effect. The difference in heights Δh of the substrates and plateholder, and its influence on the diamond film mean grain size, growth rate, phase composition and stress was investigated. Diamond growth rate of 0.3–1 μm/h and compressive stress of 2.2–2.5 GPa, respectively were determined in the optimal Δh region. The substrate temperature range of 740–760 °C, within which uniform diamond films are produced with good adhesion, is determined. The diamond-coated samples produced at optimized process conditions exhibited a reduction of cutting force and wear resistance by a factor of two, and increase of cutting path length up to 8150 m or by 4.3 times upon turning А390 Al-Si alloy as compared to performance of uncoated tools. Prime novelty Polycrystalline diamond coatings with uniform structure and thickness distribution are grown by microwave plasma CVD (MPCVD) on WC-6% Co substrates using an optimized pocket-type substrate holder. Edge effect during MPCVD on high substrates (height/diameter > 0.1) was suppressed. Influence of distance between the substrate holder and substrate surface on deposition temperature and other parameters was investigated. Cutting force and wear rate of the coated samples upon cutting of Si-Al abrasive alloy were twice less than that of uncoated WC-6% Co. [ABSTRACT FROM AUTHOR]

Dry-ice blasting is applied in atmospheric plasma spray process with an aim to improve the properties of Cr2O3 coatings and save the cost. Microstructure, the tensile adhesive strength and the wear resistance of plasma-sprayed Cr2O3 coatings without and with the treatment of dry-ice blasting were compared. The results indicate that dry-ice blasting has a significant effect on the porosity of Cr2O3 coating. After the treatment of dry-ice blasting, the porosity of Cr2O3 coating decreases from 6.6±1.1% to 2.0±0.1% and a noticeable improvement in the adhesion between the coating and 25CrMo4 substrate has been obtained from 13±2MPa to 46±5MPa. They could be attributed to the sublimation effect of dry-ice pellets on the evaporated Cr and the cleaning effect of dry-ice blasting on the coated substrate. The dry-ice blasted coating was more wear resistant than that deposited without dry-ice blasting. [ABSTRACT FROM AUTHOR]

Abstract: Beam-assisted deposition of wear-resistant coatings on complex shaped dielectric products is used as a source of slow metal atoms and fast gas molecules with coinciding trajectories of their movement from a common emissive grid to the products. This allows keeping the ratio of metal atom flow density to that of fast molecules constant as well as uniformity of deposited coating properties at the whole surface of the planetary rotating inside vacuum chamber products, including their cavities. The fast molecules are produced due to charge-exchange collisions of ions accelerated by potential difference between a plasma emitter inside the source and secondary plasma inside the chamber. The plasma emitter is produced by glow discharge with confinement of electrons in an electrostatic trap formed by a cold hollow cathode and an emissive grid the latter being negative to both the cathode and the chamber. Metal vapor is produced due to sputtering of a target placed at the bottom of the hollow cathode by ions from the plasma emitter accelerated by a negative bias voltage 2kV. [Copyright &y& Elsevier]

Abstract: The use of surface texturing on the rake face of a tool can modify the tribological phenomena present at the chip-tool interface. Many different wear mechanisms, including abrasive wear, occur at the tool during machining. The presence of hard phases in the workpiece material, as well as hard particles removed from the tool, can generate abrasive wear on the tool surfaces. The objective of this work is to study the abrasive wear resistance of micro-textured tools in comparison to conventional (commercial) cutting tools. Square cemented carbide inserts containing a three-layered coating (TiCN–Al2O3–TiN) were textured using two different linear patterns, perpendicular and parallel to the direction of the chip movement. Microabrasion and machining tests on both textured and commercial tools were carried out. Turning tests were carried out for ABNT/AISI 1050 steel under severe cutting conditions with overhead application of cutting fluid. In order to simulate the abrasive wear mechanism that can occur on the tool surface, a free ball microabrasion test was used under a suspension of silicon carbide particles and distilled water. The abrasive wear mechanisms were observed using SEM. The micro-scale abrasive wear resistance of laser micro-textured cement carbide tools was compared to untextured tools. For the turning tests, texturing increased the tool life, which was determined when the wear at the tool flank achieved a specified value. On the other hand, for the microabrasion tests, laser texturing resulted in a pronounced increase in the coating wear rate. This fact was connected to the decrease of coating hardness caused by laser texturing. Therefore, the increase of tool life in the turning tests was not related to a reduction of abrasive wear on the tool flank. Probably, it was caused by other tribological conditions that were not represented in microabrasion tests, for example: the presence of cutting fluid in the environment and elevated contact temperatures. [Copyright &y& Elsevier]

Abstract: This work discusses the performance of multilayer coatings in dry cutting fiber reinforced polymers. The cutting tests were performed on unidirectional carbon/epoxy and glass/epoxy specimens with 45° fiber orientation using both Chemical Vapor Deposited (CVD) and Physical Vapor Deposited (PVD) multilayer coatings with neatly different composition, grain size and substrate-to-coating adherence. CVD TiCN/Al2O3/TiN with low adherence (CVD-L), PVD TiAlN/AlCrO with medium adherence (PVD-M) and PVD TiN/TiAlN with high adherence (PVD-H) inserts were considered for experimental tests. Scanning Electron Microscope (SEM) was utilized to characterize the flank wear patterns. The apparent friction coefficient dealing with the material removal process was deduced from cutting forces measured using Kistler piezoelectric dynamometer. The adhesive frictional signature was examined on both new and worn inserts through series of micro-scratch tests using Atomic Force Microscope (AFM). While abrasion mechanisms dominate the flank wear upon all inserts, the abrasion mode transforms from mild to severe depending upon coating layer characteristics. Regular inspections on the worn face demonstrated that the fail of first-deposited coating layer characterizes a threshold point from which the insert behavior drastically changes. The change in forces and friction tendencies' slopes beyond threshold proves that fiber phase abrasiveness dominates wear mechanisms irrespective to coating type. [Copyright &y& Elsevier]

Al-rich phases are often recommended as potential coating candidates for TiAl alloys and their application as a turbine blade material in aero engines. As high wear resistance is also required for this application, the tribological properties of Al-rich phases need to be investigated with a focus on the influence of temperature. Therefore, a comparative investigation of the dry sliding wear behavior of the uncoated and aluminized Ti–48Al–2Cr–2Nb TiAl alloy was conducted between room temperature and 600 °C in air. While the uncoated TiAl alloy suffers from successively increasing wear rates with increasing temperature, the aluminized alloy shows lower wear rates up to 400 °C. However, barely any positive influence on the required wear protection can be observed at 600 °C due to partial failure of the coating. Wear mechanisms of both the uncoated and aluminized samples are characterized by high material transfer to the counterpart material, the Ni-based alloy IN718. This phenomenon is caused by the tendency for strong adhesive bonding between the two metallic counterparts and becomes even more pronounced with increasing temperature. • Wear rates of the uncoated TiAl alloy increase with increasing temperature. • Material transfer from the TiAl alloy to the IN718 counterpart occurs already at RT. • Aluminizing leads to lower wear rates up to 400 °C due to a higher surface hardness. • Partial coating failure occurs at 600 °C leading to highly increased wear rates. • Aluminizing can also improve the oxidation resistance of TiAl turbine blades. [ABSTRACT FROM AUTHOR]

The machining of advanced materials is challenging the tooling technology. To cope this, new cutting materials and geometries are developed. In this case, four types of silicon nitride based ceramics are investigated after coating with CVD-diamond for the use as ceramic end mills. To assess the wear resistance, model wear tests and damage evaluation were carried out and evaluated. After subsequent summary of the results, ceramic and cemented carbide substrate were selected for milling of glass and carbon fiber reinforced plastic (GFRP/CFRP) The determined force distribution and wear properties of the tools are presented and discussed. The diamond coated substrates are qualified by their wear profile and the measured constant cutting forces for use in the machining of GFRP/CFRP. Finally, the crack formation progress for diamond coated silicon nitrides when machining glass and carbon fiber reinforced plastics was demonstrated. [ABSTRACT FROM AUTHOR]