The Tool Life and Coating-Substrate Adhesion of AlCrSiN-Coated Carbide Cutting Tools Prepared by LARC with Respect to the Edge Preparation and Surface Finishing

Composite Materials with Nanoscale Multilayer Architecture Based on Cathodic-Arc Evaporated WN/NbN Coatings

Hard nitride coatings are commonly employed to protect components subjected to friction, whereby such coatings should possess excellent tribomechanical properties in order to endure high stresses and temperatures. In this study, WN/NbN coatings are synthesized by using the cathodic-arc evaporation (CA-PVD) technique at various negative bias voltages in the 50-200 V range. The phase composition, microstructural features, and tribomechanical properties of the multilayers are comprehensively studied. Fabricated coatings have a complex structure of three nanocrystalline phases: β-W2N, δ-NbN, and ε-NbN. They demonstrate a tendency for (111)-oriented grains to overgrow (200)-oriented grains with increasing coating thickness. All of the data show that a decrease in the fraction of ε-NbN phase and formation of the (111)-textured grains positively impact mechanical properties and wear behavior. Investigation of the room-temperature tribological properties reveals that with an increase in bias voltage from -50 to -200 V, the wear mechanisms change as follows: oxidative → fatigue and oxidative → adhesive and oxidative. Furthermore, WN/NbN coatings demonstrate a high hardness of 33.6-36.6 GPa and a low specific wear rate of (1.9-4.1) × 10-6 mm3/Nm. These results indicate that synthesized multilayers hold promise for tribological applications as wear-resistant coatings.

Preparation of Cemented Carbide Insert Cutting Edge by Flexible Fiber-Assisted Shear Thickening Polishing Method

Reasonable cutting edge preparation can eliminate microscopic defects and improve the performance of a cutting tool. The flexible fiber-assisted shear thickening polishing method was used for the preparation of cemented carbide insert cutting edge. The influences of the polishing angle and polishing speed on the cutting edge preparation process were investigated, and the cutting edge radius and K-factor were employed as evaluation indexes to evaluate the edge shape. A prediction model of the cutting edge radius was also established using the mathematical regression method. The results show that the polishing angle has a more significant effect on the cutting edge radius. The cutting edge preparation efficiency is the highest under the polishing angle of 10°, and the cutting edge radius increased from the 15 ± 2 μm to 110 ± 5 μm in 5 min. The cutting edge shape can be controlled by adjusting the polishing angle, and the K-factor varies from 0.14 ± 0.03 to 0.56 ± 0.05 under the polishing angle (from -20° to 20°). The polishing speed has a less effect on the cutting edge radius and shape, but increasing the polishing speed within a certain range can improve the efficiency of cutting edge preparation. The flank face roughness decreased from the initial Ra 163.1 ± 10 nm to Ra 5.2 ± 2 nm at the polishing angle of -20°, which is the best polishing angle for the flank face surface roughness. The ANOVA method was employed to evaluate the effective weight of the polishing angle and polishing speed on preparation efficiency. The polishing angle (86.79%) has the more significant influence than polishing speed (13.21%) on the cutting edge preparation efficiency. The mathematical regression method was used to establish the model of the prediction of the cutting edge radius with polishing angle and speed, and the models were proved rationally. The results indicate that the FF-STP is an effective method for the high consistency preparation of cemented carbide insert cutting edge.

Effect of Laser Heating on the Life of Cutting Tools Coated with Single- and Multilayer Coatings Containing a TiN Layer

This study proposes a novel use of laser heating to increase the adhesion between coatings fabricated by low-temperature PVD and replaceable cemented carbide cutting inserts, thus extending the life of these cutting tools in the machining of difficult-to-machine materials. Our previous studies conducted on CVD coatings showed that these coatings had higher adhesion due to a much higher process temperature. However, taking into account the fact that PVD coatings have better technological properties (e.g., lower structure porosity, higher hardness, and better tribological properties) than CVD coatings, it is fully justified to investigate ways of improving the PVD coating adhesion to the substrate. In this study, replaceable cutting inserts with different hard coatings of titanium nitride were used. Laser heating was conducted with different power densities. The adhesion strength of the tested coatings was determined via vibration spectrum analysis. In addition, 2D surface imaging, scanning electron microscopy, and X-ray fluorescence spectrometry were employed to examine the coatings after laser heating. A significant increase in the adhesion of single-layer (TiN) and double-layer (TiCN + TiN) coatings to the cemented carbide substrate, together with increased tool life, was observed after heating the samples with 40% of the maximum laser power. The application of a multilayer coating containing thermal shock-sensitive (TiAlSi) N did not increase the tool life. This paper attempts to interpret the obtained results.

Development of DLC-Coated Solid SiAlON/TiN Ceramic End Mills for Nickel Alloy Machining: Problems and Prospects

The study is devoted to the development and testing of technological principles for the manufacture of solid end mills from ceramics based on a powder composition of α-SiAlON, β-SiAlON, and TiN additives, including spark plasma sintering powder composition, diamond sharpening of sintered ceramic blanks for shaping the cutting part of mills and deposition of anti-friction Si-containing diamond-like carbon (DLC) coatings in the final stage. A rational relationship between the components of the powder composition at spark plasma sintering was established. The influence of optimum temperature, which is the most critical sintering parameter, on ceramic samples’ basic physical and mechanical properties was investigated. DLC coatings’ role in changing the surface properties of ceramics based on SiAlON, such as microrelief, friction coefficient, et cetera, was studied. A comparative analysis of the efficiency of two tool options, such as developed samples of experimental mills made of SiAlON/TiN and commercial samples ceramic mills based on SiAlON, doped with stabilizing additives containing Yb when processing nickel alloys (NiCr20TiAl alloy was used as an example). DLC coatings’ contribution to the quantitative indicators of the durability of ceramic mills and the surface quality of machined products made of nickel alloy is shown.

An Investigation of the High-Frequency Ultrasonic Vibration-Assisted Cutting of Steel Optical Moulds

Ultrasonic vibration-assisted cutting (UVAC) has been regarded as a promising technology to machine difficult-to-machine materials such as tungsten carbide, optical glass, and hardened steel in order to achieve superfinished surfaces. To increase vibration stability to achieve optical surface quality of a workpiece, a high-frequency ultrasonic vibration-assisted cutting system with a vibration frequency of about 104 kHz is used to machine spherical optical steel moulds. A series of experiments are conducted to investigate the effect of machining parameters on the surface roughness of the workpiece including nominal cutting speed, feed rate, tool nose radius, vibration amplitude, and cutting geometry. This research takes into account the effects of the constantly changing contact point on the tool edge with the workpiece induced by the cutting geometry when machining a spherical steel mould. The surface morphology and surface roughness at different regions on the machined mould, with slope degrees (SDs) of 0°, 5°, 10°, and 15°, were measured and analysed. The experimental results show that the arithmetic roughness Sa of the workpiece increases gradually with increasing slope degree. By using optimised cutting parameters, a constant surface roughness Sa of 3 nm to 4 nm at different slope degrees was achieved by the applied high-frequency UVAC technique. This study provides guidance for ultra-precision machining of steel moulds with great variation in slope degree in the pursuit of optical quality on the whole surface.

Influence of DLC Coatings Deposited by PECVD Technology on the Wear Resistance of Carbide End Mills and Surface Roughness of AlCuMg2 and 41Cr4 Workpieces

The primary purpose of this work was to study the effectiveness of using diamond-like coatings (DLC) to increase the wear resistance of carbide end mills and improve the surface quality of the processed part when milling aluminum alloy and low-carbon steel. The functional role of forming an adhesive sublayer based on (CrAlSi)N immediately before the application of the external DLC film by plasma-enhanced chemical vapor deposition (PECVD) technology in the composition of a multicomponent gas mixture containing tetramethylsilane was established in the article. The article shows the degree of influence of the adhesive sublayer on important physical, mechanical, and structural characteristics of DLCs (hardness, modulus of elasticity, index of plasticity, and others). A quantitative assessment of the effect of single-layer DLCs and double-layer (CrAlSi)N/DLCs on the wear rate of end mills during operation and the surface roughness of machined parts made of aluminum alloy AlCuMg2 and low-carbon steel 41Cr4 was performed.

Wear Resistance and Titanium Adhesion of Cathodic Arc Deposited Multi-Component Coatings for Carbide End Mills at the Trochoidal Milling of Titanium Alloy

The work was devoted to the study of the effectiveness of the application of multi-component coatings, TiN–Al/TiN, TiN–AlTiN/SiN, and CrTiN–AlTiN–AlTiCrN/SiN, obtained by cathodic arc deposition to increase the wear resistance of 6WH10F carbide end mills in trochoidal milling of titanium alloy. The surface morphology of the tool with coatings was studied using scanning electron microscopy, and surface roughness texture was estimated. Microhardness and elastic modulus of the coated carbide tool surface layer were determined by nanoindentation. The process of sticking titanium to the working surface of the tool and quantitative evaluation of end mill wear with multi-component coatings at the trochoidal strategy of milling titanium alloy was studied. The CrTiN–AlTiN–AlTiCrN/SiN coating showed the maximum value of the plasticity index at the level of 0.12. The maximum effect of reducing the wear rate was achieved when using a tool with a CrTiN –AlTiN–AlTiCrN/SiN coating when the operating time to failure of end mills was increased by 4.6 times compared to samples without coating, by 1.4 times compared with TiN–Al/TiN coating and 1.15 times compared with TiN–AlTiN/SiN coating.