Numerous studies are available regarding the effect of PVD and CVD coatings on cutting tools (inserts), cutting parameter optimization, and the application of the minimum quantity lubrication on the reduction of cutting tool wear and the improvement in surface quality of the machined parts. However, there still exists the deficiency of the comprehensive analysis of improving machining performance by suppressing high frequency vibration (micro-vibration) at the cutting edge due to the random nature of cutting force. The present study aims to mitigate this challenge of suppressing micro-vibration by applying the high dynamic stiffness multilayered Cu: CuCN<inf>x</inf> nanocomposite coating at the close proximity of cutting edge (in between the cutting insert and shim) by synthesizing the Cu:CuCN<inf>x</inf> coating on conventional cemented carbide (WC-Co) square shims. The primary objective of this study was to experimentally investigate the effect of Cu:CuCN<inf>x</inf> coating's morphology on machining performance. Coating morphology was characterized by the total coating thickness and total number of alternative Cu and CuCN<inf>x</inf> layers in a certain coating thickness. Machining performance was evaluated based on the criteria of cutting tool life and machined part's surface quality. External longitudinal turning operations of SS2541-03 alloy steel (34CrNiMoS6) material with rough cutting parameters and wet condition (using cutting fluid) were adopted for evaluating machining performance. Three different Cu:CuCN<inf>x</inf> coating series- A, B and C were synthesized by means of a double cathode Reactive High-Power Impulse Magnetron Sputtering (R-HiPIMS) deposition system. Coatings of series-A were deposited on steel disc substrates, and were used to evaluate the Cu:CuCN<inf>x</inf> nanocomposite coating's mechanical properties as a function of total number of Cu and CuCN<inf>x</inf> layers in a fixed coating thickness. Mechanical properties of the coatings were investigated by Vickers micro-indentation, and the damping loss factor of the coating was evaluated on the basis of indentation creep measurements under room temperature. Results from the analysis with coating series A demonstrated that the maximum elastic modulus, loss factor and loss modulus values of the coating was obtained when the ratio of total number Cu and CuCN<inf>x</inf> layers to coating thickness (n/h) is 0.6. However, the hardness, H/E and H³/E² values were observed to be increasing with increasing number of total layers. The coating with optimum mechanical properties exhibited the highest loss modulus of 2.85 ± 0.03 GPa confirming the high dynamic stiffness of Cu:CuCN<inf>x</inf> nanocomposite. Coated shims prepared with coating series- B and C were used to evaluate the effect of total number of Cu and CuCN<inf>x</inf> layers and the effect of total coating thickness on the machining performance, respectively. From the turning tests with conventional shim and coated shims it was evident that the coated shim with 200 μm Cu:CuCN<inf>x</inf> coating (sample C3) increased the cutting tool life by at least 50 % and reduced the machined workpiece's surface roughness by 15 %. For all turning tests, the thicknesses of coated shims and corresponding conventional uncoated shim were kept constant. The maximum error between the experimental and predicted values of the mechanical properties of coating series-B was found to be less than 10 %Moreover, in case of 200 μm Cu:CuCN<inf>x</inf> coating containing 150 layers of Cu and CuCN<inf>x</inf> phases, the coated shim (sample B3) was able to increase the cutting tool life by at least 167 %, and the machined workpiece's average surface roughness was reduced by 10 %. Analysis of the acquired vibration signals during turning tests, indicated that the cutting tool life was prominently affected by the higher frequency vibration (>7000 Hz) at the tool's cutting-edges. It was observed that with the application of 200 μm Cu:CuCN<inf>x</inf> coating in coated shim, the root mean squared (RMS) vibration energy in overall frequency range (0 to 30,000 Hz) was reduced by 40 %. From material and mechanical characterization, it was postulated that the primary vibration energy dissipation mechanisms of the multilayered nanocomposite coating are the interface frictional energy loss between the alternative Cu and CuCN<inf>x</inf> layers and the intrinsic damping due to grain boundary sliding in CuCN<inf>x</inf> layers.

High-power impulse magnetron-sputtering thick metal/carbon-nitride-doped metal-matrix multilayer nano-composite coating can be applied to cutting-tool holder components to improve cutting insert's life. One of the challenges of such an add-on solution is the poor adhesion between the thick coating and the hard alloy substrate, such as WC-Co shim. This work presents a study on WC-Co substrate surface preparation methods for HiPIMS coating and its adhesion improvement. Three mechanical surface pretreatment methods were investigated: machining (grinding), diamond polishing, and grit blasting. White-light interferometry was used for substrate surface texture measurement before and after pretreatment. It was demonstrated that, compared to machining and diamond polishing, grit blasting can significantly improve the interface adhesion between the similar to 200 mu m-thick Cu:CuCNx coating and WC-Co shim. Grit blasting was also found to be beneficial for improving the cutting insert's life in the external turning process. In turning tests, the coating lifetime for grit-blasted shim was more than 90 min, whereas the coating lifetimes for machined shim (conventional shim) and diamond-polished shim were similar to 85 min and similar to 70 min, respectively. Further, by comparing the HiPIMS gradient chromium pre-layer between the coating and substrate for the different shims, the study also explained that the quasi-isotropic surface texture of grit-blasted shim is more advantageous for coating-substrate interface adhesion.

This paper reports an industry standard monolithic 555-timer circuit designed and fabricated in the in-house silicon carbide (SiC) low-voltage bipolar technology. The paper demonstrates the 555-timer ICs characterization in both astable and monostable modes of operation, with a supply voltage of 15 V over the wide temperature range of 25 to 500°C. Nonmonotonictemperature dependence was observed for the 555-timer IC frequency, rise-time, fall-time, and power dissipation.

A thick 400-micron amorphous carbon nitride (a-CNX ) coating material was synthesized by means of plasma-enhanced chemical vapor deposition process. High-power impulse magnetron sputtering technique was used to sputter a pure graphite target plate in reactive argon (Ar), nitrogen (N2 ) and acetylene (C2 H2 ) environment for depositing the omposite coating. Structural and chemical/elemental composition of the a-CNX  composite material was investigated by field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and micro-Raman spectroscopy. The rootmean-square surface roughness (Sq ) and structure were estimated by atomic force microscopy. Mechanical properties such as hardness and Young’s modulus (Oliver–Pharr method) at room temperature were characterized by Vickers microindentation test. Operational temperature test of the deposited a-CNX  coating reveals that it can withstand up to 400 C without cracking. An inverted shaker test, based on central impedance method, was adopted to investigate the dynamic damping property of the coating material, and it was found that the first bending mode damping lossfactor of the reported a-CNX  coating is 0.015 ±  0.001 and corresponding loss modulus (Young’s modulus multiplied by lossfactor) is 0.234 ±  0.011 GPa.

Nanostructured Cu:CuCN_x composite coatings with high static and dynamic stiffness were synthesized by means of plasma-enhanced chemical vapor deposition (PECVD) combined with high power impulse magnetron sputtering (HiPIMS). Scanning electron microscope (SEM) images and energy-dispersive X-ray spectroscopy (EDS) mapping from cross-sectioned samples reveals a multi-layered nanostructure enriched in Cu, C, N, and O in different ratios. Mechanical properties of the coatings were investigated by Vickers micro-indention and model tests. It was observed that copper inclusions as well as copper interlayers in the CN_x matrix can increase mechanical damping by up to 160%. Mechanical properties such as hardness, elastic modulus and loss factor were significantly improved by increasing the discharge power of the sputtering process. Moreover the coatings loss modulus was evaluated on the basis of indentation creep measurements under room temperature. The coating with optimum properties exhibited loss modulus of 2.6 GPa. The composite with the highest damping loss modulus were applied on the clamping region of a milling machining tool to verify their effect in suppressing regenerative tool chatter. The high dynamic stiffness coatings were found to effectively improve the critical stability limit of a milling tool by at least 300%, suggesting a significant increase of the dynamic stiffness.

Vibration phenomena are a main consideration during the material removal operation, as it has prominent effects on the product quality, cutting tool life, and productivity of that machining operation. Within the context of machining performance, role of enhanced stiffness and damping on the dynamic behaviour of machining systems such as turning and milling is well established. In this experimental analysis, investigations have been conducted for identifying the natural characteristics and dynamic responses of a milling process with the application of a novel carbon based (CNx) nano-composite damping material. TheCNx material has been applied into the joint interface of a workholding device with adaptive dynamic stiffness. Prior investigations of this material, produced by theplasma enhanced chemical vapor (PECVD) process, showed inherent damping capacity via interfacial frictional losses of its micro-columnar structures. For thisstudy, natural characteristics of the workholding system have been characterized bythe modal impact testing method. Dynamic responses during the machining processhave been measured through the vibration acceleration signals. The ultimate objective of this study is to comprehend the potentiality of CNx coating material forimproving machining process performance by analyzing the frequency response functions and measured vibration signals of the investigated milling process with varying stiffness and damping levels.