Providing advanced coating solutions for high-speed dry machining applications is gaining importance by the day especially with the increasing employment of difficult-to-machine materials in niche areas. Taking into account the recent demands in developing such coatings, in the present study, a novel low-friction coefficient nanocomposite coating: CrAlSiN/gradient (G)-CrAlSiCN was developed which can be used in high-speed or dry machining applications. Initially, CrAlSiN nanocomposite coating and carbon incorporated CrAlSiN coating were deposited separately using the cylindrical cathodic arc physical vapor deposition (PVD) technique. The as-deposited films were comprehensively analyzed to determine their adhesion strength, phase composition, sliding wear properties (friction coefficient), hardness, and tool life. Preliminary observations revealed that the films did not show evidence of diamond-like carbon (DLC) formation (from Raman analysis). Further, an increase in the carbon content led to a steep decrease in the adhesion strength. This result persuaded a study on developing a novel coating with gradient carbon architecture that would retain the properties of a nanocomposite whilst supporting the nanocomposite underlayer by reducing the coefficient of friction. In comparison with the CrAlSiN nanocomposite coating and a standard DLC coating, the novel gradient carbon coating showed superior tribological properties along with better tool life. This study marks the first such attempt at studying the influence of carbon incorporation to the CrAlSiN nanocomposite coating on improving the overall mechanical and tribological properties of the coating architecture (CrAlSiN/G-CrAlSiCN) for dry machining applications.

Cutting tool micro-geometry and surface integrity have been critical aspects to be considered for successful application of PVD thin films for cutting tool life enhancement. The present study examines in detail the role of pre-coating surface preparation (micro-blasting and drag finishing) on the tool life of coated cutting tools. TiN coating was deposited on different kinds of pre-treated (Micro blasting, Edge rounding and a combination of both) HSS and WC drills using cylindrical cathodic arc deposition method. They were subsequently characterized for surface roughness (Ra), adhesion strength and machining performance on EN 24 material. Pre-coating surface roughness (developed due to pretreatment) has a major influence on the adhesion strength of the coating. A lower pre-coating surface roughness with optimized edge rounding led to higher adhesion and edge strength which in turn resulted in a notable increase in tool life. Further underlining the importance of the present study, commercial TiN coatings deposited on HSS substrates were tested. The tool life obtained in the current study prolonged the tool life by a factor of 3 in comparison to the commercially available tools in the present day market.

CrAlSiN nanocomposite thin films with varying film chemistry were developed on tungsten carbide (WC) specimens using cylindrical cathodic arc physical vapor deposition (c-CAPVD) technique. The physical, mechanical, and tribological properties of all the films were comprehensively investigated for arriving at the film chemistry leading to the best properties with respect to mechanical applications. The best tribo-mechanical properties were obtained in films with Cr/(Al_Si) ratio of 1.2. This coating with best properties was translated on to WC drill bits for machining tests. The Al and Si content has shown major influence on the adhesion strength and phase constitution of the films, with a considerable change in residual stress too. The superior properties achieved could be attributed to the formation of a near-perfect nanocomposite structure, with the crystalline CrAlN phase surrounded by an amorphous Si3N4 phase. The tool life of the coated CrAlSiN tools was investigated during dry machining of EN 24 material. In comparison to the tool life of an uncoated tool and a TiAlSiN-coated tool, the best CrAlSiN coatings synthesized in this study performed exceedingly well. The present study clearly demonstrates the advantages of CrAlSiN over other existing similar coatings for high-speed machining.

Titanium chromium nitride (TiCrN) coatings with varying Cr content in two configurations, mono- and multilayer, were deposited on high speed steel substrates using a cylindrical cathodic arc physical vapor deposition technique. The physical, mechanical, and erosion behavior of the coatings were investigated. Among the monolayer coatings, the thicker Ti0.48Cr0.52N coatings yielded the best erosion resistance property. But with the increase in thickness, a considerable increase in residual stress is observed. Toward minimizing the stress accumulation, the effect of multilayering with periodic in situ heat treatment (after each 1 μm film growth) was studied by growing films in Ti0.52Cr0.48N/Ti0.40Cr0.60N bilayer configuration. A new approach based on % area of erosion damage for measuring relative wear rate of thin films has been proposed and implemented. The multilayer coatings exhibited superior erosion performance compared to the well-known erosion resistant TiN coatings that are in use for compressor blades from past few decades. Further, the erosion failure mechanisms in TiCrN coatings were also studied and found to be clearly different for mono- and multilayer configurations. The results reveal that the thicker multilayer TiCrN coatings (20 μm) exhibit promising choice for erosion resistance applications.

Chromium nitride (CrN) is well known as a hard protective coating by virtue of its high hardness and good corrosion and oxidation resistance. The addition of elements like Aluminium (Al) and Vanadium (V) to CrN results in enhanced high temperature stability and improved mechanical properties due to significant changes in microstructure, grain size and phase composition. In quaternary systems such as TiAlSiN and CrAlSiN, the presence of Silicon (Si) is reported to promote segregation of amorphous SixNy phase along the grain boundaries of nano phase materials. This particular microstructure has been shown to further enhance mechanical and high temperature properties. Since Titanium Aluminium Nitride (TiAlN) coatings have been well-studied, considerable work has also been reported on addition of Si to TiAlN and its resulting properties. However, the influence of addition of Si to CrAlN has not been fully studied, in spite of the promise of the resulting coating for many demanding biological (stunt over coat), solar (selective coat), mechanical (high speed dry machining) and tribological (erosion resistant) applications.