Cutting Tool Industry Research Articles

Effect of Surface Treatments on the Structural and Mechanical Properties of Nanostructured Diamond Coatings on Tungsten Carbide Cutting Tools

ABSTRACTChemical Vapor Deposition (CVD) using hydrogen, methane, and nitrogen feed gases has proven to be useful in depositing well-adhered diamond films on metal substrates. These films have already found a market in the cutting tool industry as coatings on cobalt-cemented tungsten carbide (WC-Co) inserts. The purpose of this investigation is to examine how the thermal and chemical pre-treatments typically used for carbide inserts (to remove the cobalt binder near the surface) affect the structure and interfacial adhesion of the diamond coating. Removal of the cobalt binder phase in various pre-treatment methods has been shown to minimize its catalytic effect of graphite formation during diamond deposition by CVD. The diamond-coated inserts in our study were characterized using x-ray diffraction, Raman spectroscopy, atomic force microscopy, and Rockwell indentation testing. We use an unconventionally high methane concentration in the feedgas in order to saturate the growth surface with carbon, thereby limiting cobalt migration from the bulk to the surface and reducing the dissolution and diffusion of carbon atoms coming from the plasma. Nitrogen is used in the feedgas in order to provide a tough, single-layer nanocrystalline diamond film structure. In addition, a multi-layer (nano-/micro-/nano-crystalline) CVD diamond film was grown by controlling the flow of nitrogen in order to show its characteristics in comparison with the single layer nanocrystalline diamond film. The multilayer film on the thermally-treated insert shows enhanced interfacial adhesion and fracture toughness when compared to other pretreatments and diamond coatings. This was demonstrated by indentation tests using 1470 N load.

Friction and wear testing of multilayer coatings on carbide substrates for dry machining applications

The principle aim of this paper is to investigate three wear-protective coatings with multilayer structures, which are frequently used in the cutting tool industry and to assess their frictional behaviour under the test conditions equivalent to those for the cutting of medium carbon steel. A modified pin-on-disc tester was used to conduct experiments in which both the friction coefficient and the linear wear of the tribo-pair were recorded vs. sliding distance. The volumetric wear rate was proposed as a parameter for quantitative comparison of the wear resistance of the tribo-pairs tested. It was found that the principle stage of the specimen wear takes place during the first 200–240 s of sliding independently of the applied speed; obviously, after this stage the intensity of wear decreases drastically. The maximum values of specific wear rate observed at the lowest sliding speeds applied decrease significantly with the elevation of the sliding speed for all tribo-pairs, especially for coated specimens. The use of coatings with an Al 2O 3 intermediate layer at the lower sliding speed of approximately 0.5 m/s deteriorates the wear resistance of the coated specimens, but its protective role becomes more important at the high speed conditions in comparison to an uncoated carbide specimen. The maximum wear resistance was revealed in the case of a carbon steel–TiC/TiN coating tribo-pair for sliding speeds ranging from 0.5 to 3.0 m/min. It is concluded that the proposed methodology for experimental friction and wear quantification provides the new knowledge for multilayer coating structures on the cutting tool wear resistance and can be helpful in the optimum selection of coated tools for the dry cutting of steels.

Recycling of WC–Co from scrap materials

WC-Co scrap generated by the cutting tool industries was electrochemically broken down to cobalt, which was deposited at the cathode and a mixture of tungsten oxide and tungstic acid was collected at the anode with an overall recovery efficiency of about 90%. The tungsten oxide/tungstic acid was reduced to produce nanostructural tungsten powders, which were subsequently carburised and chemically coated with cobalt to produce WC-Co powders. The powders synthesised were characterised for purity and size.The WC-Co powders, thus obtained were consolidated to near theoretical densities using a novel plasma pressure compaction (P2C) technique. The microhardness of the consolidated sample was measured to be 2200 HV, which is 20% higher than the reported literature values.

Challenges facing surface engineering technologies in the cutting tool industry

At the advent of the new millennium cutting tool manufacturers are finding themselves supplying tools to a market that demands ever increased performance and reliability. Technological advances in machine tool design, tool control and monitoring systems have helped facilitate the development of high-speed machining, near net machining of difficult to cut materials and dry cutting methods. Parallel advances in cutting tool technology have aided these developments with the application of surface engineering technologies being of prime importance. The current paper considers the shift in workpiece material type used in manufacturing and the subsequent change in the cutting tool materials used to machine them. To take full advantage of the potential benefits of advanced surface engineering treatments the need to address the requirements of a cutting tool in terms of geometry, substrate material, edge preparation and surface treatment are described with reference to TiN coating of high-speed steel circular saw blades. Current trends in cutting tool technology are then considered together with the benefits and practicalities of applying advanced surface engineering coatings.

Some effects of ion beam treatments on titanium nitride coatings of commercial quality

Abstract The present work deals with effects of N + ion implantation on the structure and properties of TiN coatings used in the cutting tools industry: The characterization was performed using glancing incidence X-ray diffraction (GIXRD) and depth-sensing microindentation (ultra-microhardness). Results from PVD-type films are compared with those obtained from CVD TiN. Amorphization was noticed in the former, but not in the latter. Large changes in the residual stress and strain distributions are observed in the implanted zone and hardness measurements show a decrease in hardness after implantation with nitrogen in both PVD and CVD films. The correlation between the tribological data, nanohardness and the observed structural changes is presented and discussed.

Technology transfer issues for hard coatings in the cutting tool industry

Many issues must be successfully addressed to scale up and transfer new coating technology into manufacturing. Connections between R&D and manufacturing groups must be synchronous on technical, informational and organizational levels. Parallel equipment and processing capability in both groups is important for smooth technology transfer. Also, flexibility must be balanced with automation for rapid product development and transfer. Modeling of several types (thermodynamic, FEA-based solid and flow/heat transfer) is becoming a key tool to save time and resources during development. Several examples are given for flow and heat transfer modeling in a CVD system. Despite advances in technology, the human element is still the most critical in effectively developing, scaling-up and transferring new technology.

Ultrashort pulsed laser ablation of diamond

Laser processing of diamond and chemical-vapor-deposited diamond thin films are important in the microelectronics and cutting tool industries because the manufacture of diamond films with low surface roughness and complex shapes has proven to be difficult. In this paper we present a review of current laser polishing and ablation processes followed by a discussion of ultrashort pulsed processing of diamond. Compared with the use of longer pulsed lasers, the use of 248-nm, 500-fs duration pulses at extreme intensity offered multiple advantages, including a lack of lateral thermal damage and significant improvements in the structural purity of the ablated surface. Experimental data, including Raman spectra and scanning electron micrographs, were presented to demonstrate the superior capabilities of this new class of lasers for diamond processing.

Use of Chromium Carbide in Thermal Spray and Other Coating Technologies

London and Scandinavian Metallurgical Co. has been a supplier of specialist raw materials to the metallurgical industry since 1938. These raw materials are constantly being developed and finding new applications. One of them is a chromium carbide which was originally developed for use in the cutting tool industry and as a weld overlay and is now finding application as a constituent of thermal spray powders, where it is used as an environmentally friendly alternative to hard chrome coatings delivering wear and corrosion resistance.

Preparation of Ti(C,N)-WC-TaC solid solution by mechanical alloying technique

Mechanical alloying (MA) is a dry, high energy ball milling process for producing composite metallic powders with a fine controlled microstructure. Traditionally, the raw materials used in MA must include at least one fairly ductile metal to act as a host or binder to hold together the other ingredients. MA is believed to occur by repeated welding and fracturing of a mixture of metallic and nonmetallic powders in a highly activated ball charge. Reported here, however, is a study of the mechanical alloying process of all ceramic phases, i.e., Ti(C0.3N0.7) + WC + TaC. The three ceramic powders were mixed in weight proportion of 70:20:10 and milled in a planetary ball mill at a ball-to-powder weight ratio of 20:1. X-Ray diffraction examinations were performed after MA for different time. It was found that TaC peaks progressively reduced in intensity with milling time and disappeared after 88 hours. Though there was an over-all peak intensity drop for every species, WC peaks persisted and remained well defined. The half-peak-width of the powders increased significantly after MA indicating decrease in the coherent crystalline domain size. Pycnometry density measurements of the mechanically alloyed powders indicated that the density of the powder mixture decreased with milling time. Energy Dispersive X-Ray (EDX) studies showed that Ti, W, Ta all exist in the same particle after 131 hours of milling, indicating progress of the solid solution process. Hard phase solid solution of carbonitride of Ti, Ta, W is a source powder in making high toughness carbonitride cermet cutting tools. Success in producing this hard phase solid solution by Mechanical Alloying opens up a whole new avenue in cermet cutting tool industry.

Metal-carbon layers for industrial application in the automotive industry

Physical vapour deposition (PVD) coatings have been well established in the cutting tool industry for many years. In the near future the high wear resistance and low friction coefficient of PVD coatings will be of interest for applications in constructional elements. Today the deposition process and the quality control of coated parts are accompanied by several problems: during the deposition process the temperature of the constructional elements must not exceed 200 °C; the composition of the deposited layers has to be reproducible; methods for the quality control of coated parts need to be integrated in series control. These problems will be discussed for reactively sputtered metal-carbon layers (W-C:H). Methods of quality control such as Rockwell C indentation and glow discharge optical spectrometry will be illustrated. First applications of W-C layers in the automotive industry are presented.

Microstructure and hardness of Ti(C, N) coatings on steel prepared by the activated reactive evaporation technique

In view of the potential demand for wear-resistant coatings deposited at low substrate temperatures for applications in the cutting tool industry, titanium carbonitride films were prepared by the activated reactive evaporation technique on high speed steel substrates. Titanium was evaporated in C 2H 2N 2 plasmas of various compositions ranging from pure C 2H 2 to pure N 2, i.e. in C 2H 2 with 0, 30, 50, 70 and 100 vol.% N 2. Knoop hardness values (at 50 gf load) were obtained both on top and in the cross section of each deposit and ranged from 2200 to about 5900, reflecting the variations in chemical composition and microstructure of the films. X-ray diffraction, transmission electron microscopy and scanning transmission electron microscopy analyses were performed to reveal those microstructural features of importance to the coating properties, i.e. phase composition, grain morphology and defect distribution (in particular, void and crack formations).