ICMCTF2003 Session G1/TS1: Innovations in Surface Coatings and Treatments

New hybrid plasma sources for both low gas pressure processing (<10^-2 mbar) and for generation of cold atmospheric plasma were designed, developed and tested, [1,2]. The sources combine advantages of the microwave plasma with the hollow cathode plasma in a common system. The low-pressure hybrid plasma source (HYP LP) combines the ECR (Electron Cyclotron Resonance) plasma inside microwave radiator and the radio frequency (RF) hollow cathode plasma generated by linear magnetized hollow cathode at the outlet of the radiator. The plasmas are coupled together in a common magnetic field facilitating both the hollow cathode plasma and the ECR absorption of the microwave power in the vicinity of the cathode outlet. The plasma density measured 15 cm below the source outlet at 1 kW incident power from both generators reaches 5 x 10¹¹ cm^-3 at argon pressures of the order of 10^-3 mbar. This classifies the HYP LP source as a high-density plasma source. The plasma density in the reactor chamber is very uniform which is important for large-area processing applications. The TiN film deposition rate of about 150 nm/min was achieved in the reactive PVD of highly (111) textured TiN films at gas pressure of 7 x 10^-3 mbar. Operation principles of the HYP LP sources open an exciting opportunity for future developments of non-conventional composite coatings and for coating property engineering. The atmospheric pressure hybrid plasma source (HYP AP) combines a microwave antenna and a RF hollow cathode in a common electrode. The source is able to produce atmospheric plasma plumes and to control plasma parameters efficiently. The HYP sources have a full ambition to become new processing tools on the market, suitable either for new systems or for upgrade of existing systems.

[1] L. Bardos and H. Barankova, Swedish patent 9904295-4, PCT/SE00/02315.

[2] EU Project "HYBRID", Nr. GRDI-1999-10393.

The film deposition conditions on individual specimens located in various positions in the vacuum chamber during a PVD coating procedure, with constant power law, can not be considered as identical. Depending on the applied deposition parameters, such as the magnetic field distribution in the vacuum chamber, the specimen fixture geometry and its kinematics etc, the occurring coating crystalline structure and thus the hardness and the mechanical properties might vary.

In order to investigate the effect of coating hardness and strength properties deviations on the cutting performance, occurring due to the aforementioned peculiarities during a PVD process, (Ti₄₆Al₅₄)N films with thicknesses from 2 up to 10 µm were deposited on cemented carbide inserts in individual PVD processes. The obtained coating material properties and especially their stress strain laws, were determined by means of a FEM-based evaluation procedure of nanohardness measurement results. Moreover milling experiments to investigate the effect of the mechanical properties variations on the cutting performance in the examined coating thickness cases were conducted. The initiation and progress of the tool failure was depicted through Scanning Electron Microscopy (SEM) observations and Energy Dispersive X-ray microspectral analyses of the used cutting edges.

The investigations showed that an increasing of the coating thickness diminishes the superficial coating strength, however leads to a cutting performance enhancement. The numerically extracted results based on a FEM simulation of the milling process, explain the achieved cutting performances at various coating hardnesses and thicknesses.

Furthermore the obtained results illustrate that the coated tool cutting performance is less affected by potential coating mechanical properties deviations in the case of thick coatings, in comparison to thinner ones, where corresponding differences in coating mechanical properties significantly deteriorate the cutting performance.

Most commercial ion sources available today provide for a continuous or steady flux of ion beam current. For stable operation, these sources generally require a static, stable and, in some cases, controlled vacuum environment. In a real vacuum deposition system, this is not always possible to achieve and can result in unstable behaviour. This problem is usually related to changes occurring in the load (the ion source) that is presented to the power supply.

At Saintech we have been exploring ways to reduce this problem by, effectively, de-coupling the power supply from the ion beam system. There are several ways of achieving this and we have been exploring two such techniques. So far we have been successful in operating the ion source in a pulsed mode where the pulsing is achieved by electronically opening and closing a valve to admit small quantities of process gas. The pulse frequency and duration are independently controllable. Feeding the gas pulses from a constant pressure manifold controls the energy in the pulses. The pulse energy can be as high as several amps at ion energies of 200 eV. The duty cycle can be as much as 10:1 (ON pulse 1000 msec : OFF 100 msec) to 1:250 (ON 100 msec : one pulse every 25 seconds). The former parameters have application to IAD of most metal oxide materials while the latter parameters have application to the IAD of many IR and UV film depositions.

There are many advantages resulting from this mode of operation: 1)Highly stable and reliable operation. 2) Lower average gas flow without sacrificing average energy. 3) Extended filament life. 4) More compatible with the operation of thermal and electron beam evaporators. 5) Easily interfaced with process controllers. 6) The IAD of many film stacks can be carried out at very low pressures because the average gas flow can be as low as 1 sccm of process gas.

New and modern coating technologies have great potential to improve and, or enhance the life of cutting tools. The surface conditions or characteristics of the tool surface and cutting edge to provide better wear resistance and hence improvement in tool life, is governed by having a good knowledge of the tool geometry, especially the condition of the cutting edges and of the surface characteristics. The performance and failure modes in multi-point cutting tools such as circular saws and band saws are more complex than those in single point tools. Consequently the coating possibilities, requirements and limitations for multi-point tools are different to single point tools.

The paper characterises the cutting tool geometry and the surface properties of industrial saws. Surface requirements and tool preparations, which are necessary for wear resistant coatings, are described. Suitable advanced coating processes are shown and the performance of the coated tools determined through cutting tests and metallographic analysis are presented.

The paper should be of interest to the materials engineer, surface coater, cutting tool designer and manufacturer.