C. Barimani

Comparison of the structure of PVD-thin films deposited with different deposition energies

Abstract Under the various available PVD processes, thin films can be deposited with higher or lower deposition energy, e.g., with or without ion bombardment. Related to this deposition energy the structure and consequently the properties of the deposited films can be directly influenced. The wide range of possible deposition parameters for the PVD-processes enables the use of materials in form of thin films in a large scope of applications, as a result of the different properties which can be achieved. Particularly high adhesion of thin films is always desired, which depends among other things on the microstructure of coatings. The aim of this paper is to compare three different PVD deposition processes: cathodic arc evaporation, magnetron sputtering and electron beam evaporation. These PVD processes are related to their film structure produced under three different conditions and studied interms of their deposition energies. Structure and morphology of the coatings are compared at identical temperatures resulting in a model, which is suggested to explain how excitation of deposited films takes place. Besides condensation effects, the momentum transfer of ions caused by biasing the substrates is obviously important and leads to film densification without increasing the substrate temperature.

Investigations on hard coated reamers in different lubricant free cutting operations

Abstract The reaming finishing process sets special high demands on quality and wear resistance of used reamers. Only the best adapted cutting geometries and parametric cuts allow to obtain high surface qualities and minimum deviations from circular form. Cutting operations carried out free of cooling lubricant will cause an extreme increase in thermic and abrasive load of tools. Details given in this paper will show how, using PVD coatings, it nevertheless is possible to obtain relevant file-proven tool life results, and certainty of operation in lubricant-free reaming and lubricant-weak reaming of gray cast iron (GG25) and aluminium alloy (AlSi12). Various arc-coatings and coatings deposited by sputtering are analyzed as to their mechanical properties, and wear behaviour is compared in application. In dry reaming of gray cast iron, good tool life could be obtained, even for a high cutting speed of 100m min−1, with modified coating materials (TiAlN, TiAlCN, for instance). These are compared with other coating materials (for instance TiZrN). Cutting of AlSil2 was done successfully with TiAlN-and TiB2-coated reamers.

Deposition of arc TiAlN coatings with pulsed bias

Abstract It is a well-known fact that the aluminium content of TiAlN coatings deposited with the arc physical vapour deposition (PVD) process depends mainly on substrate potential and source-to-substrate distance. To achieve good results in cutting operations with TiAlN-coated tools with a low aluminium content in the film, it is necessary to deposit TiAlN with a relatively high bias voltage which raises the substrate temperature to a level which can cause some damage to the structure of even high speed steel substrates. For high performance cutting operations with TiAlN thin films a high and homogeneous aluminium content in the films, especially on cutting edges, is necessary. Higher aluminium content in arc PVD thin films is achieved with lower bias voltage during deposition which in turn lowers the deposition temperature and consequently enables heat-sensitive substrates to be coated; however, for good adhesion of the deposited films a high bias voltage is required. The application of a pulse bias generator instead of a d.c. bias offers the possibility to decrease the deposition temperature and to obtain more aluminium in the coating. In this paper we compare coating properties of TiAlN deposited with d.c. and pulsed bias source. With pulsed bias it is possible to achieve higher aluminium content in the coating, especially on cutting edges. Analysis of increase in aluminium on cutting edges was carried out by energy-dispersive X-ray analysis.

The multisource arc process for depositing ternary Cr- and Ti-based coatings

Abstract The physical vapour deposition arc process offers the possibility to deposit many different coating systems. Usually the single-source mode is applied for the deposition of ternary hard coatings using alloyed cathodes. For the deposition of efficient coatings, suitable cathode materials for the arc evaporation have to be developed. Being often very costly, this development can be avoided through the use of the multisource mode (MSM), where each element is assigned to a separate evaporator unit. Coatings within the systems Ti-Al-N, Ti-Cr-N and Cr-Al-N are deposited by applying the MSM. In addition to the fact that a deposition of coatings within the system Cr-Al-N can be realized only with MSM, the results show that MSM coatings have at least equivalent quality when compared with coatings produced in the single-source mode. The MSM coating process may be characterized by the superposition of the evaporation behaviour of the single elements. Potential process variations and their influence upon coating properties are illustrated within the Cr-Al-N system.

Cr-C-N coatings deposited with different reactive carbon carrier gases in the arc PVD process

In recent years, significant improvements in the performance and quality of many machining processes have been achieved through the deposition of PVD hard coatings on the applied tools. Depending on the machined material process, e.g. turning, milling or drilling, not only different machining parameters but also different coating materials are necessary. In interrupted cut machining of tempered steel, for example, the lifetime of Ti-C-N-coated inserts is several times greater than that of TiN-coated ones. This is a result of the favourable thermophysical and tribological properties of Ti-C-N. The potential for tool protection by CrN coatings is a result of the high ductility and low internal stresses of this coating material. CrN films can be deposited with greater film thicknesses, still maintaining very good adhesion. This paper presents the development of new arc PVD coatings in the system Cr-C-N. Owing to the carbon content in the coating, an increased hardness and a better wear behaviour in comparison to CrN was expected. The effects of various carbon carrier gases on the coating properties were examined. The coating properties were investigated by mechanical tests, X-ray diffraction and SEM analysis. Some of the coatings were tested in machining tests. The results of these tests are presented.

PVD coatings on aluminium substrates

Abstract It is well known that aluminium is today the most widely used metallic material besides steel. The mechanical characteristics of aluminium offer an increasing application field, especially where lightweight constructions are required. The demands for improved characteristics such as higher strength and greater durability are achieved by the development of new aluminium alloys. Continuous efforts are made in research into new possibilities for making use of the advantages of aluminium in applications that were reserved up to now for harder and more wear-resistant materials. Because of their environmental benefits modern PVD processes represent a better alternative to a number of conventional coating processes to deposit wear-resistant films on aluminium surfaces. The aim of this paper is to describe the possibilities of TiN coating on an aluminium alloy, AlMgSi1, by application of the arc-PVD process without damage to the heat-sensitive substrate material. Different machining and cleaning processes were used for the preparation of the aluminium substrates. The relationship between substrate pretreatment and coating characteristics is demonstrated. The influence of different process parameters such as etching, bias voltage and coating time as well as the arrangement of the substrates in the vacuum chamber were investigated. Multilayer (Ti and TiN) and graded coatings were deposited on the aluminium alloy to achieve the best results in deposition rate, microhardness and critical scratch load. To characterize the abrasive wear behaviour of the coated aluminium substrates a special sandblasting test was used. These results are also described in this paper. Finally a suitable process technology is provided for the application of thin protective films on aluminium in order to increase wear resistance.

Arc evaporation of multicomponent MCrAlY cathodes

Abstract A major aim in todays development of aircraft and land-based gas turbines is the higher efficiency of the combustion process. The base material of the components is optimized for its mechanical properties, such as its creep strength or low and high cycle fatigue behaviour. Therefore, the corrosion and oxidation resistances have to be improved by an overlay coating. In fact, most Ni-based turbine blades are protected by an MCrAIY overlay. The conventional deposition method for this coating is low pressure plasma spraying (LPPS). As a result of new demand on the quality of hot gas corrosion-resistant MCrAIY coatings, processes that are alternatives to LPPS are under investigation. Evaporation with a cathodic arc is one possibility with technical and economical potential. Arc PVD systems are in use for several applications. Most actual target materials are only made of one or two elements. Therefore, the study of the behaviour of the arc, running on multicomponent target materials, such as the MCrAlY compositions with 5–7 elements used, is very important. The paper reports on the basic deposition phenomenas of the cathodic arc and presents the coating compositions and structures in the “as-depo sited” and homogenized states. It is shown that the chemical coating composition is different from that of the cathode material, but the difference is relatively small, so that the composition desired in the coating can be reached by proper adjustment of the cathode material. The morphology of the MCrAlY coating shows the two- or three-phase structure which is typical for this type of hot gas corrosion-resistant overlay. A sufficient bond strength of the coating was measured, so that the industrial application of this coating is possible. The proces itself offers new possibilities, such as the deposition of multilayer structures and the combination of the MXrAlY with a high temperature diffusion barrier, so that new improvements of the coating system can be achieved in one step. Summarizing the evaluation of the results shows that the arc technology is competitive with the conventional deposition techniques and offers some new possibilities for improved complex coating systems.

PVD coatings for lubricant-free tribological applications

This paper outlines the potential of hard coatings for ball bearings to achieve lubricant-free employment. The examined bearing type is an axial ball bearing (type no. 51107). This bearing combines a rolling and a sliding movement of the balls that induces a dynamically normal and shear stress into the coating. The rings consist of 100Cr6, a typical bearing steel. The ball consists of Si3N4 bulk material. A special test bench was developed to examine the coated axial ball bearings. This test bench permits the investigation of very different test conditions by varying several parameters, such as axial force and speed of rotation. The coatings were deposited using the magnetron sputter ion plating technique. At the first stage the coating material systems were developed and adapted to the substrate material and its heat treatment. The optimised process was than used for coating the bearing rings. The reduction of the substrate temperature below its tempering temperature of 180 °C during the coating was a very important aspect. Therefore the rings could be coated without having their hardness reduced. After the preliminary experiments the coated rings were tested in the test bench and compared with an uncoated ball bearing. During the test no lubricant was used.

Arc PVD-coated cutting tools for modern machining applications

Present research work in machining determined by ecological and economical reasons is focused on working without cooling and lubrication, high speed cutting (HSC), near net shape production and rapid prototyping. To achieve the desired aims in productivity and quality, modern high-performance machining tools as well as the adapted tooling machines and process parameters are necessary. In particular, the machining of tempered or austenitic steels requires complex mechanical, thermal and tribological properties from the applied tools. Since conventional high-speed steel or cemented carbide tools often cannot fulfil these high demands, new efficient cutting tools have to be developed. This paper presents the development of new arc PVD coatings in the systems Ti-Hf-C-N. The coatings were characterized due to the desired property profile for special cutting operations. For the machining of austenitic steels, coatings with a low friction coefficient to austenite and a high adhesion to the substrate are necessary. These properties were investigated by pin-on-disc and scratch tests. The thermophysical properties and thermal stability of the coatings, which play and important role in dry machining, were determined by photothermal spectroscopy, ice-tribometer tests and high-temperature X-ray diffraction. The results of the machining tests of the new coatings deposited on cermets are presented in another paper.

Simulation of the deposition process in PVD-technology

Abstract The PVD-technology and here the magnetron sputter ion plating technology (MSIP) has been applied in various modern technological fields owing to the wide range of possible coating materials. Besides electronic, optical and decorative applications, hard and protective PVD-films, in particular, have been widely applied as coatings which play an important role for the resistance against wear and corrosion. Such coatings have already been developed or are in industrial use. Although individual effects and phenomena that are brought along with the development of the PVD process, have been known for a long time, the theoretical description of this process is not completely matured. Up to now the development of thin films and the optimization of process parameters is still depending mainly on empiricism and experiments. In the MSIP process many random interactions of particles occur simultaneously. Therefore it is impossible or difficult to describe the process by some simple formulas. But with the tool of computer simulations it is possible to investigate the relations between the properties of the film and the process parameters. The present paper describes the activities of the Materials Science Institute on computer simulation of the PVD MSIP process.