Jan Walkowicz

Influence of the structure of the composite: 'nitrided layer/PVD coating' on the durability of tools for hot working

Abstract The paper presents research results of the influence of the ‘nitrided layer/PVD coating’ composite on the durability of tools for hot plastic working. Four structures of the composite differing in the PVD coating material were investigated. They were: TiN, CrN, (Ti,Cr)N and Ti(C,N). The composites investigated were created by means of the surface ‘duplex’ treatment method in a two stage separable cycle (the nitriding process and the PVD coating deposition were carried out with different devices). The nitriding process was executed with the use of the regulated gas nitriding method, whereas the PVD coating was executed by means of the arc-vacuum method. The tools tested were forge dies made of ISO steel 35CrMoV5 (0.4%C, 0.4%Mn, 1.0%Si, 5.0%Cr, 1.3%Mo, 0.3%V) designed for the plastic working of automotive half-shafts. The paper presents the results of maintenance investigations, executed under manufacturing conditions, obtained for tools used for hot forging which were covered with different composites. The investigations proved that the best durability was achieved for tools covered with the composite ‘nitrided layer/CrN coating’, for which the increase in durability was almost 90%. The smallest durability was noted for tools covered with the composite ‘nitrided layer/TiN coating’. The results obtained proved that a proper choice of the composite ‘nitrided layer/PVD coating’ structure may increase the durability of tools considerably for hot plastic working.

Duplex surface treatment of moulds for pressure casting of aluminium

The subject of this paper is the technology of the production of composite-nitrided case/TiN coatings. This technology is used for improving the lifetime of tools operating at heavy thermal and mechanical loads and at conditions of intensive abrasive wear. In the case of such tools, the standard methods of improving the surface properties by thermal treatment, thermo-chemical treatment or by deposition of anti-wear monolayers [e.g. TiN, Ti(C, N)] do not lead to the desired increase in tool life. This goal can be achieved only by the application of a duplex surface treatment which involves beside the deposition of mono and multilayers, a thermo-chemical treatment (for example, nitriding), and determining the structure and properties of the tools surface layer. As a result of a duplex treatment, a multi-layer composite is obtained, which in terms of anti-wear properties outdoes both diffusion layers obtained by thermo-chemical treatment and multilayers deposited by PAPVD methods. The chemical composition and internal structure of the composite must be selected with regard to its final application. The technology of duplex surface treatment was used to improve the durability of moulds for aluminium injection moulding.

Optimization of nitrided case structure in composite layers created by duplex treatment on the basis of PVD coating adhesion measurement

Abstract The paper concerns the process of the composite: ‘nitrided layer-PAPVD coating’ creation on substrates made of hot working steel. The composite properties are determined by the appropriate selection of coating parameters and nitrided case structure. The results of research concerning the influence of a method of substrate nitriding and the created nitrided case structure on the adhesion and plastic properties of the PAPVD coatings are presented in the paper. Substrates made of hot working steel EN X35CrMoV5 (0.4% C, 0.4% Mn, 1.0% Si, 5.0% Cr, 1.3% Mo, 0.3% V) underwent different processes of thermo-chemical and finishing surface treatment in order to obtain a nitrided layer of a different structure: Fe α (N), Fe α (N)+‘white layer’-E,γ′. Research was carried out for nitrided layers created in a controlled gas nitriding process. Four different coatings of nitrides, TiN, Ti(C,N), CrN, (Ti,Cr)N, were deposited on substrates with nitrided layers using the arc-vacuum method and the MZ-383 equipment manufactured by Metaplas Ionon. For composite nitrided layer/PAPVD coating’ prepared in this way, the authors carried out a metallographic analysis, using the optical microscope Neophot32, and measurements of surface roughness of the deposited nitrides. The X-ray phase analysis carried out on the Philips PW1830 diffractometer enabled the phase composition of nitrided layers and the phase composition and the lattice parameter of the deposited PAPVD coatings to be determined. Then, the authors carried out measurements of the coating adhesion for all investigated composites using the scratch-test method by means of Revetest-CSEM. The authors demonstrated the significant influence of the presence of titanium ions (Ti + ), in the vacuum arc deposition process, on the properties of the composite nitrided layer/PVD coating. The presence of titanium ions in the technological process deteriorates adhesion of the PVD coating to the nitrided substrate, when the nitrided layer includes the compound zone. This effect was not observed for a CrN coating deposited without the participation of titanium ions.

On the mechanisms of diode plasma nitriding in N2–H2 mixtures under DC-pulsed substrate biasing

Abstract The results obtained by the author proved that in the conditions of investigated processes the nitriding intensity was influenced by three components of the gas–plasma atmosphere: nitrogen and hydrogen (supplied as the working gas mixture) as well as argon (used as a component of the atmosphere at the stage of initial heating of the substrates before nitriding). The revealed correlation between composition of supplied N 2 –H 2 mixture and: nitrided layer structures, plasma resistance, degree of molecular nitrogen dissociation and concentration of nitrogen molecular ions N 2 + shows that both ionized and neutral nitrogen particles participate directly in the nitriding process. The content of N 2 , H 2 and Ar in the nitriding atmosphere determine characteristics of the discharge and relative concentration of nitrogen active species, thus nitriding ability of the individual nitriding processes. On the basis of obtained results, the author proposed the model of mechanisms of diode plasma nitriding taking into consideration intensity of different mechanisms at different nitriding temperatures.

Anti-wear properties of Ti(C,N) layers deposited by the vacuum arc method

This article presents results of investigations of multi-component coatings of the Ti(C,N) type used to improve durability of cutting tools. The coatings were deposited on tools made of high-speed steel and sintered carbides by the vacuum arc method. The working atmosphere was composed of nitrogen and acetylene. Wear tests were carried out in laboratories and on industrial scale.

Design and performance of the microdroplet filtering system used in cathodic arc coating deposition

The paper presents construction of a very simple and effective microdroplet filtering system. It describes the spatial angular distribution of different fractions of microdroplets generated by the cathode spots of the vacuum-arc evaporator equipped with the microdroplet filter and without it. The system was applied for TiN coating deposition. The influence of the filtering system on the TiN deposition process parameters is shown. Some properties of the TiN coatings (morphology, roughness, hardness and Youngs modulus of elasticity, chemical composition and their adhesion to the steel substrate), deposited with the use of this filtering system, are pointed out.

Investigation of the influence of ion etching parameters on the structure of nitrided case in hot working steel

Abstract The paper discusses the influence of the ion etching process on the nitrided case structure created with the use of the gas nitriding method in hot working steel. The nitrided case structure is of key importance for the final effect of duplex treatment, consisting of the nitriding process and subsequent deposition of a hard coating, because it significantly determines the adhesion of PVD coating. It was found out that during the initial stage of the coating deposition, i.e. during ion etching, decomposition of the E and E+γ′- ‘white’ compound layer can occur, which results in backward diffusion of nitrogen and destruction of the created nitrided case. The critical temperature for the decomposition process is 500°C, although in some conditions, it can start even at 350°C. The purpose of the investigation described in the paper was to examine changes in the nitrided case structure (in the hot working steel ISO 35CrMoV5) caused by the etching process executed in different experimental conditions (1: different pressures: 2×10 −5 mbar, 1×10 −3 mbar, 1×10 −2 mbar; 2: different working atmospheres: titanium plasma and mixed titanium–argon plasma; 3: two types of substrate polarization: U bias =900 V/d.c., and pulsed U bias =900 V, f =5 kHz, Δ=90%. The experiments were carried out in the vacuum arc deposition equipment MZ383 manufactured by Metaplas Ionon (Germany). Prepared samples were examined, before and after ion etching, in the microscopic metallographic investigation using the optical microscope Neophot32 and in the investigation of the phase composition using the X-ray diffractometer Philips PW1830. The influence of the ion etching process conditions on the nitrided layers structure and on the intensity of compound zone decomposition was characterized on the basis of results obtained from experimental investigations.

Spectral characteristics of vacuum arc discharges with Ti and Zr cathodes

Abstract Spectroscopic study of two types of arc sources, used for industrial deposition of hard coating has been performed. The arcs with titanium and zirconium cathodes worked in vacuum, N 2 or N 2 +C 2 H 2 atmospheres. Atomic and molecular spectra excited in the arc discharges have been identified. Relations between spectral intensities of neutral (Ti I, Ar I, H, N 2 , CH) and ionised (Ti II, Ti III, Zr II, Zr III, Zr IV) species and current have been investigated at various experimental conditions. Spectroscopic characteristics of the discharges and mechanism of excitation have been discussed.

Research on physico-chemical bases of the ion nitriding process control with the use of plasma spectroscopic diagnostics

Abstract The results of the research which concerns assigning correlation between parameters of the glow discharge plasma, observed by spectroscopic methods, and kinetics of the nitriding process and the nitrided layer structure are presented in the paper. Research on the plasma parameters was carried out for two processes of the ion nitriding enabling creation of two basic structures of the nitrided layer: containing exclusively the diffusion zone α -Fe(N) and containing both, the diffusion zone α -Fe(N) and the compounds zone e + γ ′. Mass spectra of the gas atmosphere and emission spectra of plasma generated in the near-surface area were recorded at the succeeding stages of processes creating both the above mentioned nitrided layers structures. On the basis of the obtained results active plasma components, decisive for formation of individual structures of the nitrided layer, were assigned.

Optical emission diagnostics of the linear magnetron sputtering discharge

Abstract Spectroscopic study of properties of plasma produced in a new type of d.c. planar magnetron sputtering system—linear magnetron, with a titanium cathode and argon–nitrogen mixtures are presented here. High energy species (Ti, Ar, Ar + , N 2 , N 2 + , TiN) have been identified in plasma. Optical emission spectroscopy data were obtained showing the effects of operating parameters (pressure, current, argon percentage in Ar–N 2 gas mixture, axial position) on emission intensities of the species. In particular, the discharge current dependence of the emission intensities have been determined. Electron excitation temperatures were calculated from argon and titanium atomic lines. The results were used to characterize the excitation and ionization processes as well as sputtering conditions in the linear magnetron sputtering device.