Erhard Broszeit

Development of chromium nitride coatings substituting titanium nitride

Abstract The deposition of chromium nitrides by reactive magnetron sputtering on machine parts seems to be very promising, because the mechanical properties are similar to those of TiN hard coatings. Especially the corrosion resistance of CrN is an interesting aspect related to the known problems of TiN films. The presented research deals with the deposition of Crue5f8N films by using r.f.-magnetron sputtering units. Starting with common deposition parameters for titanium nitride and a variation of the deposition parameters, partial pressure and bias voltage, chromium nitride coatings are deposited on steel substrates. The results show that the reactive sputtering process of Crue5f8N is more sensitive to minor changes of the adjustable deposition parameters and the related plasma conditions than that of TiN. The deposition of Crue5f8N allows the production of coatings with a wide field of properties but only within small windows of deposition parameters, especially when sputtering Cr2N films. The characterization of the coatings by their basic properties, such as thickness, hardness, adhesion, phase analysis and residual stress, indicates possibilities and limits of Crue5f8N coating systems.

The influence of a heat treatment on the microstructure and mechanical properties of sputtered coatings

The aim of this paper was to examine correlations between deposition parameters and the coating properties of RF-sputtered films in deposition conditions and after heat treatment at temperatures up to 700 °C. The investigations deal with titanium-, chromium- and hafnium-based nitrides, borides and ternary alloys. Different materials such as SAE 52100 steel, ASP 23 high-speed steel and Ti6A14V titanium alloy, which are commonly used in the aerospace industry, were coated to analyse the influence of the substrate material. The coatings were tested with respect to their phase composition, microstructure, residual stress, thickness, microhardness and adhesion. It is shown that the deposition parameters, as well as heat treatment at a temperature as low as 400 °C, can change considerably the coating properties.

Development of a plasma surface treatment for magnesium alloys to ensure sufficient wear and corrosion resistance

Extensive investigations of the authors showed the possibility of producing reliable plasma vapour deposition (PVD) hard coatings on magnesium alloys with good wear properties comparable to PVD coated steel or titanium based alloys. In presence of corrosive mediums crucial contact and pitting corrosion, induced by process related coating pinholes are the main failure mechanisms of coated magnesium alloys, even without any tribological load applied. The authors developed the new method of plasma anodisation to ensure acceptable corrosion resistance. In contrast to conventional anodisation processes the aqueous electrolyte is substituted by an oxygen plasma. The main advantages are that the process uses no toxic electrolytes, there is no waste and anodising and PVD-coating can be done in one process. The article gives a brief view of our extensive work starting from the first approach in PVD deposition of magnesium alloys up to the present work in establishing the plasma anodisation.

Plasma anodisation as an environmental harmless method for the corrosion protection of magnesium alloys

Sufficient corrosion resistance of technical magnesium alloys is generally ensured by anodising the components in aqueous electrolytes. In the majority of cases, these processes bear environmental risks due to the highly toxically electrolytes and are subjected to substantial legal regulations. Considering these facts, the plasma anodisation seems to be a prospective method to obtain comparable corrosion resistance without using toxic substances. The main goal of the method of the plasma anodisation is the substitution of the aqueous electrolyte by an oxygen plasma. The plasma anodised surfaces were well characterized and the corrosion resistance was proved in the salt spray test according to DIN 50021 SS. For the tests the magnesium die cast alloy AZ91hp was used. The tests included plasma anodised, plasma anodised and PVD coated and only PVD coated specimens.

Deposition, properties and applications of PVD CrxN coatings

Abstract The deposition, properties and application of PVD Cr x N coatings have been discussed increasingly in recent years. One reason for this are the environmental problems associated with the use of electroplated chromium and the resulting need for a replacement of the production method. Another reason for a discussion of PVD Cr x N is that the field of application of PVD TiN coatings seems to be examined up to the point were coating properties are difficult to improve by processing parameters. Cr x N is one answer to these two demands, showing similar mechanical properties to TiN and a good corrosion resistance. The following paper presents the engineering of functional properties of PVD Cr x N coatings performed at the Darmstadt University of Technology in the last decade. Boundary conditions of deposition by PVD r.f.-magnetron sputtering as well as characteristic physical and mechanical properites are presented, followed by selected tribological applications.

Adhesion and wear resistance of nitrided and TiN coated low alloy steels

Abstract Hardened and tempered low alloy steel grade 31CrMoV9 was gas and plasma nitrided to form a varied structure of the substrate for a subsequent TiN hardcoating. The process parameters of the nitriding were modified to form a sufficiently supporting diffusion layer with a thickness of more than 0.5 mm and a defined structure of the surface. Hardened cases without compound layer were formed using more step technologies in the nitriding process. The TiN coating was deposited by hollow cathode discharge evaporation. The composition and structure of the nitrided case, the mechanical pretreatment, the plasma assisted treatment directly before deposition as well as the deposition parameters influence the properties of the duplex treated steel. The adhesion can be improved essentially by an interlayer system Tiue5f8TiN x ue5f8TiN. Special consideration was given to the investigation of the adhesion and wear resistance of the composites. The wear tests include investigations of the sliding and abrasive wear. The results of testing rolling butt contact shows that a TiN layer on nitrided steel has no essential influence on the fatigue limit.

Effect of an annealing process on the tribological properties of sputtered hard coatings

Abstract This paper describes the influence of vacuum heat treatments up to 700xa0°C on the mechanical and tribological properties of sputtered PVD-coatings. We have deposited titanium, hafnium and chromium based nitride and boride layers on different substrate materials such as steel SAE 52100, ASP 23 high speed steel and titanium alloy Ti6A14V. It is shown, that hardness, adhesion as well as the brittleness of the coating varied strongly depending on the residual stresses of the film. The highest wear resistance could be achieved with hexagonal chromium nitride films. The annealing process could lead to a significant change of the wear properties, depending strongly on the layer composition. Titanium and chromium nitride coatings were hardly influenced by the heat treatment, whereas titanium and hafnium borides and ternary boron nitrides showed a remarkable increase of wear, when deposited with a thin titanium intermediate layer.

Properties of duplex treated (gas-nitriding and PVD-TiN, -Cr2N) low alloy steel

Abstract Gas-nitriding of low-alloy steel as a pretreatment for hard-coating deposition by hollow cathode discharge evaporation is well established. Above all, the produced nitrided case leads to a distinct increase in the resistance of the coating towards mechanical and chemical stress. Gas-nitrided samples of 31CrMoV9 coated with TiN and Cr 2 N were objects of extensive investigations to characterize their properties. The description of coating-substrate adhesion and the behaviour of the sample surface under tribological stress were the main subject of the experiments. The investigation of rolling wear with different geometries of contact and slips confirms the statement at the beginning. It was found that the bearable Hertzian contact stress is within the known range of bearing steels. The results are discussed from the viewpoint of stress field parameters (geometry of contact, slip) and case structure (for example, residual stress and the gradient of hardness).

Mechanical, thermal and tribological properties of electro- and chemodeposited composite coatings☆

Abstract By means of chemical (autocatalytic) and electrolytic codeposition of nickel and silicon carbide particles it is possible to produce coatings with enhanced wear and corrosion resistance on metallic and plastic substrates. In the first part of the paper the basic plating technique in relation to the type, form, grain size and activation of the SiC particles will be described. The mechanical properties of the coatings depend on the amount of incorporated particles in the nickel matrix. By activation of the SiC powder the content of particles in the coating can be increased significantly. Mechanical properties such as hardness, strength and elastic modulus improve with increasing content of particles. It will be further shown that the negative influence of a pure nickel coating on fatigue is reduced with a coating of Niue5f8SiC. This result can be explained by the behaviour of the internal stresses in the coating as a function of the SiC content. The tribological properties of the coatings were tested by an abrasive wear mechanism under lubricated conditions combined with corrosion. The corrosive wear tests were performed under potentiostatically controlled conditions. The high temperature application of these coatings is limited by the thermal decomposition of the SiC particles in the nickel matrix at about 500 °C. The coatings were examined by various techniques such as differential thermal analysis, X-ray diffraction and secondary ion mass spectrometry. The influence of different temperatures on the mechanical and tribological properties of the coatings will be described.

Tribological properties of sputtered CrN coatings under dry sliding oscillation motion at elevated temperatures

In the future dry running machine elements may play a more important role, due to environmental legislation. The economical demand for cost and timesaving causes higher mechanical and thermal stresses for tools in high-speed production processes. Is it possible to improve the wear resistance by the use of thin hard coatings and will they find an area of application especially at elevated temperatures where lubricants fail? Therefore, oscillating sliding motion dry wear experiments at specific temperatures ranging from 30 to 700°C (900°C is possible) were performed on PVD-coated steels and light metal alloys. The characterisation of the coatings includes fundamental properties such as thickness, hardness, structure and residual stresses. The tribological tests were done with an SRV3 apparatus from Optimol, the coatings were tested against 100Cr6 balls using a ball-on-disk arrangement. The friction and wear behaviour was documented. The wear traces were characterised using a Hommel Tester T 8000. Topographical microanalysis was done with SEM and EDX.