Model Wear Tests Research Articles

Carbonitriding of Forging Dies

Forging dies have to resist high mechanical and thermal loads. Therefore, they are usually nitrided. Former investigations showed that the abrasive wear at the critical parts of the dies is much higher than the nitriding hardness depth. Carbonitriding offers the possibility to increase the hardness depth in shorter treatment times because of the higher treatment temperature. The (carbo-)nitrided surface region obtains a better hardness at elevated temperatures and a better wear resistance than the untreated steel. In order to create a wear- and corrosion-resistant compound layer at the surface, a nitriding process step can be conducted after carbonitriding. The present work deals with developing a carbonitriding treatment for forging dies and investigations on the wear resistance of the created surface zones in model wear tests and tool life time experiments under industrial conditions. The aim of this work was to produce heat- and wear-resistant precipitation layers in hot working tool steels in economical treatment durations.

Tribological Stress Behaviour of Cast Iron without and with Surface Treatment under Concentrated Contact Load*

AbstractThe graphite inclusions typical of grey solidified cast iron materials reduce the load-bearing capacity under locally concentrated pressure and simultaneous sliding stress. Surface treatment processes such as nitriding and electron beam remelting are known to improve the local stress behaviour. In this paper, the effects of the above-mentioned individual processes and their combination on the tribological stress behaviour of ferritic and pearlitic cast irons with different graphite morphologies are discussed. The results obtained in the model wear test ball-plate show that the specific wear coefficient of the investigated cast irons with different graphite morphology can already be reduced by at least one order of magnitude by an approx. 0.5–0.9 mm thick remelted surface layer with a surface hardness of 650–750 HV1. This treatment eliminates the graphite and produces ledeburitic carbides instead. The potential of an additional nitriding treatment depends on the parameters used, i. e. the nitrided layer thickness produced as well as the phase composition and the pore fraction of the compound layer. Based on stress calculations, the experimentally determined main influences such as the coefficient of friction, the pore fraction in the compound layer and the magnitude of the Hertzian pressure on the contact stress could essentially be confirmed.

Selection of diamond coated silicon nitrides for use as ceramic end mills when machining glass and carbon fiber reinforced plastics

The machining of advanced materials is challenging the tooling technology. To cope this, new cutting materials and geometries are developed. In this case, four types of silicon nitride based ceramics are investigated after coating with CVD-diamond for the use as ceramic end mills. To assess the wear resistance, model wear tests and damage evaluation were carried out and evaluated. After subsequent summary of the results, ceramic and cemented carbide substrate were selected for milling of glass and carbon fiber reinforced plastic (GFRP/CFRP) The determined force distribution and wear properties of the tools are presented and discussed. The diamond coated substrates are qualified by their wear profile and the measured constant cutting forces for use in the machining of GFRP/CFRP. Finally, the crack formation progress for diamond coated silicon nitrides when machining glass and carbon fiber reinforced plastics was demonstrated.

Wear Behavior of Carbonitrided and Nitrided Hot Working Steels*

Abstract During forging the tools have to resist high thermal and mechanical loads. Therefore, forging dies are usually nitrided in order to increase the wear resistance of the surface areas. Compared to nitriding carbonitriding increases the hardness depths in shorter treatment times. Due to the (carbo-)nitriding, the surface near region gets a better hot hardness and a better wear resistance than the untreated material. In a second process step by nitriding after carbonitriding, a wear and corrosion resistant compound layer can be created at the surface. In the present work the wear behavior of carbonitrided and nitrided hot working steel ENX38CrMoV5-3 (1.2367) was investigated. The evaluation concerning abrasion and thermal fatigue in the contact of forging die and workpiece was carried out by model wear tests like the two-disc test (Amsler test), the ball-on-disc test and a cyclic induction heating and quenching. The conditions of the heating cycles were chosen close to the forging process. The surface areas were investigated after several cycles in order to gain information about the mechanisms of the surface modification. Finally, the treatment combination carbonitring/nitriding was transferred to forging dies and the wear behavior was investigated in fatigue-life experiments under application conditions.

Description of the Experimental Method and Procedure of Model Wear Test of Refrigeration Compressors’ Parts

Friction nodes in refrigeration compressors are lubricated with a mixture of lubricating oil and refrigerant. The concentration of refrigerant in oil depends on temperature and pressure of the refrigerant. Determining the effect of this mixture on the size of wear in refrigeration compressors in laboratory conditions is only possible through an accurate reflection of friction parameters.The authors managed to prepare a prototype stand for a tribological test with a model block-on-ring friction node and the high-pressure chamber allowing for simulated conditions in refrigeration compressors. The present paper includes the description of the experimental method and procedure of model wear test of refrigeration compressors parts. The study itself constitutes the basis for the verification tests of the stand.

The Effect of Ti Addition and Aging on Wear Behavior of AlMgSi Alloys Reinforced with In Situ Al3Ti Particles

The purpose of this study is to investigate the effects of Ti addition (1 and 2% Ti) and aging heat treatment on the mechanical and wear characteristics of Al-12Si-20Mg cast alloys. In preliminary studies conducted to determine the aging parameters, cast alloys were kept at 550 °C for 2 h before being quenched into water and aged at 200 °C for five different periods (3, 6, 9, 12, and 15 h). As the specimen aged for 12 h had the highest hardness value, all the specimens were aged at 200 °C for 12 h. The microstructures of the as-cast and aged specimens were analyzed using an optical microscope and a scanning electron microscope. The hardness of the investigated alloys was measured by micro-hardness test. The wear tests were carried out using the pin-on-disk model wear test apparatus, and the results were evaluated according to weight loss. According to the wear test results, the wear behavior of the investigated alloys changed depending on the aging heat treatment applied and the load. While Ti addition and the aging heat treatment applied reduce the weight loss at low loads (5 N), they increase the weight loss at higher loads (10 and 20 N).

Industrial use of plasma-deposited coatings for components of automotive fuel injection systems

Modern fuel injection systems for cars consist of precise mechanical parts, which need solid lubricant coatings to be protected from friction and wear. Diamond-like-carbon (DLC)-coatings show crucial advantages in a low wear (see the high hardness), in the low coefficient of friction (even for a non-lubricated contact with steel as a counterpart) and in the low wear of the counter body. Several examples of applications of DLC-coatings are discussed. Model wear tests like the oscillating wear test are suitable for various tribological applications like “piston in a cylinder” or “valve lifter on a camshaft”. To get a reproducible contact between the two parts in a tribological contact, a running-in process for the oscillating wear test was developed. In order to design powerful systems and find cost-saving solutions shortly, coatings should be used as constructional elements for mechanical systems. The integration of coatings into the modeling and simulation of precise mechanical systems will be discussed for an application with impact wear. The importance of surface engineering as “the application-specific design of the surface (with a coating) and the component-part as a system with high performance in the interaction with the surroundings” will be emphasized.

The effect of precipitation-hardening conditions on wear behaviours at 2024 aluminium wrought alloy

In this study, wear behaviours of 2024 aluminium wrought alloy were investigated in different tribological conditions based on its ageing conditions. For this purpose, the alloy aged in five different temperatures and periods (at room temperature for 1 week, at 120 °C for 24 h, at 150 °C for 18 h, at 160 °C for 16 h, at 200 °C for 2 h) was worn in pin-on disc model wear test apparatus using different abrasive grit size (5, 11, 18 and 30 μm SiC papers). Furthermore, the effects of different sliding speeds (0.078, 0.156, 0.208 and 0.338 m s −1) and loads (6.45, 9, 9.3 and 11 N) on wear resistance were also examined. It was measured amounts of mass loss and examined worn surfaces. The mass loss of the specimens increased with load and the abrasive grit size.

Wear of soft tool materials in sliding contact with zinc-coated steel sheet

In order to reduce costs of tooling for press operations, efforts are made to use alternative tool materials like wood or plastic. Friction and wear characteristics in sliding contact with zinc-coated steel sheet could, however, limit the applicability of these tool materials for automotive applications. In this work the wear resistance of alternative tooling materials is studied by a combination of forming tests at a high speed stamping line and model wear tests using the TNO slider-on-sheet tribometer. With this tribometer, volume loss of alternative tooling materials can be determined as a function of the sliding distance, using sheet materials from automotive practise. Results show that the wear rate of a soft tool material can change two orders of magnitude as a result of the zinc layer type used. Furthermore, it is shown that the relative performance of alternative tool materials is strongly related to the hardness of the (tooling and sheet) materials. Industrial forming tests with a selection of alternative tooling materials confirmed the model wear test results. The same ranking of the tooling materials with respect to volume loss is obtained per sheet material.

The effect of lubricant selection on galling in a model wear test

Galling is a known failure mechanism in sheet metal forming (SMF) processes. As a result of this wear process, the amount of waste increases, the production process becomes hard to control and eventually expensive maintenance is required in order to continue production. Delaying or avoiding galling mechanisms by optimising the contacting materials and lubricant is therefore of high industrial importance. The presented work focuses on the effect of lubricant selection on galling, using a model wear test: the TNO slider-on-sheet tribometer. With this tribometer, galling mechanisms are studied using tool steel in sliding contact with lubricated deep draw steel DC 06. The wear data obtained with the test method agrees well with a general framework of lump initiation, lump growth and scoring (galling). Experimental data clearly demonstrates that a low coefficient of friction at the start of the experiment is not a reliable indicator for galling prevention. Hence, lubricant evaluation should be done based upon long-term testing instead of on short-term testing. Comparative results with a lubricant set shows that the TNO slider-on-sheet model wear test is suited for ranking forming lubricants with respect to their ability to avoid material transfer.

Chrome Nitride Coatings for Applications in Plastics Processing

Abstract Coated moulds, especially cavity surfaces and ejection parts are state of the art in plastics processing. Regarding the plastification unit i.e. screws and barrels coatings are not well established. Wear in processing remains a problem, especially when no abrasion is permitted e.g. in manufacturing optical elements. The surfaces must resist the abrasion of hard glas fibres as well as the corrosive attack of the polymers. Electroplated chrome is one of the answers to these demands, because of its hardness and corrosion resistance. Another solution are thin hard coatings which are not yet well established. Titanium nitride produced by PVD technique was found to show excellent abrasion resistance but often not sufficient corrosion properties. Chrome nitride was found to have great hardness like TiN, corrosion resistance behaviour similar to electroplated chrome and in contrast to electroplated coatings no tensile internal stress. The present study deals with the spectrum of characteristic properties of CrxN coatings like hardness, adhesion, internal stress, chemical composition and phases produced by PVD magnetron sputtering. The coatings were deposited on steel, described in characteristics and tested in a model wear test with plasticized moulding material (PA 66-GF50 and others) simulating the tribological situation between screw and barrel of extruders or injection moulds. The tribological behaviour was studied after the complex test procedure. The high temperature of the plasticized material, high abrasion by glas fibres and corrosive influence could only change the coatings properties of CrxN slightly.

Wear resistance of hard coatings in plastics processing

The degree of machine wear decisively determines the economic feasibility of plastics processing. The high temperature of plasticized material, high abrasion by fillers and corrosion attack will remain a problem. In addition, quality loss caused by wear products frequently becomes unacceptable and makes it necessary to shorten maintenance periods for replacing the worn components. The potential of hard coatings for wear protection in plastic processing units is investigated in the present study. Model wear tests were carried out to demonstrate the tribological situation inside the screw/barrel system of extruders and injection moulding machines. The test methods covered the solid and the molten state of various moulding compounds. In comparison with standard metals used for screws and barrels, the results show that, in general, hard coatings prepared by physical vapour deposition (PVD) and chemical vapour deposition (CVD) offer a good opportunity for wear protection: not so much in the solids conveying zone but more so in the melting zone. Furthermore, the results depict a dependence on the plasticized moulding compounds.

Concepts for presses and tooling for metal injection moulding: U.Haupt, H.Walcher. (Arburg GmbH, Germany.)

The degree of machine wear decisively determines the economic feasibility of plastics processing. The high temperature of plasticized material, high abrasion by fillers and corrosion attack will remain a problem. In addition, quality loss caused by wear products frequently becomes unacceptable and makes it necessary to shorten maintenance periods for replacing the worn components. The potential of hard coatings for wear protection in plastic processing units is investigated in the present study. Model wear tests were carried out to demonstrate the tribological situation inside the screw/barrel system of extruders and injection moulding machines. The test methods covered the solid and the molten state of various moulding compounds. In comparison with standard metals used for screws and barrels, the results show that, in general, hard coatings prepared by physical vapour deposition (PVD) and chemical vapour deposition (CVD) offer a good opportunity for wear protection: not so much in the solids conveying zone but more so in the melting zone. Furthermore, the results depict a dependence on the plasticized moulding compounds.

Functional behaviour of PVD coatings under sliding and rolling stress conditions

AbstractWhereas wear‐resistant PVD coatings are well established in the field of metalcutting, and the functional and tribological behaviour of these coatings is well known under such conditions, PVD coatings are used only occasionally in mechanical engineering. The reason for this seems to be the lack of information concerning the functional behaviour of these coatings in closed tribosystems.To evaluate new areas of application together with optimised coating compounds, model wear tests were performed under sliding, rolling and slip‐rolling stress conditions. In addition, the test parameters, such as sliding speed, load, ambient temperature, and number of revolutions were varied, as were the coating compounds and their thicknesses.The results obtained show that friction and wear of PVD coatings are both strongly influenced by the kind of stress and the test parameters themselves. Coatings that perform well under certain test conditions can break down quickly under some other stress conditions. TiN coatings, for example, which display low friction and wear under sliding friction, fail under rolling conditions very shortly afterwards.

PVD CrxN coatings for tribological application on piston rings

Abstract Besides the established PVD coatings for the wear protection of machining tools, this paper deals with coating development and model wear test results from PVD coatings on piston rings for combustion engines. Piston rings are examples for the application of thin films on commonly used mechanical components. The PVD Cr x N coatings are deposited by RF magnetron sputtering and characterized by their fundamental mechanical properties like thickness, hardness, residual stress and adhesion, which are important for the tribological behaviour of the coating substrate compound. The contact mechanics of the tribological system piston-ring–cylinder are determined by high mechanical loading and changing geometry caused by the sliding kinematics. Therefore, the range of thickness is about 7 μm. The selected rings are made of steel DIN 1.4112 (DIN X 90 Cr Mo V 18) with a bore diameter of 97.5 mm. The results of the coating substrate characterization — high hardness, moderate compressive residual stresses and sufficient adhesion on metallic substrates — provide good behaviour of coatings in this tribological application. This is confirmed by the results of the tribological test procedures which have been performed with ring-on-disc model-wear tests and a short-stroke test rig.

Influence of different production parameters on the functional behaviour of tools and parts after coating

The efficiency of using wear-resistant coatings for tools and components depends considerably on the adhesion between the coating and the substrate. Therefore we investigated how different production parameters of the substrate influence the functional behaviour of tools and machine parts after coating. Before coating by physical and chemical vapour deposition processes (PVD, PACVD and CVD), the surfaces of tools and parts were differently machined to obtain different roughnesses, topographies and residual stresses in the substrate. The surfaces were carefully examined before and after coating by measuring their surface roughnesses and residual stresses. The surfaces were investigated by modern surface analysis (SEM, AES, ESCA) in order to detect coating defects and to obtain information about the chemical composition of the coated surface or the coating itself. Finally, the functional behaviour was checked by cutting, forming and model wear tests under laboratory and field conditions. Applied tests with vane pumps were also carried out. The examination of the results of all the tribological tests shows that the functional behaviour of coated model wear specimens, tools and parts depends strongly on the surface conditions of the substrate before coating. According to the type of stressing, different surface pre-treatments are recommended. The tribological behaviour is influenced by the interaction of many different parameters, such as the surface roughness and topography and the residual stress in the coating and substrate. With optimized surface pre-treatment of the substrate, the life of coated tools or parts can be increased considerably.

Simulation of the tribological behaviour of components and cutting tools by means of model wear testing

AbstractModelling the wear test process can initiate real‐life friction and wear of components and cutting tools. In this paper we describe model wear tests that were developed to discover (a) whether or not simulation of the wear processes that occur during cutting is possible, and (b) how the wear of indexable inserts can be reduced by using thin hard coatings, e.g. TiN, (Ti,Al)N, Ti(C,N) when milling metallic materials. The real‐life wear of the track groups of various tracked vehicles was also investigated, in order to evaluate the wear resistance of certain materials.

Abrasive wear resistance and cutting performance of complex PVD coatings

In recent years the development of physical vapour deposition coatings for improved wear resistance of cutting tools is turning to more complex coating systems. Different multilayer systems are offered in addition to binary, ternary and quaternary monolayer coatings. Their variety makes it impossible to test all possible coatings under real machining conditions. Model wear tests such as the Taber Abraser test can help in preselecting the coatings with a good potential to perform successfully. In this paper we compare the results of the Taber Abraser test of different multicomponent and multilayer coating combinations within the system Ti-Zr-C-N with the results of cemented carbide indexable tips in interrupted-cut machining. It is shown that the results of both examinations often correlate and that abrasive wear tests can be used to give information about the potential of coatings under special cutting conditions.

Possibilities of model wear testing for the preselection of hard coatings for cutting tools

Abstract The wear behavior of indexible inserts for milling metallic materials was simulated by means of a modified pin-on-disc system. An original indexible insert was used as the stationary specimen (pin), while the rotating specimen (disc) was made of the workpiece material. Physical vapour deposition coatings of TiN, (Ti,Al)N, (Ti,Cr)N, (Ti,Zr)N, Ti(C,N), CrN and ZrN were examined. The discs were made of an Ni-Fe alloy, steel SAE 1045 or copper. The results of the tribological behaviour of the Ni-Fe alloy and the steel SAE 1045 discs agreed satisfactorily in the milling tests and the model wear tests. With copper discs, a significant decrease in the wear of the indexible inserts was only detected in milling tests. By making broader grooves into the copper discs, perpendicular to the sliding direction, The sliding process was periodically interrupted. This change led to a qualitative agreement between the milling and model wear tests. The results reveal that the simulation of the wear behaviour of cutting tools is possible, but the results have to be verified by cutting tests.

Physical vapour deposition of complex hard coatings on ceramic substrates

Today there exists only a little information about hard coatings obtained by physical vapour deposition (PVD) on ceramic substrates. The aim of the PVD coating on ceramic substrates is a further improvement of the material properties, e.g. wear resistance. Coatings have been deposited by reactive magnetron sputtering on silicon nitride (Si 3N 4), aluminium oxide (Al 2O 3) and Al 2O 3 + TiC ceramic. As a reference, coated high speed steel and cemented-carbide substrates have been used. Coating systems were complex hard materials of the Cr-Al-C-N and Ti-V-C-N systems. R.f. bias allowed the deposition of these coatings on electrically insulating substrates. Mechanical characterization of the coatings has been made by determination of hardness, critical load and impact load (coating impact test). Scanning electron microscopy investigation of the rupture structure and X-ray diffraction allowed the determination of the coating-substrate microstructure. Model wear tests gave information on the wear resistance of the coated ceramics, and annealing tests verified thermal stability.