Neuentwicklungen für den Verschleiß‐ und Korrosionsschutz beim Plasma‐Pulver‐Auftragschweißen

New developments for wear an corrosion protection by weld surfacing with plasma transmitted arc process Highly wear‐resistant claddings which contain carbides can be applied by weld surfacing with the PTA process. The use of vanadium carbide prevents undesirable reactions with the matrix material. Thus, highly corrosion‐resistant Fe‐based claddings can be produced for applications in the food and marine industries, and Ni‐based claddings can be applied to components exposed to inorganic acid attack. A combined test is applied for determining the relative effect of corrosion under combined exposure to abrasive wear and corrosion and indicates the primacy of abrasive wear for behaviour in operation.     

Entwicklung hochverschleißbeständiger wolframschmelzkarbidbasierter Schichten auf Aluminiumbauteilen durch Plasma‐Pulver‐Auftragschweißen

Development of high wear‐resistant FTC‐based coatings on aluminium components using plasma transferred arc welding Nowadays, functional surfaces of components can be effectively protected from extreme wear with the help of fused tungsten carbide (FTC) coatings. The wear protection of steel components using FTC has been well known for many years. This paper presents the feasible study of improving the wear resistance of aluminium components with FTC particles using plasma powder arc welding. The FTC coatings are developed with two methods: one is the dispersion of carbide particles in aluminium and the other one is the combination of dispersing and alloying of FTC‐based composite powders. In this research, coatings within a thickness range of a few millimeters are developed with varying process parameters and compositions of the filler materials. The developed coating systems are tested with regard to their specific properties and their wear resistance. Finally, their application potential is presented.     

Synthesis and characterization of functionally graded nickel‐nickel coated ZrO2 composite coating

Electroless‐nickel plated ZrO₂ (NCZ) particles have been used to produce a functionally graded nickel‐electroless‐nickel plated ZrO₂ composite coating. So, electroless‐nickel plated ZrO₂ particles concentration was continuously increased from 0 to an optimum value in the electroplating bath (Watt's bath). The substrate was ST37 steel and the thickness of the coating was approximately 50 μm. Also a uniformly distributed nickel‐electroless‐nickel plated ZrO₂ composite coating has been manufactured as comparison. The composite coatings were characterized by scanning electron microscopy and energy‐dispersive X‐ray spectroscopy. Structure and phase composition were identified by X‐ray diffraction analysis. Microhardness of the coatings was evaluated by employing a Vickers instrument. Three‐point bend test was carried out to compare the adhesion strength of the coatings. Dry sliding wear tests were performed using a pin‐on‐disk wear apparatus. The electrochemical behavior of the coatings was studied by electrochemical impedance spectroscopy. The microhardness measurements showed that, with increasing the co‐electrodeposited electroless‐nickel plated ZrO₂ particle content in the nickel matrix, the microhardness increases from interface towards the surface of the functionally graded composite coating. Bend, wear and electrochemical test results confirmed that the functionally graded composite coating has higher adhesion, wear resistance and corrosion resistance as compared with the uniformly distributed coating. This has been attributed to lower mechanical mismatch between coating and substrate in functionally graded composite coating with respect to the uniformly distributed one.     

Rezyklieren von metallischen Spänen mittels Electro‐Discharge Sintering

Composite material Ferro‐Titanit^® is produced powder‐metallurgical by Deutsche Edelstahlwerke GmbH (DEW) and is commonly used for wear and corrosion resistant component parts. Materials properties can be attributed to the microstructure which consists of a corrosion resistant metallic matrix and a huge amount of approx. 50 vol.% of hard Ti‐monocarbides. Although Ferro‐Titanit^® possesses a high amount of hard particles, the material can be machined by turning and drilling in solution annealed condition. Due to the alloying content (Mo, Cr, TiC) of Ferro‐Titanit^®, there is a high motivation to recover those elements by a recycling process of the chips, thus expensive and limited resources can be saved. On idea of a recycling process can be found in the redensification of those chips by electro discharge sintering (EDS). In this work, chips of the material Ferro‐Titanit^® were densified by EDS technique and the resulting microstructure was investigated by optical and scanning electron microscopy. Furthermore, microstructure and hardness of the EDS densified specimens was discussed with regard to the microstructure of conventionally sintered Ferro‐Titanit^®‐samples in laboratory conditions.     

Grundlagen,Herstellung und Anwendungsaspekte des Supersolidus Flüssigphasensinterns von hochlegierten Werkzeugstählen und Metallmatrix‐Verbundwerkstoffen

Principles, manufacturing and application aspects of super solidus liquid phase sintering of high‐alloyed tool steels and metal matrix composites Iron‐based metal matrix composites (MMC) are applied for abrasive wear resistant applications. A common production route uses hot isostatic pressing (HIP) of metal and carbide powders, a comparatively cost intensive process. Using high‐alloyed tool steels as matrix materials it is possible to obtain dense materials by liquid phase sintering with an internally formed liquid phase. This contribution describes the basic principles of densification of the matrix materials taking thermodynamic calculations into consideration. It points out a production route for processing particulate reinforced, high wear resistant composite materials by sintering. Beside the sintering behaviour concepts for heat treatment as well as the abrasive wear resistance are discussed.     

Strangpressen von verschleißbeständigen Fe‐Basis MMC

Hot extrusion of wear resistant Fe‐base metal matrix composites (MMC) Increasing demands on technical surfaces, i.e. thermal load, corrosion or wear, often prompt the development of tailored materials or coatings. In highly abrasive environments the progress in powder metallurgy has lead to the production of highly wear‐resistant materials based on metal‐matrix composites (MMC). Such materials are produced from a metal matrix (MM) based on Fe, Ni or Co and additional hard phases (HP), such as carbides, nitrides, borides or oxides. Moreover, powder metallurgical techniques can be used to adapt the particle size, the distribution and the content of the hard phases to the wear system on a large scale. HIP cladding is an established method of producing such MMC, but due to its near net shape capsule technique it is quite expensive. Because of this reason hot direct extrusion of capsules filled with powder blends was researched in a DFG‐Project as a method of producing long cylindrical products. Aiming at a high abrasive wear resistance, powder blends of hardenable steels with additions of fused tungsten carbide (WSC) or titanium carbides (TiC) were used. The extruded MMC were investigated with respect to their densification and microstructure, their bending strength and their wear resistance.     

Gefüge und magnetische Eigenschaften von Chromgusseisen für Mahlkugeln

Microstructure and magnetic properties of white cast irons for grinding balls Many types of cast ferrous alloys are used for applications in the grinding, crushing, mineral‐handling and earthmoving industries. The finish grinding process for cement materials uses ball mills with differently sized grinding balls. This work deals with grinding balls of high chromium white cast irons with various chemical composition. Using certains thermal treatments, the influence of parameters of microstructure on abrasive and impact wear resistance has been studied. A special test system has been adapted for the assessment of the impact properties of these alloys. Examination of the carbides were performed using a transmission electron microscope. Additional microstructural examinations were made using the Scanning electron microscope. For a nondestructive inspection of the grinding balls, the possibilities of using the magnetic characteristics for determining the structural state and mechanical properties of white cast irons are analyzed. The results showed that the hardness and the dynamic fracture toughness are important for the combined impact‐abrasion resistance. It has been established that the microstructure has a decisive influence on the magnetical properties of white cast irons.     

Improvement of wear resistance behaviour of laser metal deposited Ti6Al4V/Mo composites

Titanium and its alloys are materials found to exhibit wonderful properties such as its lightweight and, excellent mechanical properties – tensile strength and toughness even at elevated temperatures, extraordinary corrosion resistance behaviour and ability to withstand high temperatures. These unique properties have made Ti6Al4V attractive for a range of industrial applications. Some of the successful applications include medical implants and prosthesis, connecting rods for automotive, aerospace, oil and gas, sports equipment, gas turbine engines and space crafts. However, the high cost and poor wear resistance of Ti6Al4V limits its use for specific applications. This study investigates the wear resistance of the laser deposited Ti6Al4V composite and its enhancement with molybdenum. In this study, the Ti6Al4V/Mo composites were produced, the effect of influencing process parameter was investigated, and the produced Ti6Al4V‐Mo composites were further examined through various tests. The results revealed that the Ti6Al4V/Mo composite produced at varying laser powers had improved wear resistant when compared to the Ti6Al4V substrate. A direct correlation between the wear resistance and hardness was also observed.     

Herstellung und Untersuchung des Verschleißverhaltens von induktiv eingeschmolzenen Hardpaint‐Schutzschichten

Friction and wear processes generate significant economic damage annually in industrial production due to maintenance and repair costs as well as loss associated with production downtime. Wear‐resistant coatings are a measure for reducing wear. In this context, the novel hardpaint technology for coating of parts with a fusible metal powder composition is described. Components with complex geometries as well holes or undercuts can be coated easily and inexpensively. Two protective layers are discussed and characterized in terms of their microstructure. Density measurements, hardness tests and scanning electron microscopic investigations were carried out. Both powder layers were inductively melted after application and are based on a hard alloy (iron‐based) commonly used for plasma transferred arc powder surfacing. Abrasion wear resistance is evaluated based on the results of the wear tests and microstructural investigations. Furthermore the results are discussed in comparison to a martensitic fine‐grain steel (Hardox 450), which is commonly used in abrasively stressed areas. Compared to Hardox 450 both hardpaint coatings have a much more wear‐resistant behavior due to their hard phases. In addition, it was confirmed that the hardpaint technology is able to embed thermally sensitive fused tungsten carbides which are significantly increasing the wear resistance against abrasion.     

Zum Einfluss des Schweißens auf das Kriechverhalten moderner Stähle für die thermische Energieerzeugung

The influence of welding on creep behaviour of modern steels for thermal power generation Un‐ and low alloyed ferritic/bainitic Chromium steels as well as high alloyed ferritic/martensitic 9–12 % Chromium steels are widely used for high temperature components in thermal power generation. Welding in all its variety is the major repair and joining technology for such components. The weld thermal cycle has significant influence on the base material microstructure and its properties. The Heat Affected Zone is often regarded as the weakest link during high temperature service. While weldments of un‐ and low alloyed ferritic Chromium steels can show significant susceptibility to Reheat Cracking in the coarse grained heat affected zone, weldments of high alloyed ferritic Chromium steels generally fail by Type IV Cracking in the fine grained heat affected zone during long term service. In this paper the influence of the weld thermal cycle on the base material microstructure is described. Long‐term creep behaviour of weldments is directly related to the main failure mechanisms in creep exposed ferritic weldments and implications for industries using heat resistant ferritic steels are shown.     

Eigenschaften und Anwendungen von Chemisch Nickel‐Dispersionsschichten

Properties and applications of electroless nickel composite coatings This paper discusses the variety of composite electroless coatings used in different industrial applications. The inclusion of particulate matter within electroless nickel deposits can add entirely new properties to the plated layer. Composites with hard particles like diamond, silicon carbide and boron carbide provide greater wear resistance and the possibility for adjustable friction properties. Composite electroless nickel with diamond or ceramics has found wide applications in the textile, automotive and mechanical engineering industry. Friction joints in automotive engines constitute an important field of application for diamond coatings. Modern internal combustion engine designs require that the crankshaft and camshaft be fitted at a specific relative angle. In order to establish the correct angle during assembly and maintain it over the life of the engine, axial press‐fit joints in combination with centrally located retention bolts are employed. Failure of either the joints or the bolts can result in serious damage to the engine. The torque transfer ability of these engine components can be significantly increased by incorporating a friction foil that is diamond‐coated on both sides. Composite coatings with coarser diamond particles can be used for the coating of precision tools in the semiconductor industry. Enhanced lubricity can be achieved by incorporating solid lubricants in electroless nickel deposits. Composite coatings with PTFE or PFA offers non‐stick surfaces with antiadhesive properties and good resistance against adhesive wear. Because of the temperature and softness limitations these coatings are best suited for lower temperature and light loading applications. Electroless nickel boron nitride coatings can withstand temperatures up to 600 °C. This coating reduces coefficient of friction and wear in dynamic applications. A further application is the coating of molds for rubber and plastic components.     

Influence of electron beam deflection techniques used during the cladding process on the wear and corrosion behaviour of cobalt‐based protective coatings on austenitic stainless steel

The present work aims to improve the wear resistance of the austenitic stainless steel X6CrNiMoTi17‐12‐2. In view of the potential use of this alloy, however, corrosion resistance should be maintained where possible. An electron beam surface treatment (cladding) was performed, and the cobalt‐based alloy Stellite® 12 was used as the wear‐resistant material. The presented results show the effects of several electron beam oscillation figures during the cladding process with regard to layer bonding, microstructure formation and hardness. The surface hardness achieved was 576±18 HV 0.3, almost three times higher than that of the base material (203±3 HV 0.3). The scratch energy density – which represents the resistance to abrasive wear – could be increased by a factor of 1.5. Under abrasive‐adhesive stress loading conditions, the determined wear volume decreased by a factor of almost 5. Based on the corrosion investigations carried out, it was possible to prove that in comparison to the base material, the tendency towards pitting corrosion could be almost completely suppressed.     

Verschleißreduzierung an Matrizen für das Präzisionsschmieden von Zahnrädern durch Mehrlagenhartstoffbeschichtung (TiN‐TiCN‐TiC)

Wear reduction on dies for precision forging of gear wheels by means of multi‐layer coating (TiN‐TiCN‐TiC) Due to high thermal, mechanical and tribological loads the tool life quantity of hot forging dies compared to other manufacturing processes is relatively low. Depending on the number of forged parts the mentioned loads lead to different failure causes of the dies. In this connection wear is the main failure cause of hot forging dies. Especially in the precision forging process of gear wheels with its exacting tolerances the tool life quantity is low, which leads to often interruptions of the production process. Because wear concentrates on the near‐surface die areas, these problems can be reduced by increasing the wear resistance of these areas by the Duplex PACVD‐Method, which means nitriding and multi‐layer coating (TiN‐TiCN‐TiC).     

A study of casting high‐boron high‐speed steel roll materials

In this paper, we design and prepare five kinds of high‐boron high‐speed steel roll materials. The microstructure, mechanical property and wear resistance of high‐boron high‐speed steel roll materials were studied by means of optical microscopy (OM), scanning electron microscopy (SEM), X‐ray diffraction (XRD) and hardness measurement, impact test and abrasion test. The results show that as‐cast microstructure of high‐boron high‐speed steel consists of martensite, retained austenite and borocarbide. Hardness of as‐cast high‐boron high‐speed steel excels 64 HRC. In unmodified high‐boron high‐speed steel, eutectic borocarbide is distributed in a network along the grain boundary. With the addition of RE‐Mg‐Ti compound modifier, the networks of borocarbide is broken. The hardness of high‐boron high‐speed steel gradually decreased with the increase of tempering temperature. Under the same conditions, the impact toughness of unmodified high‐boron high‐speed steel roll material is slightly lower than that of modified steel. The wear resistance of modified high‐boron high‐speed steel roll material is greater than that of high‐carbon high‐vanadium high‐speed steel roll.     

Development of Wear and Corrosion Resistant Metal Matrix Composites with hard Particles formed in Situ

Metal matrix composites (MMC) were developed, consisting of hardenable steel matrices and embedded particles of titanium nitride (TiN) or vanadium nitride (VN) formed in situ during the consolidation by hot isostatic pressing (HIP). Designing wear and corrosion resistant materials was the objective of this development. The materials were produced by means of powder metallurgy and are composed of a ferrritic stainless steel powder X4CrMo15–1 and crushed particles of ferro titanium or ferro vanadium, respectively. These powder mixtures were first heat treated in an N₂‐atmosphere for alloying with nitrogen and subsequently consolidated to wear resistant MMC by HIP. This publication describes the necessary processing steps, taking into account thermodynamic equilibrium calculations with Thermo‐Calc.     

Die γ2‐Phase und ihre Effekte auf die Eigenschaften heterogener Mehrstoffaluminiumbronzen

The γ₂‐Phase and their Effects on the Properties of Complex Aluminium Bronzes In this report the effects of the chemical composition and of the processing on the microstructure and some properties of complex aluminium bronzes are presented. Especially the formation and the forms of the γ₂‐phase in the microstructure and relationships between the microstructures and the properties of the alloys are described.     

Schweißen von Hohlstrukturen und offenporösen Metallschäumen für den Einsatz in Kombi‐Kraftwerken

Welding of Hollow Structures and Open‐Porous Metal Foams for Application in Combined Cycle Power Plants For applications within the scope of novel cooling concepts joining technologies for sandwich composites and open‐porous metal foams are researched in the context of the Collaborative Research Centre 561 “Thermally highly loaded, porous and cooled multi‐layer systems for combined cycle power plants”. The research motivation and application fields of the different structures are defined. Welding processes and strategies for manufacturing these structures are specified as well as the joining technologies’ characteristics. Planned future works for enhancements of the processes and structures are listed.     

Einfluss unterschiedlicher Oberflächenzustände vor dem Plasmanitrieren auf Eigenschaften und Zerspanungsverhalten des Schnellarbeitsstahls S 6‐5‐2

Surface states and wear behavior of drills of ground, sandblasted and plasmanitrided samples and drills made of AISI M2 high speed steel In the present work the effect of different surface conditions on plasma nitriding response of AISI M2 high speed steel was investigated. The plasma nitriding of ground and sandblasted samples and drills was performed at temperatures of 400°C and 500°C for two gas mixtures: 5 vol.% N₂ and 76 vol.% N₂ in hydrogen. Surface layers were characterized before and after plasma nitriding concerning the microstructure, roughness, microhardness, chemical composition, phase composition and residual stress states. Machining tests were carried out with drills during which drilling forces and flank wear have been measured. A significant effect of the surface state prior to nitriding on residual stress states and the properties of the nitrided layer and untreated core has been observed. Thinner nitrided layers on ground and sandblasted samples were attributed to high compressive residual stress states and a stress affected diffusion of nitrogen and carbon. In the machining tests, sandblasted drills exhibited the best performance. Lower nitrogen concentrations in the gas atmosphere without the formation of a compound layer gave the lowest drill flank wear for sandblasted surfaces while higher nitrogen concentrations led to a reduction of drilling forces and torque.     

Microstructures and corrosion resistance of as‐cast aluminum‐10 wt.% silicon and aluminum‐20 wt.% silicon alloys

The microstructures and corrosion resistance of two as‐cast alloys, aluminum‐10 wt.% silicon hypoeutectic alloy and aluminum‐20 wt.% silicon (weight percent) hypereutectic alloy are investigated by conventional casting, the scanning electron microscope equipped with oxford X‐ray energy dispersive spectroscopy system and transmission electron microscope are applied for analysis. The results show that the microstructures change from the strip‐like into lump shape with the increase of silicon content from 10 % to 20 %. The electrochemical polarization curves prove that the aluminum‐20 wt.% hypereutectic silicon alloy had the better resistance with the corrosion potential of ?1.414 V and corrosion current density of 5.41 ? 10^?5 ampere compared with the aluminum‐10 wt.% silicon hypoeutectic alloy.     

Microstructure and wear resistance of spray formed and conventionally cast high‐chromium white iron

A billet of hypoeutectic high‐chromium white iron (19% Cr, 2.5% C) was spray formed using Gas‐to‐Metal Ratios (GMR) of 0.9, 1.0, and 1.1. Microstructural studies and dry sand rubber wheel abrasion tests were carried out, on the one hand, to compare between the spray formed and conventionally cast material and, on the other hand, to investigate the relationship between gas‐to‐metal‐ratio, eutectic carbide morphology and abrasion resistance. The spray formed material was characterized by a considerably finer carbide morphology (max. ?30 μm) than the conventionally cast material (max. 100–200 μm). The coarser carbide morphology is believed to be responsible for the superior abrasion resistance of the conventionally cast material. Although the carbide morphology of the spray formed material was only moderately influenced by the changes in the gas‐to‐metal‐ratio, there was a clear improvement in the abrasion resistance with decreasing gas‐to‐metal‐ratio. The improvement correlated with a decrease in the fraction of very fine (<1.5 μm) carbides, rather than with an increase in the mean carbide size.