In Laser Cladding, a differentiation must be made between cladding by brazing and cladding by welding regarding process parameters and the resulting material properties. Results of investigations of bronze cladding on steel parts produced by Laser Deposition Brazing will be presented. This means that a strong metallurgical bond is realized by diffusion processes by Laser Deposition Brazing, but the steel base material is not molten. The coatings were characterized by hardness distribution measurements from the bronze cladding to the steel substrate, by measuring the size of the heat-affected zone and by porosity measurements. This combination of a steel substrate and a local bronze coating is used industrially in many tribological applications, such as plain bearings or hydraulic pumps etc. The bronze offers excellent tribological properties. In some cases, the bronze is used as a complete solid part. However, applying the bronze locally to a steel base body instead of using a complete solid bronze component, offers the advantage of the higher modulus of elasticity of the steel, which provides greater stability of shape with regard to possible elastic deformations as these coated parts are exposed to high mechanical loads, it is essential that a high coating quality is achieved by laser cladding and that the properties are extensively and purposefully characterized. The production technology, the characterization and the industrial applications of such bronze coated steel parts are presented and explained in this contribution.

Hydrodynamic bearings have to fulfill different requirements, depending on the operating conditions. Yet, conventional hydrodynamic bearings could not be used in critical operating conditions such as permanent start / stop operations. This is the reason why rolling bearings are currently used for frequent starting operations and low circumferential velocities, as they occur in wind turbines. In order to operate hydrodynamic bearings in a fail-safe manner even under these increased requirements, new bearing materials are needed. Within this study two new bearing material concepts are developed and deposited by thermal spraying as coatings to interact in this tribological system. On the one hand, matrix materials containing friction-reducing solid lubricants and on the other hand, multilayer systems, which can be used in as-sprayed condition, are investigated. The aim of both concepts is to improve the operation properties under critical conditions. The coating concepts are therefore tested on a modified high-load ring-on-disc tribometer and are compared to a reference plain bearing material produced by conventional casting. In this way, it is shown whether these new concepts can meet the requirements of slow-moving and highly loaded hydrodynamic bearings.

In state-of-the-art manufacturing of sliding bearings, brass components are soldered to respective parts, which is costly and energy-intensive. Furthermore, up to now most bearings still contain lead, which by EU regulations for new part has to be omitted due to associated health risks. Cold spraying can be employed as additive manufacturing technique and opens the perspective to deposit the requested bearings in desired leadfree layout where needed. Aside cohesion and tribological behaviour, sufficient adhesion of the coating is essential for applications. The present study aims to systematically elucidate the influence of surface roughness on adhesion. The surface roughness was adjusted by varying the grit blasting material, grit size, blast pressure, blast distance and substrate material with the aim to study influences by impact conditions, surface topography on particle deformation and bonding in cold spraying. The results show that the adhesion strength reaches a maximum for a certain roughness. The ideal surface roughness to ensure good adhesion of cold-sprayed coatings apparently depends on specific impact conditions related to the powder material strength but also on the substrate material strength and particle size distribution. By systematic tuning of blasting conditions, coating adhesion can be increased by about a factor of two, thus meeting the requirements for new lead-free bearings.

In current process techniques to manufacture sliding bearings, bronze components are soldered to the respective parts, which is cost and energy intensive. Apart from that, so far most bearing materials still contain lead, which in new applications is omitted by EU law to avoid associated health risks. The present study aims to offer solutions for both by using cold gas spraying as additive manufacturing technique for processing bearings directly onto steel parts and by applying that to new lead-free bronze alloys. A lead-free bronze alloy was processed as powders by gas atomization and classified to optimum sizes for cold spraying. During cold spraying, the process gas pressures and temperatures as well as the substrate temperature were varied with the aim to study influences by impact conditions and effective surface temperature on particle deformation and bonding. Respective coatings show low porosity, high hardness and high electrical conductivities. With properties similar to that of bulk cast material respectively manufactured parts should meet the requirements for new bearing applications.

At present, main bearings in wind turbines are equipped with rolling bearings without exception. Sliding bearings instead can offer a number of advantages, including easier maintenance and extended lifetime. While conventional manufacturing processes for large sliding bearings face their limits regarding processable materials, thermal spraying can provide an effective alternative to meet the requirements by applying coating systems on the bearing surfaces. Within this study a wide range of different feedstock materials based on standard bearing materials and common wear and friction reducing coating systems are investigated. The coatings are tested on tribometers based on the load distribution within the main bearing at critical operating conditions of the wind turbine gained from a validated simulation model. A tribological methodology is developed to investigate the application related properties of the thermally sprayed coatings. The effects of load and geometry of the counter body on the friction and wear behavior of the coatings are investigated using a pin-on-disc and a modified high-load ring-on-disc tribometer. The presented results provide a major contribution to the purpose of identifying an appropriate coating system to meet the requirements of slow-moving and highly loaded sliding bearings.

High-Sn bearing alloys have been used for more than a century in many areas of industry. They are typically applied by casting, although thermal spraying is gaining in use, particularly for component repairs. This study evaluates the effects of HVOF spray parameters on the velocity, temperature, size, and trajectory of Babbitt particles and correlates the in-flight characteristics with coating porosity and intermetallic phase distribution. In the experiments, Babbitt layers up to 370 μm thick were deposited on carbon steel substrates while measuring particle properties and deposition efficiency. Coating samples were analyzed by means of optical and electronic microscopy and some were chemically etched to reveal the size and distribution of intermetallic phases. Test results show a significant refinement in intermetallic phase distribution when compared with commercial flame and arc-sprayed coatings.

This paper presents the results of metallographic investigations of electric arc sprayed composite coatings for the manufacture or refurbishment of bearing components. The materials studied include iron aluminide and aluminum bronze, and their interface microstructure was examined by optical and environmental scanning electron microscopy (ESEM).

New requirements for modern component part surfaces increasingly demand improvements over friction coefficients in the sense of a reduction of friction losses. A substantial control factor in terms of lower friction and wear is the use of coating solutions such as thermal spray coatings. In practice, the application of coatings by means of thermal spray is more and more often used for influencing tribological matching. However, surface microstructuring might represent an additional, further reaching solution for wear and friction behaviour improvements of tribologically high-stressed surfaces. The aim of the reported research project is the development of atmospheric plasma sprayed (APS) coatings with an inherent porous microstructure and surfaces with stochastically distributed nap volumes (from cut pores) regarding lubricant retention and -distribution in running surfaces of friction-type bearings. Subject of these investigations are in particular thermomechanically highly loaded hydrodynamic tribological matchings, amongst others by the example of a piston ring/cylinder system in engine blocks. The use of special fractioned Fe-base powders enables the production of a new type of coatings with an inherent porous microstructure, which offer advantages due to constantly regenerating their surface topology under wear, and maintain employment in tribological systems with increased loads due to optimized lubricant retention and distribution. Hence, this project has an emphasis on the design of optimal nap sizes in coating surface structure in dependence on the hydrodynamical load, as well as on investigations for the controllability of nap volumes by the design of suitable processes.

Al-Sn plain bearings for automotive applications traditionally comprise a multilayer structure. Conventionally, bearing manufacturing involves casting the Al-Sn alloy and roll¬bonding to a steel backing strip. Recently, high velocity oxy- fuel thermal spraying has been employed as a novel alternative manufacturing route. The present project extends previous work on ternary Al-Sn- Cu alloys to quaternary systems, which contain specific additions for potentially enhanced properties. Two alloys were studied in detail, namely Al-20wt.%Sn-lwt.%Cu-2wt.%Ni and Al-20wt.%Sn-lwt.%Cu-7wt.%Si. This paper will describe the microstructural evolution of these alloys following HVOF spraying onto steel substrates and subsequent heat treatment. Microstructures of powders and coatings were investigated by scanning electron microscopy and phases identified by X-ray diffraction. Coating microhardnesses were determined in both as-sprayed and heat treated conditions and differences related to the microstructures which developed. Finally, the wear behaviour of the sprayed and heat treated coatings in hot engine oil was measured using an industry standard test and compared with that of conventionally manufactured Al-Sn bearings.

A reduction of the size and weight of connecting rods can be obtained using the deposition of bearing materials by thermal spraying directly on the substrate. For this application several thermal spray processes are coming in competition. However the aspect of the metallurgical reactions during the coating deposition should be taken in count. The alternative of different technologies is presented with respect on the coating characteristics, the potential of industrialization and of the costs. The characteristics of the coatings are also strongly depending of the part geometry.

Wear and friction properties of aluminium titanate, zirconium silicate and magnesium zirconate atmospheric plasma sprayed ceramic (APS) coatings in contact with 100Cr6 steel were investigated under dry sliding conditions as a function of high temperature. The tribological tests were performed at different temperatures varying from 20 °C up to 800 °C using an High Temperature Ball on Disk Tribometer. The wear scar diameters of the 100Cr6 steel ball were measured by optical micrograph. The cross sections of the worn ceramic coated disks were determined with a Laser Profilometer. Results show that as a result of the higher temperature (up to 400 °C), the material yields more readily (softening effects ) and so adhesion is the dominant wear mechanism. For hybrid bearing, operating temperature of about of 200 °C must therefore be avoided.

Aluminium-based plain bearings for gasoline internal combustion engines are traditionally manufactured by casting and rolling, followed by forming and boring. The application places severe demands on the bearing material and a combination of properties such as fatigue, seizure and wear resistance are required. These properties are achieved by using a multi-phase material comprising of a distribution of tin in an aluminium alloy matrix. HVOF has been investigated as an alternative process for bearing manufacture and as a route to producing novel bearing materials with microstructures that cannot be achieved using the conventional casting route. The work reported describes the use of different HVOF spraying systems and powder types to develop aluminium-tin based coatings for advanced bearing applications. The coatings are described in terms of microstructure characteristics. The fatigue performance of the advanced sprayed bearings is compared with conventional cast bearings.

In the present paper rheological behavior of the Oxide Aluminum-Polymer Composite Sliding Bearing was examined. The requirements to the rheological models were formulated regarding adequate strain-strain state of the bearing. Rheological models of the composite sliding bearing have been proposed and were confirmed by in-situ experiments using principal Hertzian theory as the background. Load rating tests have revealed ultimate stresses of the sliding bearing and the strain-deformation modes of the sliding bearing ’ elements. The Oxide Aluminum-Polymer Composite Sliding Bearing was presented in the form of the complex elastic-tenacious-plastic rheological model. The metal-polymer layer was modeled by the rheological model consisted from two elastic elements and one tenacious element. As a prototype of the model, we studied a model comprising the Maxwells’ model and an elastic element. In general, a rheological equation depends on a level and form of strain applied. Analysis of the models and experimental results revealed better understanding of nanocomposite fracture and degradation mechanics. The nanocomposite exhibits linear relation of strain curve, whereas unloaded composite shows retardation of deformations (elastic return). The relations of experimental data and calculated data revealed very close agreement of developed rheological model and real mechanical behavior of the nanocomposite.

This paper compares the corrosion, friction, and wear properties of thermally sprayed aluminum bronze coatings developed for use on plain bearing surfaces. It explains how the coatings were produced, characterized, and optimized for the intended application. Paper text in German.

Quasicrystalline materials offer outstanding properties: High thermal stability in mechanical behaviour combined with special thermal and electrical conductivity as well as excellent tribological performance. High hardness is accompanied by heavy brittleness - an undesired property when looking for possible applications. A reduction of brittleness can be achieved by embedding quasicrystalline phases into a more ductile material to form a metal-matrix-composite material keeping some quasicrystalline properties. For thermal spraying blended, agglomerated, chemical encased or attrition milled powders as well as filled wires are processable to form such a metal-matrix-composite coating. The research work included spray trials using material-input prepared by the methods described. These different inputs have been processed in different compositions each. Spray trials have been processed by following techniques: Arc-wire-spraying, APS-spraying, wire-flame-spraying and HVOF-spraying. This paper gives an overview about HVOF-sprayed coatings with blended powders. On the one hand investigation were focused on metallurgical analysis for proving the existence of quasicrystal contents as well as determining adherence and embedding behaviour of the matrix-phase. On the other hand tests were centred onto the evaluation of the sliding-wear-behaviour in respect of interdependencies to the coatings composition and microstructure.

The full potential of rolling element bearings operating in specialised conditions such as high speed and corrosive environments are realised using surface coatings. Tungsten Carbide coating by thermal spray HVOF and D-Gim processes are considered for these applications. An experimental approach using a modified four-ball machine simulates the tribological conditions within a rolling element bearing. The fatigue failure modes of the tungsten carbide coating in rolling contact with steel and silicon nitride are examined using conventional surface analysis techniques. The stress fields within the coating are examined using traditional contact theory and residual stress measurement by X-ray diffraction. The residual stress measurements of the pre-test coating, the contacting surface and the fatigue failures are described. Results of residual stress relating to orientation, failure depth, coating thickness are discussed along with the fatigue failure mode.