Recently, environmental concerns have initiated intensive research and development in the field of friction brake systems with the aim to minimize particle emission. First brake systems that include thermally sprayed protective coatings on grey cast iron brake disks have been introduced in automotive industries and have proven suitability to strongly reduce particle emission. However, there is desire to use materials that show better environmental compatibility and lower price and to use processes that permit improved characteristics of protective coatings at reduced production costs. Different approaches concerning choice of base and coating materials as well as production processes are discussed with respect to technological, economic and ecological aspects. Besides grey cast iron also aluminum alloys are considered as base materials. For coating production HVOF spraying and laser cladding offer specific advantages and recent progress concerning the expansion of their production rate limitations is presented. Finally, novel feedstock materials that show excellent compatibility with stainless steel or aluminum alloy matrices have been developed and applied for coating production.

This study assesses the applicability of high-speed laser cladding for producing iron-based alloy coatings, in particular, CrNi duplex steel, FeCrV, and FeCrNiB. Process parameters are optimized for 150 µm thick claddings on mild steel using different laser power levels, surface speeds, and preheating temperatures. Claddings are also produced on cylindrical substrates of different diameters to investigate dependency on component geometry. Duplex steel was found to be highly processable by high-speed laser cladding. In contrast, crack-free FeCrV claddings can only be produced on small diameter surfaces, and only with preheating, while FeCrNiB could not be applied at all without cracking.

The influence of process gas composition on characteristics of laser cladding processes is studied in detail at the example of a 60 HRC nickel based self fluxing alloy powder. Typically pure nitrogen, argon or helium are used as process gases in laser cladding processes. Besides mixtures of these gases also addition of hydrogen, carbon dioxide and oxygen are applied studying their influence on thermal emission, weld penetration depth and homogeneity, powder usage and crack formation. Use of identical composition of carrier gas and laser process gas is compared to use of different carrier and laser process gases. Oxygen addition increases thermal emission, but does not result in increased weld penetration depth or crack formation tendency. Thereby homogeneity of weld penetration is improved in comparison to use of pure argon. Also, maximum hardness of claddings is achieved when adding oxygen.

Different types of tungsten carbide materials (fused tungsten carbide, nickel clad fused tungsten carbide, macrocrystalline WC and sintered and crushed WC/Co) are used for laser dispersing of construction steel surfaces. Surface roughness analyses and metallographic evaluation of cross sections concerning efficiency of carbide embedding as well as crack formation tendency are carried out. Generally, all types of tested carbides permit production of rough surfaces with metallurgical bonding to the metallic matrix, but only use of nickel clad fused tungsten carbide permits to prevent crack formation. The effectiveness of silicon and silicon carbide for production of durable rough surfaces on aluminium alloys is investigated. Both silicon and silicon carbide qualify for production of rough surfaces by laser dispersing. While silicon carbide particles show higher hardness, use of silicon does not include danger of embrittlement due to formation of aluminium carbide.

Multi-electrode APS has proven significant advantages with regard to spray rates, deposit efficiency and component life time. So far, three-cathode and three-anode spray guns have been established successfully in several industrial sectors where high spray rates are mandatory. Based on the successful three-anode plasma spray gun DELTA, the five-anode APS gun PENTA was developed to further increase productivity. With its gross power of up to 125 kW it allows very high spray rates and thus significantly reduced coating times. This paper focusses on the development of high spray rate parameter settings for producing oxide ceramic coatings. All coatings will be investigated with regard to their microstructures. Furthermore, economical benefits of the five anode technology will be highlighted.

A conventional GTV K2 kerosene fuel HVOF spraying system has been modified with the aim to achieve process conditions comparable to cold gas spraying concerning the average particle velocities and surface temperatures in the spray distance. The employed measurements include the use of expansion nozzles that have been optimized for supersonic conditions up to a Mach number of 2.5 and the use of combustion chambers with reduced critical diameters that provide increased combustion chamber pressures up to 1600 kPa. Copper powders with different size fractions and oxygen content are sprayed with the novel HVOF technology. Coatings are analysed concerning their microstructure, oxygen content and electrical conductivity. In-flight particle velocities and surface temperatures are determined by the GTV NIR Sensor. Results are compared with those obtained for cold gas spraying using identical powders. The new HVOF technology permits the production of copper coatings that show similar levels of porosity, oxygen content and electrical conductivity like cold gas sprayed coatings. Also aluminium powder has been sprayed successfully with the novel technology. In-flight particle velocities can be almost as high as in modern cold gas spraying systems. Coatings are analysed and show a microstructure comparable to cold gas sprayed coatings.

Titanium exhibits very good corrosion resistance property because of the formation of very dense oxide coating. Especially the good corrosion against Cl- solution for titanium material makes it wide applications in sea industry. It is very difficult to deposit titanium coating under atmospheric condition due to the strong affinity with oxygen and nitrogen especially in high temperature plume. Except the expensive LPPS process, much attention has been paid to the newly developed cold spraying. Unfortunately the stringent requirement for the starting power and low production efficiency limit the application of the cold spraying. A modified HVOF process was developed by reducing the outlet diameter of chamber and by directly introducing water into chamber, therefore lower plume temperature and higher chamber pressure than conventional HVOF process can be achieved. Attempts to deposit Titanium coating were carried out, and immersion of Titanium coated A3 steel into artificial seawater was performed in order to evaluate the density of as-sprayed Titanium coating. The results showed that dense Titanium coating could be obtained after parameter optimization and very few corrosion spot was observed on the surface of Titanium coated A3 steel after immersion into artificial seawater for 120 h.

According to the present state of the art “in situ, real-time control systems” are absolutely necessary in modern applications within the field of Thermal Spray technology with regard to the quality and reproducibility of thermal spray coatings for a wide range of industrial applications. Compared with the already existing diagnostic systems and their algorithms which are developed on the basis of CCD cameras, an algorithm can be developed for in situ, real-time control systems, which possesses a by far closer physical approach for the determination of the particle characteristics due to the measurement principle. Thus, about 300 particles can be detected per millisecond as well as average particle velocities within the range of 30 - 1200 m/s and average particle surface temperatures between 700 - 3000 °C can be determined. A statistical distribution of approximately 3000 particles is considered for the computation of the online measured average particle velocities and surface temperatures. The accuracy of the measurement determines the use of an online process control during Thermal Spray processes.

A conventional GTV K2 kerosene fuel HVOF spraying system has been modified with the aim to expand the applicable range of process conditions in order to also cover the presently existing gap between conventional HVOF and cold gas spraying. Different measures have been applied in order to reduce heat transfer and increase momentum transfer to spray particles. Increase of momentum transfer results both in reduced particle temperature as a consequence of reduced dwell time in the hot flame area and high particle velocities. In detail expansion nozzles with conical shape that provide improved expansion of combustion gases, combustion chambers with reduced critical diameters that provide increased combustion chamber pressures and the injection of coolant media water and / or nitrogen into the combustion chamber are applied. The effect of modified spraying conditions on the process characteristics and coating properties have been studied for a variety of materials. Besides copper, titanium alloys and MCrAlYs also WC/Co(Cr) and Cr 3 C 2 /Ni20Cr have been sprayed and respective coatings have been analysed concerning their microstructure, gas content, microhardness and wear resistance. In particular a moderate increase of oxygen content in dense titanium alloy coatings compared to the powder feedstock from 0.41 to 0.59 wt.-% proves the high potential of the undertaken measures to expand the application field of HVOF spraying. Thereby existing systems only need relatively small modifications to achieve this expansion.

For deposition of protective coatings different coating techniques are available. Usually, detailed evaluation of various deposit types and materials is necessary for selection of the best suited coating for specific application fields and demands. Subject of this work are thermally sprayed functional coatings applied as wear (and corrosion) protective layers. Examination of different optimized thermal spray coatings, i.e. HVOF sprayed WC/Co(Cr) and Cr 3 C 2 /NiCr coatings, conventional flame sprayed and fused self fluxing alloy coatings reinforced by hardmetal and APS sprayed oxide Al 2 O 3 /TiO 2 and Cr 2 O 3 coatings, is done in comparison to thick hard chromium platings. Two abrasive wear tests featuring wear by lose abrasive particles are carried out. These impart dry wear conditions according to ASTM G65 (Rubber Wheel test) and wear by abrasive suspensions according to ASTM G75 (Miller test). The work also contains evaluation of newly developed HVOF torch components permitting increased combustion gas, and therefore also particle, velocities concerning the benefit in terms of coating properties. Exemplary evaluation of the new components influence on velocity and temperature of spray particles is carried out by comparative SprayWatch analyses. Both the influence on the coatings microstructure and the wear performance are studied. Coating microstructure is evaluated qualitatively by optical and scanning electron microscopy and the micro hardness HV0.3 is measured. Worn surfaces are studied by SEM in order to deduce wear mechanisms.

Different post treatment methods such as heat treatment, mechanical processing, sealing, etc. are known to be capable to improve microstructure and exploitation properties of thermal spray coatings. In this work a plasma electrolytic oxidation of aluminium coatings obtained by arc spraying on aluminium and carbon steel substrates is carried out. Microstructure and properties of oxidised layers formed on sprayed coating as well as on bulk material are investigated. Oxidation is performed in electrolyte containing KOH and liquid glass under different process parameters. It is shown that thick uniform oxidised layers can be formed on arc sprayed aluminium coatings as well as on solid material. Distribution of alloying elements and phase composition of obtained layers are investigated. A significant improvement of wear resistance of treated layers in two types of abrasive wear conditions is observed.

The combination of excellent mechanical, thermal and chemical properties of silicon carbide (SiC) and titanium carbide (TiC) has made these materials very attractive both for structural ceramics applications and for thermal sprayed coatings. To suppress oxidation and to avoid the formation of silicides during spraying of SiC-based composites, feedstock spray powders have been developed containing 32 wt.-% of an alumina-yttrium ceramic binder matrix. The spray powders are prepared by spray-drying and sintering (a&s). Also, TiC-based composite spray powders showing the same matrix material and content have been developed and produced. Thermal spray processing of the described powders by atmospheric plasma spraying (APS) using an F6 APS torch and high velocity oxygen fuel spraying (HVOF) with the Top Gun G acetylene torch is carried out. Both the produced coatings and feedstock powder are characterized by optical microscopy, X-ray diffractometry (XRD) and scanning electron microscopy (SEM) including energy dispersive X-ray analyses (EDXS).

Though wire flame spraying is a relatively old thermal spray process, modern equipment permits production of high quality coatings featuring outstanding homogeneity, high density and low roughness due to increased particle velocities as a result of increased combustion gas velocity. Typically spray particles are accelerated to velocities exceeding 250 m/s, if the wires are atomized adequately. In order to make a wide spectrum of coating materials available for wire flame spraying use of cored wires needs to be considered. A high speed camera is used to determine the particle velocity depending on process conditions for massive, grooved cored and tube cored AISI 316L wires. Thereby the influence of the wire design without simultaneous influence by the chemical composition is studied. Additionally nickel based carbide reinforced coatings are sprayed and characterized concerning their microstructure and properties in use.

Newly developed iron based hard alloy powders with high chromium and vanadium contents are used for coating production by means of HVOF and LPPS. Crack free and dense coatings with fairly homogeneous microstructure are possible for both spraying methods. XRD analyses of sprayed coatings prove phase compositions similar to those of the powder feedstock when using HVOF systems. In contrast LPPS coatings contain a large share of amorphous phase. Microhardness of LPPS and HVOF coatings is about 1,200 HV0.3 and 800 - 950 HV0.3 respectively. The higher microhardness of LPPS coatings is attributed to the presence of the amorphous phase. However, LPPS coatings are brittle and tend to crack under mechanical load. Wear resistance of coatings is determined by means of corundum grinding disk and ASTM G65 wear test. Corrosion behavior is characterized by means of salt fog test and electrochemical measurements. Cermet and stainless steel 316L coatings are used for comparative purposes in the investigations.

HVOF sprayed cermet coatings are used for wear protection in numerous application fields. Most feedstock powders can be processed successfully with different spraying guns but optimized parameters for high quality coating production cannot be transferred directly. Besides substrate temperature only particle velocity and temperature inflight and at impact on the substrate determine the resultant coating properties. Two typical HVOF powders, WC/Co 88/12 and Cr 3 C 2 /Ni20Cr 75/25, are sprayed using the kerosene fuel system GTV K2 and particle parameters are recorded just prior to impact on the substrate with the passive diagnostic tool Spray Watch. Detailed correlation of particle parameters and the coating properties porosity and micro hardness as well as deposition efficiency is worked out in order to deduce particle parameter ranges providing coatings with defined optimum properties. The transferability to another kerosene fuel HVOF spraying gun, Tafa JP5000, is tested. It is also shown that effects like wear of the nozzle can be detected by use of the Spray Watch. Secondary correlation of particle parameters and machine settings is carried out to build a base for straight forward closed-loop control of the HVOF spraying process applying process diagnostics

Detailed studies concerning influence of microstructural features on the resistance of different thermal spray coatings against dry abrasive wear (Taber Abraser test) and oscillating wear (ball on disk configuration) are carried out. Besides WC and Cr 3 C 2 based cermet coatings produced by a triple cathode APS system with axial powder feed and by HVOF systems using kerosene fuel also APS Cr 2 O 3 and Al 2 O 3 coatings are tested. At the example of WC/CoCr coatings the influence of carbide size and content, powder size fraction, powder manufacturing process and spraying process parameters is studied. For APS Al 2 O 3 investigations concerning the influence of powder feed rate and nozzle geometry of single cathode APS torch are imparted. Oscillating wear tests are performed using alumina and hardened steel balls as counter bodies. Coatings are characterized concerning phase composition and residual stress state by means of XRD. Additionally microstructure is evaluated by SEM investigations and micro hardness is measured. Guidelines for manufacturing of thermal spray coatings fitting the specific demands of the two applied wear conditions are deduced.

HVOF sprayed WC/Co(Cr) and Cr 3 C 2 /Ni20Cr composite coatings have gained high acceptance in many industrial applications for protection of components against wear. The achieved coatings have quite good corrosion resistance for use of chromium containing matrices. Present research in the field of PTA-Surfacing resulted in the development of high chromium and high vanadium containing iron based hard alloys with simultaneous improvement of abrasive wear and corrosion resistance. These properties of the PTA-Surfaced coatings were studied and it was found that the newly developed alloys have nearly same wear resistance and improved corrosion resistance compared to Co-based alloys reinforced with Fused Tungsten Carbides (FTC). One major advantage of high chromium and high vanadium containing iron based coatings is machinability by turning and milling processes. These features make it attractive to be used in thermal spraying. The absence of substrate melting in HVOF-spraying is advantageous, as the coatings preserve the properties of the alloy due to prevention of dilution with substrate material in contrast to PTA-Surfacing. High chromium and high vanadium containing iron based atomized powder was used for HVOF spraying and deposition efficiency was measured. The sprayed coatings were studied metallographically by optical microscopy, SEM, XRD and micro-hardness measurements. Later, abrasive wear and corrosion properties of the coatings are investigated.

Titanium grade 2 as well as steel 446 and 316L powders are applied for production of X-HVOF coatings on mild steel substrates. Deposition efficiency is determined by process parameters. Microstructural investigations are carried out by means of optical microscopy, SEM and XRD. In addition comparisons of oxygen and nitrogen content in titanium coatings and powder feedstock are drawn. Corrosion protection capability of produced coatings is studied by current density-potential measurements and by salt fog tests. Depending on the process parameters increase of oxygen and nitrogen content can be restricted to factor of 2 compared to the powder feedstock. Coatings showing nearly theoretical density in metallographical inspections are possible. In direct comparison to wrought titanium grade 2 material the corrosion behavior of the titanium coatings is very promising. Keeping in mind that coatings have been produced under atmospheric conditions the observed increase of the corrosion current density by factor four is regarded an excellent result. During the corrosion tests no damage, neither to the surface nor the substrate - indicated by rust precipitates on the specimen surface, is observed. So penetration of corrosive medium to the substrate is securely avoided.

Application of cold gas spraying for deposition of braze filler coatings is investigated. Different light weight alloy substrates, i.e. aluminum AA1050, AA3005, AA5754 and AA7022, magnesium AZ91 and titanium TiAl6V4, are used. Filler coating materials depend on the substrate melting temperature. So for aluminum alloys Al12Si and zinc based fillers, for AZ91 pure zinc and for Ti6Al4V different Cu-Ni blends are applied. CGS process parameters are varied with regard to process gas (nitrogen) temperature and pressure, powder feed rate and spray distance. Correlation to process characteristics and economical aspects are given. The usability of the produced filler coatings is shown by different optimized brazing/soldering processes. In case of aluminum braze joints a full metallographical investigation is carried out by optical and scanning electron microscopy as well as EDXS analyses. The gathered results are compared with those of conventional filler material addition, i.e. wire, roll plating and foil.

For constant conditions concerning substrate state, feedstock and environment properties of thermal spray coatings depend only on temperature and velocity of particles at impact on the substrate. Two different HVOF spraying guns, the kerosene fuel system Tafa JP5000 with radial powder injection and the ethylene fuel system Sulzer Metco Diamond Jet Hybrid 2700 with axial powder feeding, are characterized concerning the evolution of space resolved velocity and density of particles by LDA. Also influence of process parameter variations is examined. The region of shock diamonds is studied specifically. The influence of different characteristics concerning impact velocity and trajectories on the coatings microstructure is determined by means of optical microscopy and microhardness testing.