An important parameter that affects the protection from wear and tear, is the geometric structure of the abrasive causing the destruction. The equivalent diameter of the particles of the primary influence on protection from wear and tear must be greater than the width of the particle of the crushed abrasive. Here also belongs the requirement for the distribution of the particles inside the matrix was more uniform and dense. The use of solid materials gives this possibility only in the certain circumstances, therefore, it is necessary to use pseudoalloys. Pseudoalloys can be obtained by means of thermomechanical processing of the conventional layers deposited by means of spraying. The particles of the solid material charged with kinetic energy are applied to the heated layers, and they penetrate into inside. Under the influence of the heat energy inside the layers suitable for this, the additional reaction between the substrate and the layer takes place, thus improving the adhesion of the layers. The appropriate regulations were developed, and the reproducible stratification appeared caused by spraying, that is pseudoalloys. A positive consequence of the inclusion of the particles of a solid ceramic material into the spayed layer is the emergence of the current when compressed. The result of the research of the parameters are the optimal performance indexes, optimization criterion served as an indicator of the intensity of the wear. Manufactured pseudoalloys underwent checking in terms of spray wear. The study of spray wear was carried out at the temperatures up to 750 ° C and speed load amounted to 37.5 m/s. The silica sand fractions + 150-212 µm was used as an abrasive. As the covering material the alloys based on aluminum were used. In the places of transition to the substrate the multiphase alloys of the system Fe-Al are formed. It is advisable to use layers with a high iron content to prevent the loose and destruction.

This study evaluates the friction and wear behavior of iron-base coatings produced by arc spraying using experimental cored wires. Coating microstructure was analyzed and various wear tests were performed. The results show that the tribological properties of the ferrous coating materials are greatly affected by porosity, oxide inclusions, particle shape, and microhardness.

The aim of this work is to optimize molybdenum disilicide coatings for high-temperature oxidation protection of metallic surfaces. Agglomerated and sintered MoSi2 powder was deposited on test substrates by atmospheric plasma spraying. The powders and coatings were characterized by means of optical and scanning electron microscopy. Various tests were carried out to determine the influence of powder size and spray parameters on coating porosity, hardness, and adhesive pull strength.

Cermets like WC/Co or Cr 3 C 2 /Ni20Cr are well-established materials for thermally sprayed wear protection coatings. However, their high price and the adverse health effects of nickel and cobalt cause the motivation for the development of novel materials with excellent wear resistance. Within the AiF/DFG research cluster “Thermal Spraying”, a multi-institutional cooperation of various German research centres, the focus is put on particle-reinforced iron-based composite alloys. High-alloyed steels serve as matrix materials into which hard CrB 2 particles are incorporated by means of high-energy ball milling (HEM). By adjusting appropriate milling parameters, the microstructure of the powder and its level of amorphisation can be influenced effectively. The high-velocity oxygen fuel process (HVOF) allows a transfer of the desired nanocrystalline structure from the particles to the coatings. The deposited coatings exhibit low porosity and high microhardness values of more than 1000 HV0.3. The wear resistance of the coatings was determined by means of Miller test (ASTM G75-01) and compared with conventional wear protection materials and coatings produced with agglomerated and sintered powders. The obtained outstanding results qualify particle-reinforced iron-based materials as a promising alternative for a wide range of applications.

Several model Fe- and Ni-based alloys with increased content (up to 30 at.-%) of protecting scale forming elements were developed. High temperature corrosion resistance of bulk alloys as well as thermally sprayed coatings and welded overlays were investigated under the waste power plants simulated atmosphere (500 °C, 100 hours, 75N 2 -20O 2 -4.9Ar-0.1Cl 2 ). Arc and HVOF spraying as well as PTA overlay welding were used to produce the coatings. After an exposure the samples were examined with electron probe micro-analysis (EPMA). It was shown that the protection behaviour of overlay welds depends on the content of alloying elements, although the last is limited because of weldability decrease by high alloying level. High temperature corrosion resistance of thermally sprayed coatings is determined by their porosity, which can be varied over a very broad range depending on the applied spray method. The arc sprayed coatings need an additional post-treatment to close a porosity. Two methods were applied, pre-oxidation treatment in the air and sealing with the commercial sealant. Newly developed iron-based coatings with increased aluminium content (< 20 wt- %) sprayed with HVOF-spraying with powders obtained by means of high energy ball milling demonstrate high corrosion resistance. Selected coatings were evaluated for 1000 h exposure under chlorine-containing salt deposits at the higher temperature (600 °C).

Solid-particle erosion of metals and alloys at elevated temperatures is one of the main reasons of the damage of components used in the energy production and utilization industries. Application of protective coating systems can be an attractive and economically reasonable solution for preventing the failure and increasing the durability of the components working in severe conditions of high-temperature corrosion and erosion. However, thermal spraying of intermetallic materials that have excellent high-temperature corrosion resistance is limited because of their low ductility. Present work reports the results of the investigation of abrasion wear resistance at elevated temperatures of combined coatings, which include the intermetallic layer. Such iron aluminide layers have been formed as a result of diffusion during the heat post-treatment of arc-prayed metallic coatings combining Fe- and Al-based layers. Post-treatment of arc-sprayed coatings was carried out by means of infrared radiation and induction heating. It was shown that the abrasion resistance of the developed coating tested at elevated temperatures (T > 500 °C) is considerably higher than that of low-alloyed steel and some nickel-based alloys and depends on the test load condition. The high performance of intermetallic-based graded coatings at elevated temperatures makes them interesting for applications as a low-cost erosion-corrosion-resistant material.

Thermally sprayed alumina coatings are widely used in a range of industrial applications to improve wear and erosion resistance, corrosion protection and thermal insulation of metallic surfaces. These properties are required for many components for production processes in the paper and printing industry. By means of efficient and adjustable coating processes, long-term use of the refined surfaces is obtained. It can be seen that cost-efficient arc-sprayed Al coatings post-treated by plasma-electrolytic oxidation (PEO) form Al 2 O 3 -layers with outstanding hardness, bonding strength, abrasion and corrosion resistance as well as extended service time. These coatings are designed to partially replace hard chromium.

The thermal spray application of inert gas atomised iron based powders for combined wear and corrosion protection prospectively offers important economical advantages compared to the well-established cermet coatings due to their lower price. Recent studies revealed basic knowledge about the thermal spray processing of these materials. For protecting the substrate from corrosive media, coatings have to be dense and impermeable to fluids. Especially poor bonding, occurring between partially melted or unmelted spray particles, leads to open porosity. Hence a certain degree of melting of particles is required. The GTV K2 spray gun allows the use of different nozzles to vary process temperature and velocity in a wide range. This paper shows the influence of applicated nozzles and process conditions on coating characteristics. Powder and coating characterisation is carried out by means of optical microscopy, digital image analysis, SEM and XRD. Additionally, some results regarding microhardness and wear behaviour are given.

Development of new arc sprayed iron based coatings for protection against gas abrasive wear at room and elevated temperatures are of the great interest because of permanently increasing pressure to reduce production and repair costs of power production facilities. Two cored wires in steel cover with Fe-Cr-B-Al and Fe-Cr-N-Al filling are proposed as an alternative choice for self fluxing and cermet coatings that are considered nowadays for protection of screen tubes of boilers of power stations that are operated under the temperatures 500-600 °C. Oxidation behaviour of arc sprayed coatings is estimated by gravimetric measurements. Abrasive wear resistance at elevated temperatures after 1 hour is investigated by means of laboratory unit that alloys a rotation of coated specimens in heated quartz sand. It is shown that abrasion wear lost of carbon steel increases 1.5 times when test temperature increases from 20 °C to 550 °C. For all investigated coatings the 20-25% decrease of wear lost is observed at higher temperature. Arc sprayed coatings of both investigated systems improve significally the abrasive wear resistance of carbon steel. At room temperature the improvement by factor 1.3-2.2 times and at the temperature 550 °C by factor 2.7-4.6 is observed depending on chemical composition of coatings.

Different post treatment methods are developed up to now to improve the properties of thermally sprayed coatings. In this work, arc sprayed aluminium coatings on aluminium substrates are post-treated by plasma electrolytic oxidation. To estimate the wear resistance of resulting oxide coatings, two abrasive wear tests (ASTM G65 and ASTM C1624) are carried out. Worn surfaces are examined by scanning electron microscopy in order to establish the wear mechanisms. These results of the abrasive wear tests are correlated with the parameters of the PEO process and the hence resulting micro structures of the coatings.

The implementation of magnesium alloys for automotive, aeronautic and other applications is of the great importance due to their especial properties. Magnesium offers greater weight saving capacity than aluminium, as its density, 1.7 g/cm -3 , is two thirds the density of aluminium, 2.7 g/cm -3 , without significant loss of strength and magnesium alloys show high specific strength. On the other hand surface properties of magnesium alloys like wear and corrosion resistance are rather poor. A large amount of methods are intensively elaborated to overcome this problem from developing of new alloys, different surface treatment methods and a great variety of coating systems. In present work the results concerning improvement of corrosion and wear resistance of magnesium alloys by means of zinc based coatings are presented. Coatings are deposited on magnesium substrates (AM20, AZ31, AZ91) by arc spraying with Zn, ZnAl4 and ZnAl15 solid wires as well as by electroplating of zinc. Nevertheless the onset of bimetallic corrosion between Zn and Mg significantly increases corrosion current density. In order to provide longer protection, two main technological solutions are taken into consideration. First relies upon a modification of the main electroplating technology, second is based on the selection of an effective post treatment. For the first approach a consecutive process is elaborated based on the two-step electrodeposition. The first is from alkaline bath followed by the second step in acidic chloride bath. A dense and compact complex layer is obtained. The second approach is based on the post treatment of deposited coatings and provides a formation of thick and uniform reaction layer in magnesium on the interface between zinc or zinc based coating and substrate. These layers have fine eutectic structure with microhardness 3-4 times higher than that of the base material. Heat treatment is carried out with focused irradiation of tungsten halogen lamp line heater in atmosphere. Microstructure of deposited coatings as well as that of modified surface layers is investigated by metallographic methods. Corrosion properties are estimated by electrochemical measurements. Abrasion wear resistance of the modified layers is determined by scratch test and oscillating wear tests. It is shown that the both applied methods improve corrosion properties of magnesium alloys. Electrolytic zinc coatings deposited by electroplating in the elaborated two- step process demonstrate good barrier properties. Durability increases about three times in comparison with a single coat obtained from alkaline bath. Infra red heat treatment of thermal spray coatings results in formation of modified layers in magnesium substrates that prevent the galvanic corrosion of investigated systems. Wear resistance of reaction layers is up to 4 times higher to compare with the base material.

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.

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.

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.

This paper presents the results of a study on arc-sprayed coatings made from powder-cored wire. The wires used consist of a ferrochromium core with additions of boron, aluminum, and carbon compacted in a steel sheath. The coatings are sprayed using a modified burner operated at 34 V and 140 A with an air jet pressure of 0.6 MPa. During spraying, specimens are rotated at a speed of 60 rpm. XRD analysis is used to examine the initial phase composition of the layers as well as friction-induced changes in the subsurface resulting from block-on-ring wear tests. Cross-sectional examination shows that the coatings have low porosity (∼10%) and small grain size (50 to 150 µm). Based on these findings, it is concluded that the wear resistance of wire arc sprayed coatings is largely determined by powder wire composition, initial coating structure, and the structural stability of the subsurface layer. Paper includes a German-language abstract.

This paper investigates the adhesion of thermally sprayed ceramic particles on metal substrates. Two aluminum oxide powders are applied to nickel-oxide coated steel substrates by detonation and vacuum plasma spraying. SEM and XRD fracture analysis is used to examine the ceramic-metal interface and the morphology of fracture surfaces. In all test samples, failure occurs in the alumina, not at the interlayer boundary, indicating a high level of adhesion between the ceramic and nickel oxide layers. Paper includes a German-language abstract.

This paper investigates the effect of laser treatment on alumina-TiO 2 coatings deposited by detonation spraying. It describes the changes observed in the microstructure and hardness of the remelted layers. The originally lamellar structure is transformed into a fine, pore-free columnar structure in which the grains are oriented perpendicular to the interface between the layer and substrate. The remelted zones contain alpha-aluminum oxide as the main phase and are characterized by high microhardness, although a few defects were observed on the periphery. Paper includes a German-language abstract.