Aluminum titanate (Al 2 TiO 5 ) is a congruently melting compound in the binary Al 2 O 3 -TiO 2 system, which decomposes below 1200 °C. Its properties (e.g. thermal conductivity, CTE) differ significantly from those of Al 2 O 3 and TiO 2 . Thus it is of special interest to study the stability of Al 2 TiO 5 in the spray process and its influence on the coating properties. A commercial fused and crushed Al 2 O 3 -40%TiO 2 powder, which was found to be substoichiometric, was selected as the feedstock material for the experimental work, as the composition is close to stoichiometric Al 2 TiO 5 . Part of that powder was heat-treated in air at 1150° and 1500°C in order to vary the phase composition, while not influencing the particle size distribution and processability. The powders were analyzed by thermal analysis, XRD and FESEM including metallographically prepared cross sections. A powder having Al 2 TiO 5 as the main phase was not possible to be prepared due to inhomogeneous distribution of Al and Ti in the original powder. Plasma spraying was performed with a TriplexPro-210 (Oerlikon Metco) using Ar-H 2 and Ar-He plasma gas mixtures with 41 and 48 kW plasma power. Coatings were studied by XRD, SEM of metallographically prepared cross sections, and microhardness HV1. Moreover, the results show a clear influence of the Al 2 TiO 5 content in the feedstock powder on the phase composition of the coatings.

The wear of piston rings in large marine two-stroke diesel engines is a major maintenance cost. Applying coatings with good oxidation, corrosion resistance and high temperature strength, can lower the total maintenance cost. In the past nickel aluminide with chromium carbide have been applied to pistons by thermal spraying. Using laser cladding a suitable microstructure can be formed while at the same time avoiding cracks and bonding issues. In this report powders and coatings were manufactured in order to be able to investigate the dry-sliding wear behavior. Material with three levels of carbides was atomized. Wear test samples were manufactured by laser cladding. The dry sliding wear-mechanism maps are generated by using block on ring test setup where coated blocks slide against cast iron rings. All alloys exhibited regions of plasticity-dominated wear and oxidational wear with a transition region in-between. The carbide-containing alloys showed lower friction and wear in comparison to the carbide free nickel aluminide alloy.

Next to ZrO 2 , compositions in the system Cr 2 O 3 -TiO 2 -Al 2 O 3 are the most used ceramic materials for thermally sprayed coating solutions. Cr 2 O 3 coatings present good sliding wear resistance, Al 2 O 3 coatings show excellent insulation behaviour and TiO 2 striking corrosion properties. In order to combine these properties, coatings containing more than one oxide are highly interesting. The conventional spraying process is limited to the availability of binary feedstock powders with defined compositions. The use of suspensions offers the opportunity for tailor-made compositions: within the triangle of Cr 2 O 3 -TiO 2 -Al 2 O 3 each mixture of oxides can be created. The formulation of binary or ternary suspensions is based on the preparation of stable single-oxide suspensions, which will later be mixed to achieve the desired composition. This procedure requires the development of water-based suspensions with suitable behavior, otherwise the ceramic particles and dissolved organic additives may interact and form agglomerates, which are prejudicial to the thermal spray process. This work presents criteria for the selection of raw materials as well as relevant aspects for the development of binary suspensions to be used in thermal spray. For procedure validation, coatings sprayed using Cr 2 O 3 -TiO 2 suspensions and S-HVOF will be shortly presented and analysed in terms of their microstructure and microhardness.

Yttria-Stabilized Zirconia (YSZ) suspensions are currently popular in developing strain resistant columnar structured thermal barrier coatings by Suspension Plasma Spray (SPS) as a less costly alternative to conventional EB-PVD. Coatings produced by SPS have a disadvantage of reduced usable spray distance, compared to conventional APS, due to quenching of the plasma by the suspension liquids, which are most commonly alcohol-based. The reduced spray distance can interfere with the coating process for substrates with complex geometries such as turbine blades. This paper shows how spray distance can be increased by using larger suspension particle sizes that are not normally considered for SPS. Such large particle suspensions are shown capable of producing columnar or segmented YSZ coating microstructures that are similar to those produced by submicron particle suspensions, but at longer and more practical spray distances. Another limitation to SPS process technology is the delivery system of feedstock from the point of manufacture to the SPS feed hopper. Current commercial ready-to-use suspensions have limitations involving cost, transportation and storage that effect both the producers and the end-users. An alternative suspension delivery system may be applied to SPS feedstock materials, including current sub-micron and the coarser particle size cuts described herein. Discussed is a pre-formulated dry feedstock that is constituted into fresh suspension by the end-user with locally sourced liquid media and appropriate high-speed mixing equipment. This alternative delivery system for suspensions provides lower cost materials and process flexibility that is particularly suited to commercial scale SPS coating facilities.

The currently available powders are for conventional high power HVOF or APS. There is an increasing need for low-power HVOF and HV-APS torches for coating temperature-critical parts and inner diameters. Using them for the new applications causes massive restrictions such as poor coating efficiency, much overspray, rough surface or defects in the layer structure. However, just using ultrafine powders does not solve the problem. The disadvantages in terms of fluidity and oxidation resistance need to be solved, too. Beside the development of modern HVOF, ID-HVOF and Three-cathode-APS coating systems Thermico pursues a continuous enhancement of customized powders. Due to this steady development, Thermico has realized spraying inner diameters with just 10 – 20 mm stand off by using a new WC carbide powder which is able to absorb enough energy out of the low power flame to build up a very dense high quality coating. The modified WC Co 83 17 powder is available for ID HVOF. The high quality coating of outer diameters with a HV-APS is another solution which Thermico has successfully developed. Beside this Thermico had the goal to establish a high quality HV-APS coating to prices competitive to HVOF.

Tungsten carbide -based hard metal coatings are extensively used in demanding industrial applications like for wear protection purposes. Continuously increasing demands set new limits and need for materials with enhanced features. One solution is to improve hard metal properties by nanostructures. Presented study is part of a research where novel and safe route to manufacture nanostructural WC-Co powders starting from water soluble raw materials was developed. In this study powders’ workability in thermal sprayings is studied. WC-12Co powder was manufactured using water soluble raw materials: ammonium metatungstate as a tungsten source, glycine as a carbon source and cobalt acetate as a cobalt source. The powder was manufactured via optimized spray drying and heat treatment method producing a correct phase structure and chemical composition. Experimental powder was sprayed by HVAF-spraying to study its workability and functionality. Morphology, microstructure and properties were analyzed from the experimental nanostructural powder and the HVAF-coatings.

This paper summarizes the results of a decade-long study on nanoparticle reconstitution and its role in thermal spraying. The effect of the reconstitution process on coating nanostructure was investigated for different materials and applications, a number of which are covered in this report, including Al 2 O 3 -TiO 2 , SiC-Al 2 O 3 -ZrO 2 , and zirconia-based TBCs.

In the present study, a new multi-chamber detonation sprayer (MCDS) was used to deposit Al 2 O 3 coatings on titanium and carbo steel substrates. SEM, TEM, and XRD analysis of the layer between the coating and substrate revealed the presence of an intermetallic compound that improves coating properties and is conducive to the relaxation of stresses generated during spraying.

In this study, WC-Co coatings with nano-sized TiC additions were deposited on steel substrates by high velocity air fuel (HVAF) spraying and their microstructure and phase composition was analyzed using different electron microscopy techniques. Tungsten-reinforced cobalt phases detected in the vicinity of WC grains were identified as Co 0.9 W 0.1 by selected area diffraction. No titanium phases other than TiC were found, which suggests that nano-TiC may increase the stability of metallic matrix microstructure in WC-based coatings.

This study investigates the formation of ZnNi/Cr 2 O 3 -TiO 2 -CuO-SiO 2 /PTFE composite ceramic coatings by atmospheric plasma spraying and assesses their ability to improve the corrosion, friction, and wear performance of reciprocating parts. The as-sprayed coatings were examined then subjected to a series of tests to evaluate corrosion and fouling resistance. Reciprocating parts that had been coated were relatively intact after 5000 h in a realistic ocean environment. Cyclical changes in coating weights were found to be influenced by the dissolution of oxide films and the accumulation of secondary products. PTFE proved to be an effective sealing agent, reducing mass loss and porosity by approximately 30%.

This study assesses the viability of producing electrically conductive carbon nanofiber (CNF) reinforced mullite coatings by thermal spraying. Mullite-CNF agglomerated powder was prepared by spray drying and was deposited on steel by atmospheric plasma spraying. The coatings obtained are characterized based on composition, structure, shape, thickness, and electrical conductivity and are compared with coatings produced from commercial mullite powder.

Thermal spray coatings produced from suspensions can be precisely tuned in terms of thickness, surface morphology, microstructure, and properties. This paper discusses the benefits of using suspensions as feedstocks for atmospheric plasma and HVOF spraying, the equipment required, and the technological challenges that remain to be solved.

This paper presents a method for producing TiC-NiCr cermet powders with particle sizes of 40-90 μm and 15-50% volume content of ultrafine carbide inclusions. The method is based on a combination of mechanoactivation of initial components and subsequent high-temperature self-propagating synthesis. TiC-NiCr powders with different amounts of carbide content were produced and their applicability for plasma spraying is assessed.

The present study describes the development of agglomerated and sintered WC and Cr 3 C 2 based cermet powders with complex and highly corrosion resistant Fe and Ni matrix alloys. In addition a Fe-Cr-C with a Ni matrix was tested as a potential low cost alternative to standard Cr 3 C 2 -NiCr powders. The powders were sprayed by HVOF using liquid and gaseous fuel. Microstructure and phase composition of the coatings were analyzed by microscopy and X-ray diffraction. The technical properties of the coatings were examined by hardness measurements, abrasive wear and cavitation tests as well as corrosion tests. The results were compared with state-of-the-art coatings of WC-Co-Cr 86/10/4 and Cr 3 C 2 -NiCr 75/25.

Traditional fused and crushed (F&C) titania feedstock powders have relatively poor flow and are limited in the feed-rates that can be achieved before deposition efficiencies (DEs) start to decline. In addition, the coatings made with F&C powders generally have high stiffness and limited fracture toughness. Such coatings bear the risk of cracking/delaminating particularly in the case of thick coatings. To address these issues, a new agglomerated and sintered (A&S) titania feedstock powder has been developed and compared in side-by-side spray tests to the traditional F&C titania powder of comparable particle size. The spray behavior, achievable feed-rates and DEs, as well as the resulting coating characteristics were evaluated from the view point of their application as thick, electrically conductive coatings. The new A&S powder yields up to approximately 200% improvement in DE while producing coatings with more suitable microstructure, lower electrical resistivity and higher thickness. Furthermore, for a given set of process parameters, the DEs obtained with this new powder show little sensitivity to the powder feed-rates, thus allowing spraying at higher feed-rates without compromising coating DEs. This feature of the powder has significant commercial advantages for thick coatings when combined with high throughput guns such as TriplexPro-200. Preliminary results of particle diagnostics towards understanding of the fundamental principles behind these improvements are also discussed.

Thermally sprayed cermet powder coatings as well as bulk cermet materials sintered of carbide/metal powder blends are widely used in applications with severe abrasive wear conditions. A cost-saving alternative can be provided by using iron-based melt-atomised hard alloy powder feedstocks. Among them, commercial alloys containing high amounts of vanadium and carbon obtain outstanding wear resistance due to their high volume fraction of finely dispersed, hard vanadium carbides. However, their performance is still exceeded by cemented carbides. A further improvement of the wear properties of hard alloys basically can be attained by increasing their carbide content, concurrently considering the limitations of the melting and atomisation process regarding the melting temperature. A possible solution can be provided by alloying the basic system Fe-V-C with an additional strong carbide former like niobium. Subject of this work is the comparing investigation of the technologically important melting equilibria in the systems Fe-V-C and Fe-V-C-Nb.