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.

This study investigates the phase stability and thermophysical properties of Y 2 O 3 and Yb 2 O 3 co-doped SrHfO 3 (SHYY) powder and bulk material along with the phase stability and microstructure evolution of as-sprayed SHYY coatings during annealing. The powder was synthesized by a solid-state reaction at 1450 °C, showing good phase stability up to 1400 °C. Dilatometry measurements revealed no abnormal changes in the coefficient of thermal expansion over a temperature range of 200-1300 °C. The thermal conductivity of the bulk material was found to be 16% lower than that of SrHfO 3 . Free-standing SHYY coatings deposited by air plasma spraying were also tested. The coatings consisted of SHYY and a minor amount of secondary phase Yb 2 O 3 and exhibited good phase stability during heat treatment at 1400 °C for 288 h. Coating samples examined after 216 h still exhibited a columnar microstructure.

NiAl-Al 2 O 3 intermetallics based composite coatings were prepared by cold spraying of Ni/Al-Al 2 O 3 composite powders followed by post-spraying annealing treatment. The phase transformation mechanism from Ni/Al mechanical alloy to intermetallics was explored to aim at controlling the microstructure of the composite coating. Results showed that, with the porous Ni/Al and Ni/Al-Al 2 O 3 green compacts, self-propagating high-temperature synthesis (SHS) reaction was ignited at a temperature of 500-600°C. However, SHS reaction was not able to be ignited for the cold-sprayed dense Ni/Al alloy coating with or without substrate. SHS reaction was even not ignited for the Ni/Al-40vol.%Al 2 O 3 composite coating, although the thermal conductivity of the coating was significantly decreased by the addition of Al 2 O 3 ceramic particles. The phase transformation from Ni/Al mechanical alloy to NiAl intermetallics during post-spraying annealing can be evidently attributed to diffusion mechanism.

With the purpose of elaborating high-quality FeAl coatings, a so-called very low pressure reactive plasma spray technique that combines VLPPS and SHS processes was used in the present study. A dense and homogeneous FeAl coating was thus successfully in situ synthesized by reactive plasma spraying of an Al/Fe 2 O 3 composite powder under 1 mbar. The phase composition and microstructural features of the coating were characterized by XRD and SEM. Results indicated that the B2 ordered FeAl phase was synthesized, and the coating featured a dense and defect-free microstructure. The fracture mechanism of the coating remains mainly a brittle failure but the appearance of some dimples in local zones suggests some unexpected toughness.

This paper reviews various powder treatments and particle alteration processes and evaluates their effect on the microstructure and properties of thermal spray coatings. It discusses the benefits and drawbacks of thermal plasma treatments for powders, the use of self-propagating high-temperature synthesis (SHS), and different ways nanopowders are produced and sprayed. It covers several spraying methods and a wide range of materials, including ceramics, metals and alloys, cermets, and composites. It also covers mechanical alloying and powder milling processes and addresses the potential risks of inhaling nanopowders.

Known methods of production of composite powders have a series of deficiencies. The method of self-propagating high-temperature synthesis which has appeared recently has conclusive advantages. The method allows forming in a single work cycle micro and a macrostructure of a composite particle. The present work is devoted to viewing of questions targeted mechanical activated synthesis of composite powders for thermal spraying of function coating of various applications. Results of synthesis of powders Ti and Cr carbides in oxygen atmosphere are given.

Presently, the self-propagating high-temperature synthesis (SHS) has found wide use in the production of compacts and powder materials, and also in the fabrication of end products. Yet, a disadvantageous feature of the standard SHS process, which can be overcome in part by running the synthesis reaction under pressure, is that it fails to provide the possibility of obtaining high-density materials and products. It is therefore of interest to develop a combined process which would allow one to apply a two-component Ni-Al coating with prescribed stoichiometric composition by cold spraying of a nickel-aluminum powder mixture followed by self-propagating high-temperature synthesis of a target intermetallide (Ni3Al or NiAl) by treating the surface layer of the cold sprayed coating with a highly-concentrated energy flux (argon plasma jet). Preparation methods for nickel-aluminum powder mixtures (in particular, mechanochemical activation) intended for cold spraying process are discussed. Computational experiments were performed to substantiate the choice of stationary, traveling and pulsed energy sources for subsequent initiation of SHS in the heterogeneous layer deposited onto a steel substrate. A model was developed to predict the local phase state of the material synthesized in the coating; this model involves the state diagram of the Ni-Al system. The characteristics of sprayed coatings were examined. The developed approach is shown to offer much potential in practical applications.

An important growth potential in thermal spraying industry consists of the development of new coating materials. Metal- or Ceramic-Matrix-Composites (MMC / CMC) are of special interest due to a variety of properties which can be influenced particularly by the ratio of matrix and reinforcing material. Thermal sprayed coating properties mainly depend on thermal and kinetic energy of the spray particles. An increase in thermal energy of sprayed particles can be obtained by Self Propagating High Temperature Synthesis (SHS) reaction between components of the spray material. Hence a higher adhesive strength, a lower porosity and an increased deposition efficiency can be expected. Aluminium-based spray materials, containing metal oxides, are suitable for the Self Propagating High Temperature Synthesis to produce MMC-coatings. For good contact between the reactants, powders of aluminium and chromium oxide for plasma spraying were prepared by mechanical alloying. Coatings characterization results on the base of optical microscopy, scanning electron microscopy (SEM), X-ray structure analysis (XRD) and measurements of velocity and temperature with a DPV2000 system. The plasma spraying process combined with SHS reaction of the spray material leads to raised enthalpy of spray particles combined with an increased ad-/cohesive strength and a lower porosity as well as an increased deposition efficiency.

Obtaining dense ceramic coatings by thermal spraying still remains a challenge. Compared to metals, ceramics have a lower thermal conductivity and a larger melting enthalpy. These factors limit the heat transfer from the plasma to the particles and consequently do not necessarily allow their total melting. Problems linked to this heat transfer can be avoided, or at least limited, by using agglomerated particles made of a mixture of reactive powders yielding the ceramic material, via SHS (Self-propagating High-temperature Synthesis) reaction. In this case, the reaction can be ignited by the heat transfer at the particle surface of an agglomerate and propagate towards the centre during its flight through the plasma. The application of this process to Ti, C mixtures leads to the formation of a dense TiC based coating. The composition of the coating, influenced by the contamination of the surrounding gas entrainment during the spray process, belongs to the TiC-TiO solid solution. The influence of experimental parameters on the coating composition is discussed.

This work reports research concerning the production of powder, suitable for reactive HVOF spraying, produced by mechanically alloying Ni(Cr), Ti and C elemental powder constituents. Powder mixing was achieved using a high-energy Uni-Ball II Mill and optimisation of the milling parameters are reported. The composition of the powder, at 50wt.%NiCr-40wt.%Ti-10wt.%C, was such that the application of heat has the potential to cause a SHS (Self propagating High Temperature Synthesis) reaction to take place. The utilisation of SHS reactions to produce TiC particles within metallic matrices is well known in bulk systems. However, this work describes carrying out this reaction in individual powder particles on exposure to the high temperature within the HVOF gun. The powder having undergone the SHS reaction during the spray process was deposited onto mild steel substrates to form a dense, coherent coating. The coatings thus formed were shown to contain nanoscale TiC in a Ni(Cr) matrix, indicating a SHS reaction had taken place. This TiC is much finer than that produced in conventional SHS reactions, which is typically ~5ìm. The percentage of TiC formed, and retained in the coating, was lower than expected from the constituent proportions and explanations for this observation are proposed. The microstructure of the coating is described and compared with a Ni(Cr)-TiC cermet coating sprayed using conventional SHS powder generated from reacted compacts which were crushed, sieved and classified to give sprayable feedstock powder.

The aim of this work is to determine how to control the microstructure and tribological properties of HVOF-sprayed TiC composite coatings. The powders used in the study were made by the SHS process and contained a mixture of TiC and either FeCr20Ni10 or FeCr18Ni15Mo3, which serve as a binder and give the sprayed coatings additional corrosion resistance. The composites produced were assessed based on metallographic examination and wear testing. The results show how the structure of the SHS powder changes due to the injection molding process and how the tribological properties of the HVOF layers are influenced by spraying conditions and the formation of mixed carbides. Paper text in German.

In this paper, metal matrix composite layers are produced by thermal spraying using cored aluminum wire. Two types of wire were produced, one containing mechanically alloyed Al and Cr 2 O 3 powders, the other, Al and AI 2 O 3 . The powders undergo self-propagating high temperature synthesis during the spraying process, which has a positive effect on coating properties such as bonding, cohesion, and wear resistance. Different spraying methods were used in the experiments, but satisfactory results were only achieved via atmospheric plasma spraying. Paper text in German.

This article investigates composite powder materials based on double chromium and titanium carbides with nickel-chromium binder produced using self-propagating high-temperature synthesis. It focuses on the hypersonic velocity oxygen fuel coatings from the synthesized powders. Laboratory tests were focused on the solid particle erosion which occur in energy production systems such as fluidized bed combustors, advanced pulverized cool boilers, and entrained coal gasifiers. Tests were conducted at elevated temperature in a blast nozzle type of tester using bed or fly ashes retrieved from the operating CFB boilers. It was observed that, when adjusting carbide phase composition and chromium content in titanium carbide solid solution, one can control the oxidation kinetic and wear resistance of the material. Fine-grained structure and high cohesion strength of the composite materials formed during synthesis provide their excellent elevated temperature erosion performance in a wide range of test conditions.

It has been shown that high velocity oxy-fuel (HVOF) thermal spray coatings with good wear resistance can be produced from Ni(Cr)-TiC powders manufactured by self-propagating high temperature synthesis (SHS) reactions. In the present work the process was expanded to include additions of Mo and W with the objective of modifying the carbide phase in an attempt to increase the wear resistance further. The effect of changing the matrix, i.e. substituting Fe for Ni, and changing the ceramic phase from TiC to TiB 2 was also examined. The feedstock powder and resultant coatings are characterised in terms of x-ray diffraction analysis and scanning electron microscopy while the coating properties are measured by microhardness and dry sand rubber wheel (DSRW) abrasive wear testing. The results show that Fe(Cr)-TiB 2 and Ni(Cr)-(W, Ti)C coatings have wear rates comparable to that of conventional Cr 3 C 2 -NiCr coatings produced from sintered and crushed powder, but further improvements are needed to achieve the wear resistance of WC-Co coatings.

The properties of thermal sprayed coatings depend mainly on the thermal and kinetic energy of the spray particles. Increase of thermal energy of sprayed particles can be realized using exothermic reactions between components in sprayed particles. Self propagating high temperature synthesis (SHS) is especially suitable to benefit from released energy in the spraying process. At present most commonly used spray material with exothermal reaction is Ni+Al. However, the highest amount of heat is produced in the reactions of aluminium and metal oxides. Of special interest are Cr 2 O 3 , NiO, CuO and V 2 O 5 because they obtain high reaction energies. Furthermore products of the reaction are of special, functional interest like NiAl as bonding agent or alumina as a wear resistant coating. To assure good contact between reacting substances (Al/Oxides) powders for plasma spraying were prepared by mechanical alloying. Calorimetric investigations of plasma sprayed coatings prove that during spraying Al reacts exothermically with oxides. Increase of oxide contents improves coating adhesion/ cohesion properties, hardness, and reduction of porosity. Results are discussed on the base of light microscopy, scanning electron microscopy (SEM) and X-ray structure analysis (XRD).

The following contribution deals with carbide composite powders. These composite powders were made by the SHS-process. The present work is a result of a co-operation between the Institute for Powder Metallurgy Minsk (PMI) and the Department of Composites and Surface Technology at the Chemnitz University of Technology (TUC). The main aspect of this research activity is the improvement of the wear protection due to the deposition of the composite coatings. Paper text in German.

Due to their attractive combination of properties (high resistance to oxidation and wear, high melting point, and lower density) iron and nickel aluminides show promise for the development of advanced materials and coatings However, poor room temperature ductility and susceptibility to intergranular cracking restrict their commercial application. To provide the structure required composite materials produced by the self-propagating high-temperature synthesis (SHS) are promising. In this paper, the potential of thermally sprayed NiAl/aluminum oxide and FeAl/aluminum oxide composite powders produced using the SHS method is evaluated. The results of the structure and property investigations for the synthesized powders as well as for the resulting plasma coatings are presented. Paper includes a German-language abstract.

TiC-based coatings have proven to be very suitable candidates in various areas of thermal spraying when high corrosion and wear resistance is required. The most important advantages of these coatings are their high corrosion resistance compared to conventional coatings such as WC+Co and WC+Co+Cr, but also their low density. However, the main problem with HVOF spraying these materials is their high reactivity with the oxygen necessary for the flame. In this paper, Self-Propagating High-Temperature Synthesis-TiC+Ni-Ti base powder are processed with two different spray guns (Diamond Jet Hybrid (DJH) and CDS 100). This allows to compare the properties of the resultant coatings (wear and corrosion mainly) as a consequence of the main advantages of each variable (gun and gas) particularly in relation to the oxidation processes. It is observed that DJH coatings showed the best corrosion resistance whilst CDS coatings showed a corrosion potential closer to the steel value. Paper includes a German-language abstract.

The poblems of metal-titanium carbide coatings processing by air, low pressure and underwater plasma as well as high velocity oxygen fuel spraying are under consideration. Among the different methods of metal-TiC powders production, like mixing of carbides with scale structure metals, agglomeration with binders, a matter of special interest is the high temperature synthesis of TiC in presence of metallic alloy. The characteristic features of these materials include the carbide phases forming, their bonding with the alloy and reactions during spraying, grain size and their distribution, alloy behavior during synthesis and spraying. Finally, the abrasive wear and erosion resistance of Al-Si/TiC, Fe-Cr/TiC and Ni-Cr/TiC coatings is analyzed.