Manufacturing of steel components is often done at high temperatures (HT) posing a serious challenge to components such as forming tools. Thermal spray coatings provide a cost-effective solution for surface protection under HT, corrosive environments and severe wear conditions. Thermally sprayed coatings based on cubic hard materials such as TiC and TiCN can provide an alternative to widely used Cr3C2-NiCr. While the latter possess a superb oxidation resistance and wear resistance at HT, they are prone to degradation in the presence of Mn, an element commonly alloyed in many modern steel grades such as TWIP (twinning-induced plasticity steel). In this study, a (Ti,Mo)(C,N)-29% Ni hardmetal feedstock powder was prepared by agglomeration and sintering. Coatings were deposited using a high velocity air-fuel (HVAF) spray process. The coating was benchmarked against a standard Cr3C2-NiCr coating obtained with the same spray process. Our work comprises analyses of the feedstock powder along with the resulting coating microstructure after deposition and heat treatment. Further, the HT sliding behavior against TWIP steel using a HT pin-on-disc tribometer at 700°C was investigated. The results showed a clear benefit of the TiCN-based coating, with almost no wear detected, while the Cr3C2-coating showed a significant wear loss. Based on these results, the TiCN-based coating is regarded as potential solution for prospective forming applications of modern high Mn steels, such as TWIP.

In general, similar MAX-Phase coatings are considered as oxidation protection layer for preventing disastrous reactions of the Zircaloy fuel rods during a cooling water failure in a nuclear power plant. For the present study on Aerosol Deposition, Ti3SiC2 was selected as MAX-phase model system due to the availability of property data and commercial powder. The as-received powder was milled to different nominal sizes. For revealing details on coating formation and possible bonding mechanisms, Aerosol Deposition experiments were performed for different particle size batches and process gas pressures. Microstructural analyses reveal that coating formation preferably occurs for particle sizes smaller than two microns. Using such small particle sizes, crack-free, dense layers can be obtained. The individual deposition efficiencies for the different particle sizes, particularly the critical size below which deposition gets prominent, vary with process gas flows and associated pressures. Detailed microstructural analyses of coatings by high resolution scanning electron microscopy reveal plastic deformation and fracture, both attributing to shape adaption to previous spray layers and probably bonding. In correlation to coating thickness or deposition efficiencies, respective results give indications for possible bonding mechanisms and a tentative window of Aerosol Deposition for Ti3SiC2 MAX-phases as spray material.

This study evaluates the possibility of depositing hard B 4 C and TiC reinforcing particles in a Ni matrix using low-pressure cold spraying. It also investigates the effect of particle velocity and kinetic energy on deposition efficiency, microstructure, hardness, and wear resistance. B 4 C and TiC powders were blended at 50, 75, and 92 wt% carbide content with Ni powder comprising the remainder of the mixture. The impact velocity of sprayed carbide particles was calculated using a mathematical model based on the thermodynamics of compressible fluid flow through a converging-diverging nozzle. The model showed that the kinetic energy of TiC particles prior to impact was three times smaller than that of B 4 C, resulting in a higher carbide content (18 wt% compared to 8 wt%) due to reduced fracture and rebound of the TiC particles. Although the hardness values of both coatings are within the range of cold-sprayed WC-Co-Ni, wear rates were found to be high.

In the present work, commercially available NiCr and NiCr-TiC powder blends were deposited on boiler steel substrates by HVOF spraying. To evaluate coating performance, bare and coated steel samples were placed in the superheater zone of a coal fired boiler for 15 cycles. Weight change and thickness loss were measured and the results were used to establish erosion-corrosion kinetics. XRD and SEM/EDS techniques were used to analyze the microstructure and phase composition of as-sprayed and eroded-corroded specimens. The improvement in erosion-corrosion resistance provided by the coating may be attributed to the formation of nickel and chromium oxides and spinels.

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.

In this study, titanium carbonitride (TiCN) coatings are obtained by atmospheric plasma spray synthesis, or reactive plasma spraying. In order to promote reactions between Ti particles and reactive gases, an extended gas tunnel was mounted at the end of a conventional plasma gun. The oxidation behavior of the TiCN coatings was investigated over a wide temperature range, showing that the coatings suffered severe oxidation at temperatures above 700 °C and were entirely oxidized to the TiO 2 phase at 1100 °C. The principal oxidation mechanism was revealed, indicating that oxygen can penetrate into the TiCN coatings at high temperatures. Changes in microhardness were also investigated as a function of temperature, showing a precipitous drop over the range of 700-1100 °C.

Thermally sprayed Fe-based coatings reinforced by TiC particles are a cost effective alternative to carbide coatings such as WC/CoCr, Cr 3 C 2 /NiCr and hard chrome coatings. They feature a good wear resistance and, with sufficient amount of alloying elements like Cr and Ni, also a high corrosion resistance. In hydraulic systems the piston is coated for protection against corrosion and wear. New water-based hydraulic fluids require an adaption of the coating system. In order to investigate the wear and corrosion resistance of Fe/TiC a novel powder consisting of a FeCr27Ni18Mo3 matrix and 34 wt.-% TiC was applied by HVOF and compared to reference samples made of WC/CoCr (HVAF) and hard chrome. Besides an in-depth coating characterization (metallographic analyses, EMPA), wear resistance was tested under reverse sliding in a water-based hydraulic fluid. Corrosion resistance was determined by polarization in application-oriented electrolytes (hydraulic fluid at 60 °C, artificial sea water at RT).

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 paper presents the results of a study on the tribological properties of TiC-based coatings deposited by HVOF spraying. Four powder feedstocks consisting of (Ti,Mo)(C,N) hardmetal with Ni and Co binders were prepared by agglomeration and sintering. The feedstocks differ in composition and particle size distribution, the latter being optimized for fuel type and equipment requirements. Coating specimens are evaluated based on microstructure, hardness, bonding strength, and friction and wear behavior. The results are presented and correlated with spray parameters, equipment differences, and feedstock characteristics.

Compounds of the material group known as MAX phases combine metallic and ceramic properties. In this work, MAX-phase coatings are deposited from modified Ti 3 SiC 2 and Ti 2 AlC commercial feedstock powders using HVOF and atmospheric plasma spraying (APS). Feedstock powders and coatings were studied by microscopy and XRD. Despite the use of unoptimized powders, well adhering and relatively dense coatings were produced. HVOF-sprayed layers had denser microstructures with higher amounts of MAX phases. Optimizing the shape and particle-size distribution of feedstock materials is expected to improve coating properties.

Considerable effort has been made to translate the beneficial properties of bulk Ti(C,N)-based hardmetals to wear resistant thermal spray coatings. Such efforts have focused primarily on as-sprayed coatings. However, past work has shown that hardmetal coatings can undergo significant changes when operated at elevated temperature for extended periods. This work characterised the microstructural changes in a HVOF sprayed (Ti,Mo)(C,N)-Ni coating treated in air at 700°C for up to 30 days. The microstructural development of the carbonitride phase was very subtle. Image analysis indicated that the Mo-rich rim phase underwent the greatest degree of dissolution during spraying and precipitation with heat treatment. Dissolution of the carbonitride phases during spraying led to significant alloying of the Ni binder. Rapid recovery of the Ni binder composition occurred after one day of treatment, but it retained a higher steady state degree of alloying relative to the starting powder.

HVOF-sprayed carbide based coatings such as WC/Co or Cr 3 C 2 /NiCr are industrially well established for wear and corrosion protection applications. Due to their high carbide content of typically 75 wt.-% and more, they are providing a very high hardness and excellent wear resistance. Unfortunately costs for matrix materials like Ni or Co underlie strong fluctuations and are significant higher compared to iron. Therefore an alternative concept to the conventional carbides is based on TiC-strengthened low cost Fe-base materials, which are already in use for sintering processes. Depending on the carbon content the Fe-base material can additionally offer a temperable matrix for enhanced wear behaviour. Within this study the sprayability of TiC-strengthened Fe-powders with a gaseous and a liquid fuel driven HVOF-system has been investigated. The resulting coatings have been analysed with respect to microstructure, hardness and phase composition and compared to galvanic hard chrome, HVOF-sprayed and remelted NiCrBSi and HVOF-sprayed Cr 3 C 2 /NiCr (80/20) coatings as well as sintered Fe/TiC reference materials. Furthermore the Fe/TiC coatings have been heat treated to proof the retained temperability of the Fe-matrix after thermal spray processing. For determination of wear properties tribometer tests have been conducted. Currently the corrosion resistance of the sprayed Fe/TiC coatings is investigated as well the wear behaviour in a practical hydraulic test bench.

Three types of cobalt-based cermet coatings were prepared by high velocity oxy-fuel (HVOF) spraying using cobalt- clad TiC-50Co, SiC-50 Co and WC-18Co powders. The microstructure of three coatings was characterized using a scanning electron microscope (SEM). The adhesive strength of the coatings was tested according ASTM C633-79 standard. The hardness of three coatings was measured using a HV-5 Vickers hardness tester. The abrasive wear performance of the coatings was examined by a dry-sand rubber wheel tester according to ASTM G65-61 standard. The results show that the density, thermo physical properties and volume fractions of the solid carbide phases in the spray particle have a significant influence on the adhesive strength of the coatings. The hardness of WC-18Co coating is higher than that of TiC-50Co and SiC-50 coatings and is much lower than WC-17Co coating deposited with sintered-crushed powders. Moreover, the abrasive wear volume loss of the WC-18Co coating is about 60 times higher than that of the WC-12Co coating sprayed by sintered-crushed powder, and greatly lower than that of TiC-50Co and SiC-50 coatings. The wear mechanisms of three coatings are discussed.

Iron base composite coatings were deposited on mild steel substrates by arc spraying and cored wire with TiC ceramic powders. The abrasive wear resistance properties were examined on the MLS-225 wet sand/rubber wheel tester. The microstructure, phase compositions and worn surface morphologies of the coatings were observed by means of optical, scanning electron microscopy and X-ray diffraction. The results showed that composite coatings with TiC ceramic hard phases were reinforced by the TiC hard particles distributed in the iron-based coating. The average micro hardness of the coatings is about 1137 HV0.1. The coatings have the excellent abrasive wear resistance which is 6 times higher than that of the Q235 mild steel. Wear mechanisms of coatings was mainly micro-ploughing and brittle fracture.

The specific advantages of TiC as a hard material are its low density, high hardness and the high alloyability of the hard phase - binder metal composite. Currently developed agglomerated and sintered core-rim structured TiC-based powders were intensively studied in the last few years for thermal spray coating solutions. In the work described in this paper two different powders with cubic (Ti,Mo)C and (Ti,Mo)(C,N) hard phases and Ni/Co binder, representing the first and second alloying step for the binary TiC-Ni/Co composite, were used together with mechanically mixed NiBSi powder to produce wear resistant coatings by plasma-transferred arc welding (PTA) and laser cladding. Basic process parameters, coating microstructures and properties are described. Coatings with fine grained hard particles were obtained by both processes, while the coating prepared from the nitrogen-containing powder by laser cladding shows a significant smaller hard particle grain size and increased hardness.

The present study was carried out within the scope of a project oriented toward the evaluation of applicability of different materials as thermally sprayed coatings for gear flank protection. Investigations were made on APS deposited oxide coatings, such as Cr 2 O 3 and Magnéli phases of different systems, as well as on hardmetal coatings based on WC, Cr 3 C 2 and TiC deposited by HVOF. All coating microstructures were investigated by optical microscopy, with selected samples studied additionally by SEM. Phase composition, hardness, Young’s modulus and fracture toughness were other basic coating properties studied. An oscillating sliding wear test was used as the main tool for preliminary evaluation before more laborious testing. The wear resistance in this test was investigated against 100Cr6 for all materials as well as against sintered silicon nitride and sintered WC-Co for oxide and hardmetal coatings, respectively. Hardmetal coatings based on WC and TiC showed the best results and were selected for further testing.

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.

Advanced TiC-based spray powders contain molybdenum and nitrogen as alloying elements and consist of core-rim-structured (Ti,Mo)(C,N) hard phases embedded in Ni, Co or mixed Ni/Co binder phases. For the investigations of the present study, four powders with binder phase contents of 29 and 39 mass-%, corresponding to about 20 and 27 vol.-%, respectively, were prepared by agglomeration and sintering. Coating samples were sprayed using JP-5000 equipment and two spray parameter sets. During coating characterization, special emphasis was placed on the changes in chemical (carbon loss and oxygen uptake) and phase compositions during spraying and their correlation to the coating microstructures and properties. It was found that the decreases in carbon and nitrogen contents were practically independent of the spray parameters for all of the four powders, whereas the oxygen uptake was different for each of the powders. The effect of the oxygen content on different coating properties is discussed in detail. All coatings investigated in this work showed excellent properties. It is anticipated that TiC-based coatings sprayed from these types of advanced powders can complement thermal spray coating solutions based on WC and Cr 3 C 2 .

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.