Cobalt chromium (CoCr), a well-known biocompatible material, was additively manufactured using direct energy deposition (DED) technology in this study. Since DED is a relatively new addition to additive manufacturing (AM) processes, there is not enough information about important properties of fabricated parts and components using this technology. This study investigates some important mechanical characteristics of the additively manufactured CoCr using a variety of numerical simulation methods in addition to mechanical tests and experiments. Mechanical experiments such as hardness, wear, and flexural bending test were conducted on DED processed samples. All experiments were also conducted on conventionally processed CoCr specimens for comparison purposes. This study attempts to explain mechanical properties in terms of microstructural characteristics of each sample. DED processed CoCr samples exhibited a complex microstructure with a variety of features such as cellular, columnar, and equiaxed grains within their melt pools. While the DED processed sample had a lower hardness compared to the conventionally processed one, it exhibited a higher wear resistance. These results were discussed in terms of microstructural characteristics and metallurgical bonding knowing that porosity level was negligible in both samples. The out-of-plane mechanical strength of CoCr samples was measured by conducting flexural bending test, and the conventional sample showed a higher flexural modulus than the DED sample. The bend tests were also numerically simulated using two different finite element analysis (FEA) procedures. The FEA results for the DED and conventionally processed samples follow the same trend as the results obtained from the experimental flexural bending test. The layer structure and interfacial bonding of the DED sample could have contributed to the lower flexural modulus compared to the conventional sample.

The application of cold spray (CS) for additive manufacturing (CSAM) of structural components using metallic materials has recently attracted much attention. However, there are limited reports on developing thick deposits or components with high entropy alloys (HEAs) via CSAM and investigating the microstructural evolution and mechanical properties after deposition and subsequent annealing heat-treatment. This work investigated the microstructure and mechanical properties of asdeposited and heat-treated thick CoCrFeNiMn HEA deposit fabricated via CSAM. The microstructure of the HEA deposit and after heat-treatment were characterised using scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), and x-ray diffraction (XRD). The microstructural analysis reveals heterogeneous grain size distribution with ultrafine grains at the particle-particle interfacial regions and coarse grains at the particle interiors in the as-deposited sample. The as-deposited sample, characterised by moderate porosity, was consolidated following the heat treatment at different temperatures. Additionally, increasing the temperature increases grain sizes resulting from static recovery and recrystallisation, with annealing twin formed at higher temperatures. Most notably, phase decomposition of the deposit microstructure occurs at 600 ºC, with Cr-rich phase particles formed at regions of high dislocations and grain boundaries. Nano-and micro-hardness and tensile testing of micro-flat dogbones samples were performed on the as-deposited and heattreated samples. The effect of heat-treatment on the microstructure and mechanical properties of the cold-sprayed HEA deposit were analysed and discussed.

As steam power plants continue to move towards higher operating temperatures in order to improve efficiency, materials exposed to the working fluid are subjected to accelerated degradations in the forms of surface oxidation and reduced mechanical properties. In this study, the oxidation behavior of two cobalt base alloys, CoCrMoSi (T14) and CoCrNiMoSi (T19), was evaluated in superheated steam (SHS, 0.1MPa) at 800 °C for up to 500 hours. After the exposure, both T14 and T19 alloys experienced weight gain caused by oxidation. Visual observation and SEM surface analysis revealed that T19 had greater extent of surface oxide spallation than that seen on T14. From the cross-sectional evaluation, however, a thin, adherent oxide layer was found to have formed on T19. T14 in fact had suffered from excessive internal oxidation and the surface oxide was uneven. Based on the results obtained so far, it is believed that the finer Laves phase combined with greater amount of Cr in alloy T19 have enabled the formation of a protective oxide layer and thus reduced the extent of internal oxidation. Due to the extensive oxidation ingress along the large Laves phase, it is concluded that T14 is not suitable for applications in SHS at 800 °C.

Ceramic coatings are often applied to metallic substrates using a bond coat to promote adhesion. The corrosion environment between the substrate and ceramic layer can be very harsh due to the absence of dissolved oxygen, high concentrations of corrosive electrolytes, and galvanic and crevice corrosion mechanisms within the bond coat itself. This study assesses the performance of several bond coats in sulfuric acid, including plasma sprayed tantalum and HVOF sprayed NiCr, Hastelloy C, and Ultimet. The bond coats were deposited on Hastelloy substrates and covered with a Cr 2 O 3 topcoat. Electrochemical polarization and open circuit potential measurements were recorded and coating microstructures were examined before and after the corrosion tests. Plasma sprayed tantalum exhibited the best corrosion resistance at room temperature, followed by HVOF sprayed Hastelloy C.

This study evaluates the hot corrosion behavior of NiCoCrAlY, NiCoCrAlYHfSi, NiCoCrAlTaReY, and CoCrAlYTaCSi coatings on 1.4923 stainless steel, applied by high-pressure HVOF spraying. All coatings were cycled in in an environment of Na 2 SO 4 and 82% Fe 2 (SO 4 ) 3 at 690 °C. Each cycle consisted of 1 h of heating in a silicon carbide tube furnace followed by 20 min of cooling. Weight change measurements were performed after each cycle to track corrosion kinetics, and SEM and EDS analysis were employed to analyze the corrosion mechanism. CoCrAlYTaCSi showed the best corrosion resistance of the coatings tested.

This work investigates the high-temperature oxidation kinetics of CoCrAlSiY coatings with different Si concentrations. Hot-corrosion resistance is determined at 800 and 900 °C via hot salt coating, thermal shock resistance is measured at 1050 °C, and the oxidation and corrosion products are analyzed through mineralogical and micro analysis. The results show that Si promotes the formation of an Al 2 O 3 film that improves oxidation and corrosion resistance, but excessive amounts reduce thermal shock resistance.

Due to their superior wear resistance and oxidation behavior, Stellite coatings are widely used in industrial applications where they are exposed to high temperature. Common processes for applying Stellite coatings include high-velocity oxyfuel spraying, laser cladding, and plasma transferred arc welding. Although Stellite welding consumables are available, there are few studies on arc-sprayed Stellite coatings in the literature. This work investigates the microstructural characteristics of an arc-sprayed deposit produced using a CoCr-based cored wire with 4.5 wt% W. The deposit is examined both in its as-sprayed state and after high-temperature exposure. Microstructure formation is assessed via SEM and EDX analysis, phase transformation processes are determined by XRD analysis, and friction and wear properties are measured. The findings are presented and discussed and compared with those obtained from conventional CoCr-based coatings.

Corrosion resistance of coatings deposited by thermal spraying technology HVOF (High Velocity Oxygen Fuel) requires high density in coating and good adhesion to substrate material. The majority of thermally sprayed materials meet the requirements of high corrosion resistance in terms of their composition. However, porous structure raises doubts about the performance of thermally sprayed coatings regarding sufficient protection to the base material. In fact, corrosion protection is a basic coating function. However, , no sufficient attention has been dedicated to the issue of component protection against corrosion attack using HVOF sprayed coatings. In this study, NiCoCrAlY, NiCoCrAlTaReY, NiCoCrAlYHfSi, and CoCrAlYTaCSi coatings were deposited on the substrate material 1.4923. The coatings were deposited using HP/HVOF (High Pressure / High Velocity Oxygen Fuel) thermal spraying technology. The coatings were exposed to the corrosive-aggressive environment in the form of molten salts mixture with composition of 60 % V 2 O 5 and 40 % Na 2 SO 4 at the selected temperature of 750 °C. Further, all coatings were exposed to cyclic conditions. Weight changes of individual specimens were measured after every cycle and results were recorded in diagrams. After the corrosion test, all evaluated coatings were analyzed using scanning electron microscope (SEM), analysis of elemental composition (EDS) and X-Ray diffraction. The NiCoCrAlY and NiCoCrAlTaReY coatings showed the best corrosion protection in selected corrosive aggressive environment, forming the protective oxide layer that prevented further corrosion attack. On the contrary, NiCoCrAlYHfSi and CoCrAlYTaCSi coatings were found not to be suitable for corrosion protection of components working in selected corrosive environment.

Due to good performance in abrasive and sliding wear and enhanced oxidation behavior, coatings based on Co-Cr-W alloys are widely used in industrial applications, where the material is exposed to high temperature. Within the scope of this study, a Co-based alloy similar to commercial Stellite 6, which additionally contains 20.6 wt.% of vanadium, was deposited by Twin Wire Arc Spraying (TWAS). Multi-criteria optimization using statistical design of experiments (DoE) have been carried out in order to produce adequate coatings. The produced coatings have been analyzed with respect to their tribological behavior at elevated temperatures. Dry sliding experiments were performed in the temperature range between 25°C and 750°C. Oxide phases were identified in the investigated temperature range by X-ray diffraction (XRD) using synchrotron radiation. The V-doped Stellite-based coating possesses a reduced coefficient of friction (COF) of about 0.37 at elevated temperatures (above 650°C), which was significant lower when compared to conventional Stellite 6 coating that serves as reference. In contrast, both produced coatings feature a similar COF under room temperature. X-ray diffraction reveals the formation of cobalt vanadate and vanadium oxides above 650°C. The formation of vanadium oxides exhibits the ability of self-lubricating behavior, thus leading to enhanced tribological properties.

The CoCrAlSiY alloy powder with Si mass concentrations of 0, 2% and 5% was prepared in this work. The oxidation kinetics curves of all three kinds of powders after 300 h oxidation at 1000 °C were plotted. In addition, the phase constitution of alloy powder and the distribution of β phase were analyzed by SEM and EDS. Furthermore, the effect of Si-addition on the melting temperature and oxidation resistance of the alloy powder were investigated by DSC-TG from the room temperature to 1400 °C. And the element concentrations at the grain boundary of alloy powder with Si addition of 2% were also analyzed. The results show that the melting temperature of alloy powder decreases as increasing Si content, which indicates that adding Si element could influence on the selective oxidation of Al and Cr elements in the alloy system, and improve the oxidation resistance of CoCrAlY powder. In addition, the weight gain of powder with Si addition of 2% is lowest. And Si element has a enrich tendency in the grain boundary. Therefore, the higher Si content would have a negative effect on the high temperature oxidation resistance of powder.

Cr 3 C 2 -25%NiCr, Stellite 6, NiCrBSi and Hastelloy C-276 coatings were deposited on substrate material P91 by HP/HVOF (High Pressure / High Velocity Oxygen Fuel) thermal spraying technology. The resistance against high temperature corrosion was evaluated exposition of coatings to corrosive-aggressive environment in the form of molten salts mixture with composition of 60% V 2 O 5 and 40% Na 2 SO 4 at temperature of 750 °C. Further, coatings were exposed to cyclic conditions. After the corrosion tests, all coatings were analyzed using scanning electron microscope (SEM), and analysis of elemental composition (EDX). Alloys-based coatings showed very similar corrosion mechanism in the selected aggressive environment and the same can be stated about cermet coatings. The obtained results prove that HVOF deposited coatings can replace current surface protection of components in power equipment such as nitriding.

This work introduces a hybrid spray-and-fuse process and a modified CoCrMoC (Stellite) alloy that significantly expand the manufacturing window for wear-resistant coatings. The Co-based alloy was produced by adding Ni, B, and Si to Stellite 720 to lower its melting points and expand its melting range thereby improving the sprayability and fusibility of the material. The modified alloy was deposited on Inconel 718 balls and 1 in. diameter coupons by HVOF spraying and coating samples were sinter fused at high temperatures followed by furnace cooling. The processes used are described and test results are presented, showing that thick, metallurgically bonded coatings were achieved with high hardness and excellent wear and corrosion resistance.

A nanostructured WC-CoCr coating was fabricated by HVOF spraying using a new type of WC-CoCr powder in which the CoCr exists in the form of a metallic compound. The CoCr powder constituent was prepared by induction melting and mechanical milling. It was then combined with a WC-Co composite nanopowder and the mixture was agglomerated by spray drying and heat treating. The powders and coatings produced were characterized by means of XRD, EDS, and BSE analysis, nanoindentation testing, and potentiodynamic polarization studies. The results show that the presence of the intermetallic CoCr compound makes nanostructured WC-CoCr coatings harder and much more corrosion resistant than conventional WC-Co-Cr coatings in which Cr exists as an unalloyed metal.

This paper evaluates and compares five wear-resistant coatings produced by HVOF spraying for high-temperature use. CrC-NiCr, CrC-CoNiCrAlY, Stellite 6, NiCrBSi, and TiMoCN-Ni coatings were sprayed on grit-blasted carbon steel substrates. Abrasive, sliding, and fretting wear resistance were measured and changes in microstructure and hardness due to high-temperature exposure were recorded. CrC-NiCr coatings exhibited the best wear properties, but the oxidation of carbides at high temperatures proved to be a problem. Based on test results, alternative coatings would include CrC-CoNiCrAlY for abrasive wear, Stellite 6 for erosive wear, and NiCrBSi for sliding wear.

In this study, MoB-CoCr composite coatings are deposited on low-carbon steel substrates by HVOF spraying and salt spray tests are conducted to qualitatively evaluate coating density. Test samples with optimized dense coatings showed no rust after 300 hours in a salt spray. Samples with porous coatings, on the other hand, showed signs of rust after just 24-48 hours. Test samples protected by the dense composite coatings, as confirmed by salt spray testing, were undamaged after 90 days of immersion in a Zn-0.2%Al galvanizing bath at 460 °C.

This study investigates the density, hardness, and wear behavior of WC-Co-Cr coatings produced by high-velocity air fuel (HVAF) spraying. The results indicate that coating hardness, density, and wear performance are improved by increasing gas velocity and using powders composed of fine CoCr particles.

In this study, WC-CoCr coatings are deposited on grit-blasted steel substrates by high-velocity airfuel (HVAF) spraying. A cross-sectional image of the feedstock powder shows that the WC grains are evenly distributed in the Co-Cr matrix. As-sprayed coating cross-sections are examined under different levels of magnification, coating hardness is measured, and coating and powder phases are analyzed by XRD. In addition, the corrosion behavior of coated and uncoated substrates is analyzed and compared with a reference hard chrome coating.

The excellent corrosion resistance and biocompatibility of titanium make of it the material to choose for biomedical applications. Cold spraying, as a new coating technique, can be used to deposit protective Ti coatings onto less performing materials such as stainless steel and Co-Cr alloys, commonly used for biomedical implants. In addition, Cold Spray has the advantage, in comparison with conventional thermal spray techniques, to permit the deposition of oxygen-sensitive materials. In this study, Cold Sprayed Ti coatings were prepared on Co-Cr alloy substrates by using different spray process conditions. The microstructure of coatings was observed by SEM and the inner porosity was estimated by image analysis. Oxygen and nitrogen contents were investigated on a set of free standing deposits obtained using different process parameters. In the same way, the roughness and microhardness of deposits, such as the adhesion strength with the substrate, were measured. Finally, the corrosion performance of the coatings was evaluated by mean of open circuit potential measurement (OCP) and potentiodynamic polarizations scans. The electrochemical response was therefore discussed and compared to the corrosion behaviour of the Co-Cr alloy substrate and the bulk Titanium.

MoB/CoCr, a novel material for thermal spraying, with high durability is used to resist erosion by molten Al-12.07wt%Si alloy. The durability of the MoB/CoCr coating prepared by low pressure plasma spraying (LPPS) has been investigated using a molten-metal immersion tester. The test revealed that the MoB/CoCr coating has much higher durability without dissolution in the molten Al-12.07wt%Si alloy. Little change of crystal structure, mainly composed of ternary borides of Co 2 MoB 2 and CoMoB, is observed after the immersion test, suggesting that the ternary borides have much higher durability.

This study assesses the potential of kinetic-spray coatings for dealing with the effects of soldering and erosion on aluminum casting dies. In the experiments, molybdenum-boride cermet and cobalt-based alloy powders are cold sprayed onto SKD61 substrates. Coating microstructure is assessed via SEM and XRD analysis and several mechanical properties are measured. In order to evaluate soldering resistance, the coatings are immersed in a molten aluminum bath. Although cold-sprayed CoCrNiWC exhibited high coating density and low porosity, its soldering resistance was significantly lower than that of MoB-NiCr. The boride cermet coating not only exhibited superior soldering resistance, but also higher hardness, bond strength, and wear resistance. However, its deposition efficiency needs further improvement.