Thermal Spray Processes for the Repair of Gas Turbine Components

Fiebig, Jochen; Bakan, Emine; Kalfhaus, Tobias; Mauer, Georg; Guillon, Olivier; Vaßen, Robert

doi:10.1002/adem.201901237

Cited by 18 publications

(10 citation statements)

References 75 publications

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“…Its main features will be mentioned in the later section. Since atom diffusion occurs across the intersplat and coating/substrate boundaries at high temperature, the post-spray heat treatment usually leads to healing of unbonded interface boundaries and reducing of small pores in the coating (Ref 32 , 33 ). For metallic coatings especially MCrAlY bond coats for thermal barrier coatings, high temperature heat treatment in vacuum or inert gas atmosphere not only leads to full densification of the bond coat itself but also the formation of metallurgical bonding between the superalloy substrate and the bond coat (Ref 34 , 35 ).…”

Section: Introductionmentioning

confidence: 99%

“…For metallic coatings especially MCrAlY bond coats for thermal barrier coatings, high temperature heat treatment in vacuum or inert gas atmosphere not only leads to full densification of the bond coat itself but also the formation of metallurgical bonding between the superalloy substrate and the bond coat (Ref 34 , 35 ). The HIP (hot isostatic pressing) treatment is more effective to densify metallic coatings (Ref 32 , 33 ). The heat treatment needs to be carried out at a high temperature either in a vacuum chamber or in a controlled inert atmosphere.…”

Section: Introductionmentioning

confidence: 99%

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Recent Research Advances in Plasma Spraying of Bulk-Like Dense Metal Coatings with Metallurgically Bonded Lamellae

Luo

Dong

et al. 2022

J Therm Spray Tech

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Although thermal spray metallic coatings have been widely used for materials protection from wear, corrosion and oxidation, its porous feature limits the full utilization of materials potential. Moreover, the oxidation inherent to thermal spraying in the ambient atmosphere is detrimental to interlamellar bonding formation, which further degrades the performance of thermal spray metal coatings. How to tape out the full potential of spray materials in the form of the coating is a still great challenge to thermal spray coating technology. Facing such challenge, recent efforts have been made to deposit dense metallic coatings with sufficiently bonded lamellae by oxide-free molten droplets through atmospheric plasma spraying. In this paper, the strategies for depositing bulk-like metal coatings will be reviewed. The formation of the bulk-like coating through post-spray treatments is briefly reviewed including post-spray heat treatment and laser remelting following the brief introduction to the features of thermal spray metallic coatings. The effect of the substrate preheating temperature on the splat formation and subsequently the adhesion formation was examined to reveal the dominant limitation of resultant oxide scale. Then, the role of the deposition temperature on the formation of bulk-like metal deposits with neglecting the effect of oxidation during spraying by vacuum plasma spraying practices is shortly presented. The recent progress on the new strategies to develop spread-fusing bonding mechanism and in-situ in-flight deoxidizing mechanism through developing ultra-hot metallic droplets will be introduced. The thermodynamics and kinetics requirements for the in-situ in-flight deoxidizing through deoxidizer elements adding to alloy spray powders for achieving oxide-free molten droplets in the ambient atmosphere are examined. The conditions to develop the spread-fusing mechanism during the spreading of impacting molten metal droplet for metallurgical bonding are presented. It is obvious from this review paper that the realization of two mechanisms depends on both the spray materials design and heating control of in-flight particles. Through the generation of ultra-hot droplets by plasma spraying to achieve oxide-free molten droplets, strategically it will be possible to deposit bulk-like dense metallic coating through spread-fusing of splat surfaces with limited post-spray oxidation. Such strategies will tape out the full potential of coating materials and open up the new application fields for plasma spraying.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Recent Research Advances in Plasma Spraying of Bulk-Like Dense Metal Coatings with Metallurgically Bonded Lamellae

Luo

Dong

et al. 2022

J Therm Spray Tech

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“…In this context, many researchers have been carried out on mold repair technology. Common remanufacturing methods include EDM [2], arc overlay welding [3], thermal spraying [4] and laser cladding technology [5][6], which is widely used because of the advantages of dense organization of the clad layer, high bond strength, low dilution rate and small heat-affected zone.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation and analysis of surface texture on the performance of die steel laser cladding layer

Zhao¹,

Ma²,

Zhang³

et al. 2022

Preprint

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In order to reduce the stresses and cracks generated during the progress of laser cladding and improve the fatigue resistance and service life of the die steel, a simulation study of residual stresses and surface texture is attempted by changing the parameters of the cladding process. Different melting process parameters (power, scanning speed, spot radius) are selected as laser melting simulation factors and the residual stress is used as the main experimental index in this paper. Three-factor, three-level orthogonal simulation experiments are conducted to determine the optimal melting parameters by performing signal-to-noise ratio and extreme difference analysis on the experimental results. The cladding temperature and residual stress distribution are compared between prefabricated texture and non-texture cladding simulation under the optimal cladding parameters. The results of the optimal melting parameters are as follows: laser power of 800 W, scanning speed of 20 mm/s, spot radius of 1 mm, and the minimum residual stress of 360 MPa. In the melting simulation, the average residual stress of the prefabricated clad layer is 149 MPa, which is about 58.56% lower than that of the nonwoven simulation. In addition, the experimental results are in accordance with the simulated results and validate that the residual stresses may be reduced by the prefabricated texture under the premise of ensuring the melting temperature, which in turn can achieve the purpose of reducing the crack generation.

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“…During this process, a focused laser beam, together with powder, that is fed into a high-vacuum chamber by an inert gas, forms a pool on the surface of the substrate material, resulting in the stable connection of materials. The LENS system enables both, repair of parts and surface modification by the application of a protective coating since the process is characterized by high accuracy and purity during laser cladding [ 16 , 17 , 18 ]. An important advantage of using this system from the metallurgical point of view is the narrower heat-affected zone than that usually obtained in the conventional methods.…”

Section: Introductionmentioning

confidence: 99%

“…The resulting laser clads are narrower than those in any other process, and as a consequence, the final part does not require either rough or finish machining. The additive nature of the LENS process makes it a more resource-efficient manufacturing technology since less waste is generated in comparison to the subtractive techniques [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. Additionally, a less amount of the material could be used for the part repair, which is extremely important in terms of the application of nickel-based alloys.…”

Section: Introductionmentioning

confidence: 99%

Suitability of Laser Engineered Net Shaping Technology for Inconel 625 Based Parts Repair Process

et al. 2021

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In this paper, the Inconel 625 laser clads characterized by microstructural homogeneity due to the application of the Laser Engineered Net Shaping (LENS, Optomec, Albuquerque, NM, USA) technology were studied in detail. The optimized LENS process parameters (laser power of 550 W, powder flow rate of 19.9 g/min, and heating of the substrate to 300 °C) enabled to deposit defect-free laser cladding. Additionally, the laser clad was applied in at least three layers on the repairing place. The deposited laser clads were characterized by slightly higher mechanical properties in comparison to the Inconel 625 substrate material. Microscopic observations and X-ray Tomography (XRT, Nikon Corporation, Tokyo, Japan) confirmed, that the substrate and cladding interface zone exhibited a defect-free structure. Mechanical properties and flexural strength of the laser cladding were examined using microhardness and three-point bending tests. It was concluded, that the LENS technology could be successfully applied for the repair since a similar strain distribution was found after Digital Image Correlation measurements during three-point bending tests.

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Thermal Spray Processes for the Repair of Gas Turbine Components

Cited by 18 publications

References 75 publications

Recent Research Advances in Plasma Spraying of Bulk-Like Dense Metal Coatings with Metallurgically Bonded Lamellae

Recent Research Advances in Plasma Spraying of Bulk-Like Dense Metal Coatings with Metallurgically Bonded Lamellae

Numerical simulation and analysis of surface texture on the performance of die steel laser cladding layer

Suitability of Laser Engineered Net Shaping Technology for Inconel 625 Based Parts Repair Process

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