Search Results for coating quality evaluation

This paper presents the AccurasprayHub, a centralized data platform designed to harmonize booth parameters, in-situ plume measurements, maintenance schedules, and coating quality evaluations. By combining domain expertise with advanced analytics, including initial steps toward machine learning, the AccurasprayHub establishes robust datasets, identifies stable process windows, and provides proactive insights for process improvements.

The aim of this study is to compare the quality of corrosion-resistant thermal spray coatings depending on where and how they are applied. ZnAl 15 coatings were applied to S235 steel substrates by wire arc spraying in keeping with standard (EN ISO 2063) practice. The coatings were sprayed under factory conditions and in a simulated onsite environment using manual and automated methods. As-sprayed and sprayed-and-sealed coating samples were subjected to climate-cycle and corrosion testing. Coatings applied onsite varied in quality to a much greater extent than those sprayed under workshop conditions. Poor quality, and implicitly a lower corrosion resistance, was widely detected in coatings where ZnAl was manually sprayed under simulated onsite conditions. The implications of the study are particularly relevant to the sustainability of coastal and offshore wind power generators due to maintenance challenges.

The goal of this work is to have standardized quality control of thermal spray coatings incorporated into the Standard Practices Manuals of all aircraft engine original equipment manufacturer’s around the world. With the many manufacturers’ criteria for evaluation of thermal spray materials, laboratories are forced to have multiple criteria/systems to test and analyze coatings. As airlines/repair shops are moving towards overhaul of more variable engine types/models in their shops, the need to have a common evaluation system has been identified and is currently being addressed. A sub-committee of the European Airline Committee for Materials Technology is currently working to formulate this common system for thermal spray coatings evaluation. Participants are from GEAE, Pratt & Whitney, Rolls Royce, SNECMA and KLM Royal Dutch Airlines. The progress and goals of this group will be documented and reported.

A commercial air carrier has replaced the chrome plating on line-of-sight landing gear installed on several aircraft with HVOF sprayed WC-Co-Cr coatings. Pending the results of ongoing testing and service evaluations, the carrier plans to switch to HVOF coatings on all line-of-site landing gear and possibly other structural and engine components. This paper discusses the infrastructure that will be necessary to build, qualify, and maintain a high-velocity oxyfuel spraying facility that will serve one of the largest fleets of aircraft in the world. Paper includes a German-language abstract.

The high velocity oxyfuel flame spraying (HVOF) process appears to be an interesting alternative to low pressure plasma spraying (LPPS) processes for the application of MCrAlY coatings for the use of hot corrosion protection on turbine parts like blades and vanes. Lower investment costs for HVOF facilities compared to LPPS systems combined with adequate coating properties and a stable, easy controllable process can be seen as potential advantages regarding the application of this process. Several recent HVOF systems are screened concerning the application of MCrAlY coatings for hot corrosion protective coatings on turbine blades. In this research project, the Design of Experiments (DoE) is used to built up factorial experimental designs. The aim is, besides a benchmarking, to find out the potential of the HVOF systems to produce high quality hot corrosion protective coatings. The main emphasis of these preliminary investigations is on the evaluation of bonding defects in the interface, the porosity, and the oxide content of the coatings.

During Thermal Spraying material is partially or totally melted in between milliseconds, accelerated to high velocities and propelled onto the surface to be coated. Different temperatures, velocities and cooling times of the particles arise from different spraying techniques and conditions. The microstructure can be widely varied by tuning the spraying parameters. To optimize the coating properties with respect to a specific function one has to know i) the influence of the spraying conditions on the microstructure and ii) the correlation between microstructure and coating properties. Therefore analyzing methods are needed to determine the microstructure and to characterize mechanical, physical and chemical properties of the coatings. The proposed paper summarizes methods to characterize the microstructure including metallographic techniques, electron microscopy and X-ray analysis. Methods to determine the properties of the coatings including various adhesion tests, residual stress measurement, tribological and corrosion tests will be described in more detail. The increasing importance of Quality Management in all industrial sectors call heavily for reliable, destructive and especially non-destructive characterization techniques of coatings. An overview of common characterization techniques as well as new trends will be given. Recent development of International standardized tests will also be reported.

A comprehensive approach is presented for facilitating the implementation of advanced plasma spray processing technology in the manufacture, repair, and refurbishment of industrial components. This approach employs an integrated methodology for combining several advanced computer-based methods, including: 1) an interactive multimedia-based education and training tool to effectively store and retrieve plasma spray processing information in a variety of formats; 2) an expert system to select plasma spray feedstock material for a specific coating function; 3) a one-dimensional plasma spray process model that allows simulation of plasma spray processing conditions for identifying operational envelopes for a selected feedstock material; 4) an interface fracture model for identifying appropriate acceptance criteria for reduced cracking along the coating/substrate interface; and 5) a set of computer-based nondestructive test methods for performing quality assurance and control. This comprehensive approach and the integrated methodology provide an advanced engineering tool for the selection, optimization and implementation of specific advances in plasma spray processing technologies. A major outcome is the reduced need for expensive and time-consuming trial-and-error methods in evaluating the application of plasma spray coatings for the manufacture, repair, and refurbishment of specific industrial components. This comprehensive approach and integrated methodology can be extended to include other thermal spray processing technologies as well.

This study investigates a new evaluation method that has the potential to differentiate between particle interfaces and grain boundaries in cold spray coatings. The method uses confidence index (CI) and image quality (IQ) values obtained from EBSD analysis to determine the location of grain boundaries as well as grain orientation and crystallinity of the deposit. In the case of a cold-sprayed copper deposit, the new method helps to explain the observed characteristics of the coating.

Nickel based alloys used in coating applications have been the focus of many studies, particularly in the aerospace industry. Their inherent corrosion and oxidation resistant properties have made them especially attractive for use as the metallic bond coat found in thermal barrier coating systems. Cold Spray is an emerging coating technology in which fine powder particles are accelerated in a supersonic flow and then deposited onto a substrate by means of plastic deformation. In this study, conventional CoNiCrAlY coatings and nanocrystalline nickel coatings are produced using the Cold Spray deposition technique. The coating quality is evaluated using scanning electron microscopy as well as porosity and microhardness measurements.

The metallographic process for evaluating thermally sprayed coatings is sometimes viewed as a variable process in the scope of coating evaluation. There is always a question as to whether the failure of a coating is polishing related or an actual change in the spray production process. The use of metallographic standards similar to hardness calibration can be implemented to provide assurance of a repeatable metallographic polishing. Development and use of the standards will be discussed and examples given of the standards principle.

An overview on potential non-destructive testing (NDT) methods for the inspection of thermally sprayed coatings in production lines is given. The suitability of several NDT techniques has been investigated with view on their sensitivity for the detection of defect sizes possibly being critical for Thermal Spray coatings. Eventually, a method is presented that shows qualification for detection of subsurface flaws in coatings such as delaminations and cracks and offers flaw distinction by image analysis procedures. A storage and archiving of test results is possible thus completing full quality control and meeting possible warranty claims. The major advantage of the NDT process is its very high detection speed which guarantees high productivity even for high volume production systems. Thus a full-area detection of large coated components becomes possible. The process is not restricted to plain components, but is usable for the detection of internally coated cylinders as well.

This paper presents an overview of the engineering and innovation behind BMW’s use of thermal spraying in the production of automotive engines at its light metal foundry in Landshut, Germany. It discusses the factors that drive engine development at BMW, the different approaches in play for improving the performance of cast aluminum crankcases, and the opportunities made possible by thermal spray technology. It describes the aluminum crankcase production process, from die casting to honing, with emphasis on BMW’s state-of-the-art implementation of twin wire arc spraying. It explains how the spraying process is controlled and how key process steps and parameters are monitored and optimized in real time along with coating properties and microstructures. If a coating defect is detected, it is documented on the fly and, in many cases, corrected in a subsequent process step. A few examples of defect detection at work are presented.

Nondestructive Evaluation and Testing (NDE&T) techniques have been played vital roles in property characterization, process development and quality control of various thermal spray coatings. Besides conventional NDE&T lab methods such as eddy current test (ECT) for thickness measurement and fluorescent penetrant inspection (FPI) for cracking detection, some latest NDE techniques have been developed, demonstrated and applied to evaluate and characterize thermal sprayed coatings recently. The improved and innovative NDE methods provide more capable and accurate measurement to inspect on surface morphology, 2D and 3D coating porosity, oxide content, interface debonding, as well as other types of coating features, defects or specific properties. In this work, some non-contact NDE techniques and their applications were investigated and discussed based on several case studies of thermal sprayed coatings. Laser confocal microscopy had been used for characterizing surface morphologies and roughness profiles of HVOF WC-based coatings with 2D and 3D mapping methods. In particular, thermal wave imaging and ultrasonic micro imaging methods were used to detect the suspicious existence of lateral coating separation within or at the MCrAlY coating-substrate interfaces. Laser dimension sensoring method exhibited the extended capability of in-situ coating thickening measurements on turbine blade and vane. The latest non-contact NDE techniques demonstrated their unique and strong capability for in-situ and ex-situ coating characterization, process and quality control and coating failure analysis.

The thermal barrier coating (TBC) system is currently a standard technology of gas turbine hot gas path parts to achieve a highly reliable long life operation of engines for a power supply. Mitsubishi Heavy Industries, LTD. (MHI) has applied the TBC on the gas turbine blades, vanes and combustor parts. TBC system consists of MCrAlY as a bondcoat for oxidation protection at elevated temperature and YSZ (yttria stabilized zirconia) as a topcoat for efficient thermal barrier. The conditions where TBC has been in service are at the temperature up to 1500°C and with combustion gas environment. As far as the blades and the vanes are concerned, the MCrAlY bondcoat is coated by low pressure plasma spray (LPPS) or high velocity oxygen fuel (HVOF) system, and the YSZ topcoat is coated by atmospheric plasma spray (APS) system. In the case of the combustor parts, both the MCrAlY bondcoat and the YSZ topcoat are coated by APS. To increase the reliability and prolong the service life of the applied TBC in the gas turbine, it is very important to verify the coating properties, optimize the coating process parameters and control the coating process.

Graded metal-to-ceramic coatings as thermal barrier coating (TBC) have been studied to improve the surface properties of the coating on high-temperature components. The atmospheric and low pressure plasma spray experiments are carried out with partially stabilized zirconia (YSZ and MSZ) and MCrAlY for mixing of functionally gradient materials. Especially, three-layer and five-layer graded TBCs are designed and produced to match gradually the material properties of a substrate and a top coating for reducing thermal stresses. A fully-saturated fractional factorial test is employed to determine optimum process conditions related to the thermal plasma generation, powder feeding, and substrate handling. Microstructural analysis using optical microscope and SEM, compositional analysis by XRD, bond strength test and thermal shock tests are carried out for material evaluation of fabricated TBCs. According to the results of material evaluation, the spray process is optimized for improving coating quality, and the proper raw materials are selected as a result of microstructural analysis. Especially, it is found that the durability and strain tolerance to thermal shock are remarkably increased by the gradation of TBCs and the improvement of graded TBC results from the fracture mechanism related to the vertical crack.

A CoNiCrAlY-hBN/Polyester material has recently been developed for clearance control applications in gas turbine compressors that use titanium alloy blades. While engine tests serve as the final evaluation of the coating performance, quality assurance laboratories and production shops would rely upon the more readily available coating hardness values to predict performance. This paper will focus on the reproducibility of coating macrohardness with a plasma spray process. It is shown that plasma spray parameters affect the hardness of CoNiCrAlY-hBN/Polyester coatings by changing the level of polyesters retained in the coating and the volume percentage of metallic matrix. The correlation between hardness, retained polyester level and microstructure of these coatings is captured in a coating hardness map from which desired microstructure and polyester entrapment are determined. Based on the understanding of the correlation between coating hardness and microstructural features, the use of additional criteria other than hardness such as retained polyester level and non-metallic portion of the coating is recommended in order to assure the quality of the coating more effectively.

Atmospheric plasma spraying (APS) is characterized by complex interactions between input, process and output variables. Process control relies heavily on human expert knowledge and experience. Process diagnostics can provide additional information to the operator and support cognitive processes in task execution. When using non-cascaded torch systems, significant plasma fluctuations occur, affecting the coating quality. High-frequency fluctuations can only be detected by suitable diagnostic systems and interpreted by experienced APS operators. In this study, the state of the plasma jet (area, fluctuation) is investigated depending on total plasma gas flow rate (50 vs. 65 l/min) and the H 2 content of plasma gases (17, 20 and 23 vol. %) using high-speed camera pictures. To evaluate plasma fluctuation effects, particle temperature and velocity as well as resulting coating properties (thickness and porosity) are determined for two ceramic systems. The results show that fluctuations of the plasma jet have a significant effect on the particle state and coating quality. The use of a high-speed camera to evaluate the stability of the plasma jet is an attractive method that, when properly integrated, has the potential to provide the human operator with important information to allow rapid assessment of input parameters or the condition of the plasma torch.

The development of thermal spray processes usually requires an analysis of the complex coating microstructure. In order to inspect critical areas of a coating, destructive testing methods such as the preparation of cross-sections are commonly used. In this work, the suitability of largely non-destructively measured polarisation curves for the quality assessment of thermal sprayed AISI 316L coatings is investigated. Therefore, a 3.5 % NaCl gel electrolyte was developed to prevent the corrosive medium from infiltrating the porous and micro-cracked microstructure characteristic for thermal sprayed coatings. In addition, a measuring cell based on the 3-electrode arrangement was designed to simplify the setup, reduce the measurement time and enable mobile measurements directly on the component surface at a later stage of development. The effects of process-related differences in the microstructure of HVAF and APS AISI 316L coatings on the polarisation curve was investigated by determining the corrosion current density. The microstructure of the AISI 316L coatings was analysed by optical microscope, SEM and EDS, focussing on the porosity and oxide content. The results clearly show that the potentiodynamic polarisation curves of the AISI 316L coatings differ significantly depending on the spray process used and microstructure created. Even small changes in the oxide content within a coating can be detected. Therefore, electrochemical measurement methods using gel electrolyte offer an interesting opportunity to evaluate the quality of thermal sprayed AISI 316L coatings in a largely non-destructive manner.

Thermal Barriers Coatings (TBC) are mass-produced in several industrial fields: aeronautic, automotive or energetic industries. All production requires the same constant level of fest and reproducible quality control at the lowest cost. The metallographic process is the primary way to evaluate thermally sprayed coatings but it must be both highly very repeatable and fast, especially when metallography is used to keep the production at a constant level. Therefore the management and the organization of a metallographic laboratory is of prime importance in order to reduce the cost and to provide a quality structure. The present approach to the whole chain of characterization is based on the user's point of view. Generally speaking, metallographic control of widely used parts often seems to be considered to be an uninteresting and obtuse subject, since it has been in practice for so long. Despite the lack of the prestige associated with the subject, optimization of an appraisal post can provide very concrete and more importantly profitable, results.

This study evaluates a new surface finishing process called laser-assisted turning. WC-CoCr coatings were produced by HVOF spraying and characterized based on surface morphology, microstructure, and friction and wear properties. The coatings were then treated using the new process and re-examined and tested. Surface roughness and hardness were significantly improved, although friction and wear properties were found to be inferior to those of WC-CoCr coatings finished by grinding and polishing.