The US Navy has adopted High-Pressure Cold Spray (HPCS) as a repair technique for corroded and worn components in their fleet of aircrafts, ships, and submarines. HPCS repairs are not only used for depositing corrosion and wear resistant coatings but is being successfully used for dimensional restoration in metal parts and components. By utilizing HPCS, the Navy ensures the longevity and reliability of critical components, even in harsh environments. Whether safeguarding against corrosion or restoring worn parts, HPCS is playing an increasingly critical role in maintaining operational readiness for the US Navy and other DOD agencies, as well as the commercial industry.

All companies involved in aviation industry face severe global competition. Thereby in particular maintenance, repair and overhaul (MRO) companies deal with difficult challenges for a modern production. Already today a clear trend for high flexibility, reduced process times and costs is visible. To face these challenges different options for thermal spraying processes will be presented. Thereby modern gun technologies and system concepts can achieve an up to 70% reduced total process time. However, by only optimizing hardware the needs of a modern production could not be fulfilled. Also established standards like quality management or development structures need to be adapted. For example the mostly used sample based quality management shows several disadvantages like time-delayed failure detection and a high rework rate. Here a well balanced concept based on the three pillars: particle monitoring, parameter monitoring and a reduced sample based quality management could achieve an efficient quality management with rework rates below 4%. Finally the positive aspects of modern Design of Experiment (DoE) strategies for coating development are presented. By using DoE times and efforts for developing could be reduced by 60%. A model based target value optimization could even enable a calculation of process parameters.

Cold spray is a reduced temperature, supersonic thermal spray process that is increasingly being used to perform repairs on high value components. In this case, a valve actuator internal bore sealing surface was repaired on an aluminum 6061 hydraulic valve body using high pressure cold spray. Corrosion damage to non-critical surfaces was also repaired, allowing the part to be returned to service. The VRC Gen III high-pressure cold spray system was used to deposit gas atomized 6061 aluminum powder. The internal bore surfaces were approximately 100 mm in diameter with a depth of nearly 200 mm, and were sprayed using a 45-degree nozzle 65 mm in length. The minimum required adhesion strength on critical surfaces was 69 MPa. The average adhesion strength was 71.4 MPa, with glue failures on ASTM C633 bond test specimens.

The ability to respond timely and cost effectively is bringing rapid manufacturing techniques into the mainstream production/repair arena. The Army can benefit from such technologies to avoid long lead times and high costs of procuring and inventorying replacement parts. But, a technology that offers versatility in terms of product size, cost and the ability to fabricate production components rapidly is yet to be available. This paper describes thermal spray technologies as applied to rapid manufacturing, part refurbishing and reengineering. A hybrid thermal spray system that can deposit a variety of materials with high throughput and density has been developed. Several generic materials that can meet the functional requirements of many parts and at the same time can be easily deposited by a thermal spray technique are discussed. An expert system software assisting the operator from CAD information, reverse engineering to part refurbishing is presented. Examples on the use of multiple schemes to remanufacture a part are also discussed. These schemes offer new avenues to fabricate replacement parts and/or salvage damaged parts and can benefit the Army considerably.

Cold spray additive manufacturing (CSAM) is an emerging process that has garnered significant attention from researchers due to its unique advantages. These include higher deposition rates, no need for a protective atmosphere, and the ability to connect or combine dissimilar materials. While CSAM allows for near-net-shape fabrication of workpieces, the accuracy and properties of the final products often fall short of user requirements. Furthermore, there is an urgent need to develop a generalized manufacturing strategy for workpieces with complex geometries. It appears that integrating various processes throughout the entire manufacturing workflow, from design to delivery, could address these challenges. However, few researchers have explored this area. To fill this gap, this study presents an integrated modular CSAM system designed for efficient and flexible workpiece fabrication. The system comprises two main components: software for modeling and simulation, and hardware for precise fabrication, each containing multiple modules. These modules do not operate independently but are coupled through direct or indirect decentralized and event-driven physical links. The system described in this paper offers a generalized strategy for precision manufacturing of workpieces using CSAM, potentially advancing the field and addressing current limitations in accuracy and versatility.

This paper discusses the ongoing development of a standard for manufacturing and testing thermal spray coatings used in the repair of aircraft engines. Excellent progress has been made in eliminating non-value added tests and in defining a system for preparing metallographic specimens and conducting microstructural evaluations. Paper includes a German-language abstract.

As an emerging additive manufacturing method, cold spray additive manufacturing (CSAM) has attracted more and more researchers’ attention due to its unique advantages. However, only a few researchers have studied the fabrication of complex structural components. Therefore, it is important to develop a general CSAM framework that is suitable for the fabrication of different shapes of workpieces. In particular, the choice for the optimal kinematic spraying parameters, the prediction of deposit evolution and the planning of spraying trajectory are the most basic and crucial. Different sub-modules are integrated in the proposed framework to solve these problems. In detail, the modeling methodology is used to obtain the optimal kinematic spraying parameters and to predict the deposit evolution in the simulation. Based on the feasible parameters, the trajectory planification methodology is used to generate the spraying trajectory for the workpiece being manufactured, especially the workpiece with complex structure. Finally, the simulation and experimental results of a fabrication for a workpiece with complex structure provide the developed system is reliable and effective. The framework developed in this paper can considered as a general tool for additive manufacturing of with complex structural workpieces in the CSAM.

The paper will describe a collaboration of the DoD Propulsion Environmental Working Group (PEWG), Oklahoma City Air Logistics Center (OC-ALC), Pratt & Whitney and Engelhard Corporation to qualify and transition High Velocity Oxy Fuel (HVOF) thermal spray of tungsten carbide coatings to replace electrolytic chrome plating for the repair of Pratt and Whitney (PWA) engines at the OC-ALC. This depot is the primary location for engine repair for the US Air Force. The paper details the engineering effort to qualify the HVOF tungsten carbide coating on PWA TF33 engine components as an precursor to qualifying the coatings for other military PWA engines. The paper also provides details of the transition of HVOF thermal spray technology into a new state-of-the-art production facility at the OC-ALC depot. The paper highlights a notably successful industry and government partnership to rapidly transition a world-class thermal spray capability into OC-ALC. The PEWG is a special management group that works with US military propulsion managers to educate/apprises government and industry collaborations of mature advanced pollutant free technologies and then facilitate the transition to full-scale production. Pratt and Whitney is the original equipment manufacturer of the TF33 engine and supplies other gas turbine engines to the Air Force and other military services. Engelhard Corporation is a surface and science company that develops technologies to improve customers’ products and processes. A Fortune 500 company, Engelhard is a world-leading provider of technologies for environmental, process, appearance, performance application and engineering solutions. Engelhard led the technology transition effort under contract to the PEWG. [This effort, as will be described in the paper, encompasses process engineering, coating qualification, spray parameter definition, tooling concepts, accelerated mission engine test support, inspection techniques, and production bed-down at the OCALC depot.]

Arc spray systems are increasingly used in the overhaul of aircraft engine components and auxiliary power units. The increasing use of arc spray over plasma for metallic coatings has created a demand for new wire approvals. The chemistry is already established as a powder and it is a matter of conversion to a wire and the arc spray process. The increasing popularity of the arc spray process is due to its superior bond strength and microstructure that exceed those of plasma. In one case, there is a two and one-half percent porosity requirement for the arc spray and up to 15% is allowed for plasma. This density approaches HVOF quality requirements. This paper will discuss some historical background of the process, what is approved and then move on to the new materials that are submitted for approval. Microstructures and bond strengths will be presented and some information about a proprietary method to solve a coating problem in the aircraft overhaul industry of long standing. The paper will also discuss new advances in arc spray systems and materials, which makes these systems amenable to replacing plasma sprayed coatings.

Recent developments of High-Velocity Air-Fuel (HVAF) spraying and blasting focused on a substantial increase of spray particles velocity. The efforts further improved coating quality, allowing deposition of metallic and carbide-base coatings non-permeable to gas at thickness as low as 40-50 micron. The coatings demonstrate low dissolved oxygen content, a favorable combination of high hardness and toughness. Coupled with the enhanced technological efficiency of modern HVAF equipment, this initiated not only the acceptance of HVAF technologies in established thermal spray markets in the oil and gas industry, but also the development and successful implementation of new coating applications. The examples are wear and corrosion resistant tungsten carbide-based coatings on hydraulics rods of dock cranes, corrosion resistant Ni-Cr-Mo-type coatings on vessels of sulfur removal equipment, tungsten carbide coatings on restriction grid plates and slide gates of catalyst towers, high-temperature erosion resistant chromium carbide- based coatings on thermowells and valve stems, wear and cavitation resistant Co-Cr-W-C-type and carbide coatings on housing wear rings and impeller hubs of high-temperature pumps.

Spurred on by the initial success of cold spray applications, a wide range of industrial sectors have since shown a tremendous interest in the youngest of the thermal spray processes. The forerunner, oxide-free copper coatings, paved the way for a variety of materials to be successfully sprayed at the Linde Technology Centre in Munich. At the same time, the hardware for cold spraying also underwent rapid development. This now means that new materials can be processed with the highest efficiency and quality possible, using lower-cost nitrogen rather than helium which is decidedly more expensive.

KLM Royal Dutch Airlines has the oldest Maintenance, Repair and Overhaul (MRO) shop for aircraft in the world (more than 80 years old). The company’s philosophy in all areas, including thermal spray, has always been to pursue the latest innovations and to maintain well-equipped facilities with state-of-the-art processes, equipment and materials for performing repairs. In the area of thermal spray, the latest procurement is a state-of-the-art unique cabinet with a high enthalpy plasma spray process. This new cabinet and new plasma spray process provides up-to-date technology for applying thermal spray coatings on aircraft engines. In this paper, experiences and the latest results obtained using this system to deposit various types of coatings used on aircraft will be reported.

Several attempts have been made in the past to compare the coating costs associated with different processes. These have been based normally on various process related assumptions. The comparisons have typically been biased by the views and objectives of the presenters. A realistic comparison of the process costs needs to be based on the actual production methods and the historical data. This paper presents the comparisons of the Vacuum Plasma process with two versions of the HVOF process. Both small and large part geometries are considered as well as part complexity. The cost data will be presented as an actual cost per part to coat, including both operating costs and amortized capital costs. This method is preferred over the theoretical calculation of the cost per pound of material sprayed. The latter method requires a number of assumptions and does not consider the limitations of production cycles and material handling.

Laser-assisted cold-spray has been recognized for over a decade as a technique capable of depositing high quality coatings. By laser heating (and hence softening) the surface being coated, deposition can occur at particle velocities lower than those normally associated with the cold spray process. This can be used to increase deposition rate. However, it can also be used to facilitate the deposition of higher hardness material combinations, normally more out of the reach of the conventional cold spray process. Laser heating can also reduce the requirements of the process on gas usage and gas heating for a given combination, making it more cost-effective. In the work reported below, the capability of a novel co-axially laser-assisted system (COLA) to deposit higher hardness materials, relevant to a range of different industrial applications, has been evaluated. This system can be retrofitted to conventional cold spray equipment.

With the vast array of coating technologies and materials available in the marketplace, matching the best coating to an application is far from a trivial task. There is a tendency on the part of vendors, for example, to put forward any hard coating as a chrome replacement or any corrosion-resistant coating as an alternative to cadmium. At the same time users often attempt to shoehorn the coatings with which they are most familiar into applications for which they are not well-suited. This paper will discuss how best to match the application to the best technology and material, considering all the critical requirements of fit, form and function, with particular reference to alternatives for chrome and cadmium plating.

For many years coatings have been successfully applied to aerospace engine components to improve life and performance. The key success areas have been in thermal barrier coatings, clearance control, oxidation/hot corrosion and wear coatings. Today, design engineers in the industrial gas turbine sector have leveraged the “aerospace” technology into the power generation industry. This paper gives a general overview of key coatings used in the compressor and turbine sections. Design requirements will be reviewed and compared between aerospace and power generation coatings. Application process improvement areas will also be discussed as a method of reducing component cost. Therefore, the total solution will be more reproducible, cost effective coatings that add value. This will result in engineered components that operate at higher temperatures and/or last for longer periods of time.

This work focuses on the laser cladding process and the behavior or interaction between the powder particles and the laser beam, specifically examining how various process parameters might affect the creation of melt pool formations. The experiment focused on examining the influence of laser intensity and other important factors on the amount of metal in the substrate of 316L stainless steel, particularly while utilizing Inconel 625 powder. The study was conducted by utilizing cross-sectional images and quantifying the ratio of areas of the melted substrate material across a sliced cross-sectional area. The study also investigated the influence of recirculation patterns resulting from the Marangoni convection force on the formation of the melt region. The study's results indicate that a low powder feed rate is preferable, which in this study was 5 g/min, and provides better results with a symmetrical and profound melt profile. The melt shifts to asymmetrical profiles when the feed rate increases significantly over this value. The primary cause of this phenomenon is attributed to the Marangoni forces and the momentum transfer generated by the powder jets. The investigation also emphasizes the complex interplay among the process factors and highlights the crucial role of laser source power in triggering a fast escalation in the volume of melted material. In addition, the study supports the idea that maintaining the laser energy input as a constant helps to create a consistency in the total melt area even when the cladding speed is increased.

Stripping systems for thermal spray coatings tend to use many hazardous acids which require critical safety procedures and produce heavy volumes of environmentally unfriendly waste streams. A new technology, filed under application numbers 2009/0120804A1 and 2009/0229636A1, and additionally covered under U.S. patent numbers 8262870 and 8377324 has been created using a very safe and environmentally friendly percarbonate based chemical system with minimal DC rectified voltage. It was successfully qualified at Tinker Air Force Base and is currently in production use throughout the facility. It has safely stripped WCCo and CrC-NiCr coatings such as WCCo and CrC-NiCr from Ti 6-4 and IN718 substrates showing minimal stock loss in 48 hr exposure testing. Many lessons were learned during this qualification process which will be shared and documented. Both plasma and HVOF coatings can be stripped with this process in the pH 10-12 range. The system can also be combined with a refining system that purifies the waste water and condenses the coating sludge into a condensed volume, eliminating the tremendous volume of waste chemicals. Numerous case studies and actual stripping data will also be presented and discussed.

This paper provides best practices along with a detailed example of how to effectively meet thermal spray training needs. It discusses the importance of giving students hands-on experience with real equipment and the many and varied problems they are likely to encounter with its use. It also discusses the value of allowing students to learn by exposing them to improper techniques, flawed approaches, and incorrect equipment repairs.

The desire to enhance the performance and efficiency of gas turbine engines has led to higher engine operating temperatures. To accommodate these higher temperatures, new superalloys and material systems have been developed, along with novel cooling techniques. However, with operating temperatures exceeding the acceptable maximum metal temperatures, thermal barrier coatings (TBC) are used for underlying metal surface protection. This paper reviews the art and technology of air plasma sprayed TBC coatings onto hot section components from a job shop perspective. The specification for such coatings and its practical implications are discussed. The issues in applying such coatings will be discussed, along with references to manufacturing issues on the shop floor. The difficulties inherent m applying a line-of-sight coating to complex geometry will be discussed, with particular reference to automated or robotic spraying. The utility of using a design-of-experiment approach to satisfy the user will be reviewed. Data will be presented to show the economic impact of process optimization.