WP8: in-situ and ex-situ repairs of aeronautical components: validation

Lead by: AVIO
Participating partners: POLIMI, VN, TWI, NAU KHAI, METALOGIC, EADS, EADS-CASA, LPW, IMPACT, IBERIA
Duration: July 2015 – October 2016 (M26-M41)

Overview: Challenges and current SoA

The main purpose of WP8 is to define the validation approach of the Cold Spray repair process to allow the application to aeronautical components. This involve the identification of the main engineering and quality requirements to be detailed in guidelines and acceptance standard, and the way to verify the conformity of the cold spray deposition with respect to the established requirements. The validation approach could be quite similar to the one used for the current thermal spray deposition processes, taking care of the peculiarity of the Cold Spray deposition.

Main Objectives

Like WP7, WP8 will follow the initial investigations of the previous WPs in order to in turn validate the performed repairs. WP8 will also care to collect and define the methodologies developed in CORSAIR project in a structured set of guidelines and standards, including guidelines for assessing coating quality when using the portable CS plant.

Related Activities

Task 1: validation of repaired parts

SubTask 1.1: Visual Inspection

The component will be firstly submitted to visual inspection, first by the specific cold spray repair performer then by the specific aeronautic company producing that component. The thickness homogeneity as well the presence of non-coated zones or macro-defects will be investigated.

SubTask 1.2: FPI and X-Ray tests

FPI inspection and X-ray inspection will be carried out by the aeronautic companies following standard procedures employed for validation of repaired components.

SubTask 1.3: Structural and Microstructural validation

Structural (depending on materials and component) and Microstructural analysis will be carried out in parallel by aeronautic companies (if possible) and specific RTD site performing the repair. The quality of interface between base material and deposited coatings will be verified as well the presence grain size and particle deformation, the presence of porosity and oxidation. EDX analysis will be carried out in order to emphasize the contaminations. Microhardness tests will be also performed.

SubTask 1.4: Adhesion

Adhesion will be evaluated by means of ASTM-C633. Test will be performed on various components.

SubTask 1.5: Further analyses

Further analysis, mechanical, chemical or thermal depending on deposited materials, component and specific end-use, could be defined and carried out according to the procedures and involved partners defined in WP5 and WP6. This will allow assessing the feasibility of thermography for field inspection following in-situ reparations of the selected components.

Task 2: Guidelines and standards

Subtask 2.1 – Guidelines for Cold Spray implementation as maintenance operation

The relevant results gained from the previously described tasks will be properly collected and organized, in order to develop a reliable and repeatable methodology for the application of Cold Spray in industrial repairing of airplane parts and aeronautical components. This will be benchmarked against the only current Cold Spray manufacturing standard (MIL-Std-3021 Materials Deposition, Cold Spray, Department of Defense Manufacturing Process Standard (Metric)) with a view to providing the basis for a draft EU standard. The role of aeronautic companies will be fundamental to drive the definition of the new guidelines for cold spray, starting from the currently employed and consolidated procedures in similar processes (i.e. plasma spray, HVOF).

SubTask 2.2 – Guideline for experimental technique designed for assessing the results of the coating

Reparation procedures for the proper control of Cold Spray repairs will be defined. These will consist of reliable standard methodologies meant to allow the process operators to control the process efficiency by means of determined parameters, which have proved to be linked to the process quality (e.g. XRD residual stress measurements, grain size measurements, SEM observations, roughness, corrosion resistance, etc).

Task 2.3 – Guideline for experimental technique designed for assessing the result of the coating

Documentation of guidelines for an end user to effectively apply the numerical models will be provided. A step-by-step help procedures will be given, demonstrating ways to tackle a model problem using the FE codes developed in WP2.

Task 3: Characterisation of deposited coatings obtained with innovative systems and nozzle and comparison with coatings obtained with standard commercial systems

Subtask 3.1: Preliminary basic characterization of coatings deposited with the new Portable Unit and comparison to coatings obtained using a steady-system

Preliminary physical and mechanical characterization of the samples will take place involving standard testing procedures as well as comparison against the properties of coatings obtained with a state-of-the-art, high pressure, mechanised Cold Spray system.

Bond strength, metallurgical analysis (porosity, substrate-coating interface quality) as well as corrosion and oxidation resistance will be studied and used as the main screening tests to assess the effect of cold-sprayed process parameters on the different materials deposited in the various substrates.

Samples passing previously defined quality criteria will be further characterized in terms of their corrosion resistance. The partners will realize a comparison with literature data in terms of corrosion and oxidation resistance as well as with respect to cold-sprayed samples using stationary Cold Spray plants. Optical microscopy (OM), X-ray diffraction (XRD) and different surface analysis techniques such as SEM coupled with EDX, shall be used in order to characterize the surface and in depth cold deposited coatings in an attend to correlate corrosion performance with coating features and Cold Spray processing parameters. The RTD partners involved in the characterization process above will be in a strong collaboration and interaction for receiving feedback devoted to optimise the design procedure.

Subtask 3.2: Preliminary basic characterization of deposited coatings with new nozzles on specific components and specimens and comparison to coatings obtained using the standard nozzles

Preliminary physical and mechanical characterization of the samples will take place involving standard testing procedures. These will be also compared against the properties of coatings obtained with a state-of-the-art, high pressure, mechanised Cold Spray system operating commercial nozzles. Basic characterization will include geometrical and metallurgical (morphology, microstructure, porosity) features, as well as cohesion and adhesion following TCT and ASTM-C633. Finally, the wear performance of these coatings should be compared with those processed using a steady cold spray system. The RTD and industrial partners involved will be in a strong collaboration and interaction for receiving feedback devoted to optimise the design procedure the and repair requirements.

Expected Results beyond the SoA

WP8 will ultimately result in validation of repaired parts by inspection and laboratory characterization and definition of Repair Components and Procedures which could be adopted in aeronautics. All aeronautical partners will collaborate to define the components and procedures charts. The procedures will be defined for the components considered and will be kept confidential. Additionally, cold spray procedures will be defined in general for application in aeronautics and the results will be disseminated to the public. WP8 will also allow the definition of Guidelines to implement cold spray as maintenance technique (reparation procedure) for each material/component considered. Definition of Guidelines for validating cold spray as a maintenance technique (validation procedure) for each material/component will be also be realized.

Progress

July 2015-February 2016 (M26-M33)

The main deposition parameters to be used for the Cold Spray repairs of aeronautical components have been identified, taking into account the powder characteristics, surface preparation, base materials, geometries of the areas to be repaired and coating performances. The requirements for the evaluation of the repaired components have also been defined. The next step will be the repair of representative components and their evaluation in terms of NDT, Structural and Microstructural examination, mechanical properties and surface protective treatments.

March 2016 – May 2016 (M34-M36)

The representative components to be repaired by Cold Spray have been selected. These are 357 Aluminum alloy casting having bearing seat diameters to be dimensionally recovered. The surface preparation and the deposition parameters to be used for the Cold Spray repair, the powder characteristics, including the powder size distribution, and the powder supplier have been defined. The activities related to the masking tooling, the support fixtures and to the robot part program are in progress. Two additional components have been sent to the partner in charge of the cold spray deposition to be specifically used to evaluate the tooling and fixture capability, and to verify the first deposition results. The repair of the representative components and their evaluation in terms of NDT, Structural and Microstructural examination, mechanical properties and surface protective treatments (anodizing) are expected in the next months.


 

The activities related to the CORSAIR research are being organized in the following Work Packages (WPs):