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Nondestructive Evaluation Program

Foundational Methodology for the Inspection and Qualification of Additive Manufactured Parts

Active Technology Project

Project Introduction

This multi-center activity investigates the correlation between nondestructive evaluation (NDE), mechanical testing, microstructure, and additive manufacturing (AM) process method. This will allow the effect of typical/naturally-occurring defects of known type, size and distribution on AM part performance to be determined. This investigation will include multiple AM materials (such as titanium, nickel-based and aluminum alloys) and AM fabrication process methods, including but not limited to direct metal laser sintering (DMLS) and electron beam melting (EBM). Results from this study will also be compared with those from conventionally formed (wrought and cast) materials of similar alloys.

Objectives

Perform a fundamental investigation correlating NDE data (in-process and post-process), mechanical test data, part microstructure, and AM process method, thus allowing the effect-of-defect to be determined for typical/naturally-occurring defects in AM parts. The defects interrogated by NDE often will be unique to AM, such that no severity of effect on performance may exist. This investigation includes multiple AM materials (such as titanium, nickel-based and aluminum alloys) and AM process methods. Emphasis is given to materials and processes favored by NASA, for example, Ti-6Al-4V and nickel alloy parts made by powder bed fusion (PBF) or wire-fed electron beam freeform fabrication (EBF3) methods. NDE is being used to select specimens for testing to failure, and then correlating the failure site back to the NDE results and subsequent fractography.

 

The second part of this work [WJM(TI1] utilizes a modular[WJM(TI2]  NDE physical reference standard to conduct a round-robin study of NDE methods suitable for complex AM components. This study would include both internal NASA NDE sources and outside entities and be conducted as a “request for information” (RFI). From this a recommendation for down selecting the most promising NDE methods to pursue for typical AM components based on defect characteristics, sample geometry and material properties can be made.

 

The ultimate goal will be to develop NDE protocols that will be used by NASA that are complementary to and augment the NDE section in the draft NASA Marshall Technical Standard Engineering and Quality Standard for Additively Manufactured Spaceflight Hardware. The NDE protocols so developed will give concise direction on how to perform NDE to qualify and certify AM parts for NASA use. This will facilitate the extension of applicable NASA requirements documents to AM hardware (for example, NASA-STD-5001 (Structural Design and Test Factors of Safety for Spaceflight Hardware), -5009 (Nondestructive Evaluation Requirements for Fracture-Critical Metallic Components), and -6016 (Standard Materials and Processes Requirements for Spacecraft).

 

Background

New methods for producing net shape and near net shape aerospace parts from AM methods have been developed in recent years. The potential for manufacturing complex parts from the AM processes that would otherwise require many subassemblies, require extensive machining operations, or just be impossible to machine, versus conventional manufacturing, is quite significant.

 

There are significant cost and time benefits to be gained from the AM process if it is used correctly, but there are many pitfalls due to unknowns and variations in the AM process. The material form coming out of these AM processes has uniquely different grain structure and flaw morphologies versus cast or wrought materials which will require a new understanding for how the various NDE methods will behave with it. Then to complicate the matter more, the highly complex and hidden geometries that can be formed with the AM process will make conventional NDE all the more challenging. The NDE Teams from the Marshall Space Flight Center (MSFC) and the Glenn Research Center (GRC) are working to build on and leverage recent fundamental and applied research efforts in the area of NDE for AM components. Both Centers have recently worked towards collecting preliminary NDE and materials data to help characterize natural flaws in the AM materials. The focus at GRC has been titanium-based EBM AM components while the focus at MSFC has been more on Inconel based SLM AM parts. The work at GRC has been focused on utilizing baseline NDE measurements with X-ray computed tomography (CT), penetrant, and ultrasonics prior to mechanical testing to understand the nature of failure sites during tests. The work done at MSFC has been focused on investigating the effects-of-defects and defect standard formation in SLM parts. Here samples were fabricated with trapped, un-fused, metal powder and small regions where the layers of powder were “skipped” during the fusing process. Defect standards as well as test parts were built and tested with standard NDE including penetrant, ultrasonics, radiography, eddy current as well as CT. The primary focus of the first phase of this work will be to establish fundamental relationships between processing, mechanical testing, materials characterization, and NDE. The second phase of this work will focus on understanding what NDE methods are best utilized for characterizing actual AM-produced components

 

Customers

SLS Engines, Commercial Crew, Space Station, DOD, AM Community, NDE Community.

 

Products

Handbook for creation of defects for NDE; A summary on effects-of-defects; Prioritized list of NDE methods that show the most promise for complex AM parts.

 

Milestones

Part 0: Determine metals, defects/artefacts, geometrical complexity, candidate NDE methods, and equipment build parameters for 1) NDE physical reference standards (universal NDE standard, slabs, rods, gage blocks, stepped wedges), and 2) NDE reference parts with seeded defects. Use in-house, industry and VCO consultation as needed. Issue Recommendations.

Part 1: Construction of test matrix; Fabricate/verify samples with a range of defects for mechanical testing, microstructural characterization and NDE characterization; Evaluate NDE capability; Perform materials testing on selected samples to see effect of defects; Report.

Part 2: Prepare a request for information solicitation to evaluate a complex AM part and submit; Collect responses and prepare a down select/priority plan; Send part out for testing; Collect the results and tabulate findings; Report.

 

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