Standard Guide for Nondestructive Examination of Metal Additively Manufactured Aerospace Parts After Build

Importancia y uso:

4.1 Metal parts made by additive manufacturing differ from their traditional metal counterparts made by forging, casting, or welding. Additive manufacturing produces layers melted or sintered on top of each other. The part’s shape is controlled by a computer as well as by the layers. The computer directs energy from a laser or electron beam onto a powder bed or wire input material. These processing approaches have the potential of creating flaws that are undesirable in the as-built or finished part. In general, processing parameter anomalies and disruptions during a build may induce such “flaws.” Flaws can also be introduced because of contaminants present in the input material.

4.2 Established NDT procedures such as those given in ASTM E07 standards are the basis for the NDT procedures discussed in this guide. These NDT procedures are used to inspect production parts before or after post-processing or finishing operations, or after receipt of finished parts by the end user prior to installation. The NDT procedures described in this guide are based on procedures developed for conventionally manufactured cast, wrought, or welded production parts.

4.3 Application of the NDT procedures discussed in this guide is intended to reduce the likelihood of material or component failure, thus mitigating or eliminating the attendant risks associated with loss of function, and possibly, the loss of ground support personnel, crew, or mission.

4.4 Input Materials—The input materials covered in this guide consist of, but are not limited to, ones made from aluminum alloys, titanium alloys, nickel-based alloys, cobalt-chromium alloys, and stainless steels. Input materials are either powders or wire.

Note 3: When electron beams are used, the beam couples effectively with any electrically conductive material, including aluminum and copper-based alloys.

4.4.1 Powders—High-quality powders required for AM process are produced by (1) plasma atomization, (2) inert gas atomization, or (3) centrifugal atomization using rotating electrodes (Fig. 1).

(A) Abbreviations used: … = unknown or not applicable, CAD = computer aided design, CMM = coordinate measuring machine, CT = computed tomography, DED = directed energy deposition, EBM = electron beam melting, ET = eddy current testing, EMF = electromagnetic frequency, HIP = hot isostatic pressing, IRT = irfrared thermography, LOF = lack of fusion, MET = optical metrology, PA = plasma arc, PBF = powder bed fusion, PCRT = process compensated resonance testing, PT = penetrant testing, SLM = selective laser melting, and UT = ultrasonic testing.(B) Portions of table courtesy of AMAZE FP7 project.(C) Discontinuities or indications detected by NDT that are not necessarily rejectable.(D) Due to rapidly quenching, which may also lead to metastable or nonequilibrium morphologies.(E) Issue during long builds.(F) ISO TC 261 JG59 N 237 Guide.(G) If surface or near surface.

Note 15: There are longstanding NDT standard flaw classes for welds and castings. In general, the defect classes for welded and cast parts differ from the flaw classes for AM parts.

4.9 Process-Flaw Correlation—Given the range of materials and processes encountered in metal additive manufacturing, the process origins of flaws are still being characterized. However, examples exist. For example, when the energy input is insufficient, successive scan tracks do not properly fuse together and flaws appear along the scan line. In L-PBF parts, incomplete wetting and balling effects associated with insufficient energy input have been shown to lead to pores or voids. In addition, EB-PBF parts can show large voids or cavities extending across several layers when the process parameters are not carefully chosen. Smaller spherical pores can also develop in EBM parts due to entrapment of gases originally present gas-atomized metal powders.

4.10 Flaw-Property Correlation—Parts with flaws, for example, porosity, LOF, skipped layers, stop/start flaws, inclusions, or excessive surface roughness, can exhibit degraded strength and fatigue properties compared with parts with fewer flaws. Furthermore, it is accepted practice to identify regions experiencing principle stresses before NDT is performed to assess the potential effect of any detected flaws in those regions. In addition to flaw type, size, and location, other flaw characteristics may be relevant, such as number, total volume, flaw/length (aspect ratio), orientation, and average nearest neighbor distance, and proximity to surfaces.

(A) Abbreviations used: DED = Directed Energy Deposition, HAZ = Heat Affected Zone, HIP = Hot Isostatic Pressing (A) Abbreviations used: … = not applicable, AE = Acoustic Emission, CR = Computed Radiography, CT = Computed Tomography, DR = Digital Radiology, ET = Eddy Current Testing, IRT = Infrared Thermography, LT = Leak Testing , MET = Metrology, MT = Magnetic Particle Testing, NR = Neutron Radiography, PCRT = Process Compensated Resonance Testing, PT = Penetrant Testing, RT = Radiographic Testing, UT = Ultrasonic Testing, and VT = Visual Testing.(B) Includes Digital Imaging.(C) Especially helpful when characterizing internal passageways or cavities (complex geometry parts) for underfill and overfill, or other internal features not accessible to MET, PT, or VT (including borescopy).(D) Applicable if on surface.(E) Radiographic methods are not optimal for detecting tight laminar features like cracking and LOF, which typically do not exhibit enough density change.(F) If large enough to cause a leak or pressure drop across the part.(G) Macroscopic cracks only.(H) Conventional neutron radiography (NR) allows determination of internal and external dimensions.(I) Pycnometry (Archimedes principle).(J) Density variations will only show up in imaged regions having equivalent thickness.(K) If inclusions are large enough and sufficient scattering contrast exists.(L) Residual stress can be assessed if resulting from surface post-processing (for example, peening).

Subcomité:

E07.10

Referida por:

E3353-22

Volúmen:

03.04

Número ICS:

49.035 (Components for aerospace construction)

Palabras clave:

additive manufacturing; computed tomography; defect; directed energy deposition; discontinuities; flaw; lack of fusion; laser scanning; nondestructive testing; optical metrology; photogrammetry; penetrant testing; porosity; powder bed fusion; process compensated resonance testing; radiographic testing; structured light; thermographic testing; ultrasonic testing; unconsolidated powder;