ASTM E3166-20e1

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
ϵ1
Designation: E3166 − 20
Standard Guide for
Nondestructive Examination of Metal Additively
Manufactured Aerospace Parts After Build
This standard is issued under the fixed designation E3166; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—The caption for Fig. 10 was editorially corrected in August 2020.
1. Scope Section9),penetranttesting(PT,Section10),processcompen-
sated resonance testing (PCRT, Section 11), radiographic
1.1 This guide discusses the use of established and emerg-
testing (RT, Section 12), infrared thermography (IRT, Section
ing nondestructive testing (NDT) procedures used to inspect
13), and ultrasonic testing (UT, Section 14). Other NDT
metal parts made by additive manufacturing (AM).
procedures such as leak testing (LT) and magnetic particle
1.2 The NDT procedures covered produce data related to
testing (MT), which have known utility for inspection of AM
andaffectedbymicrostructure,partgeometry,partcomplexity,
parts, are not covered in this guide.
surface finish, and the different AM processes used.
1.9 Practicesandguidanceforin-processmonitoringduring
1.3 The parts tested by the procedures covered in this guide
the build, including guidance on sensor selection and in-
are used in aerospace applications; therefore, the inspection
process quality assurance, are not covered in this guide.
requirements for discontinuities and inspection points in gen-
1.10 This guide is based largely on established procedures
eral are different and more stringent than for materials and
under the jurisdiction of ASTM Committee E07 on Nonde-
components used in non-aerospace applications.
structive Testing and is the direct responsibility of the appro-
1.4 Themetalmaterialsunderconsiderationinclude,butare
priate subcommittee therein.
not limited to, aluminum alloys, titanium alloys, nickel-based
1.11 This guide does not recommend a specific course of
alloys, cobalt-chromium alloys, and stainless steels.
action for application of NDT to AM parts. It is intended to
1.5 The manufacturing processes considered use powder
increase the awareness of established NDT procedures from
and wire feedstock, and laser or electron energy sources.
the NDT perspective.
Specific powder bed fusion (PBF) and directed energy depo-
1.12 Recommendationsaboutthecontrolofinputmaterials,
sition (DED) processes are discussed.
process equipment calibration, manufacturing processes, and
1.6 This guide discusses NDT of parts after they have been
post-processing are beyond the scope of this guide and are
fabricated. Parts will exist in one of three possible states: (1)
under the jurisdiction of ASTM Committee F42 on Additive
raw, as-built parts before post-processing (heat treating, hot
Manufacturing Technologies. Standards under the jurisdiction
isostatic pressing, machining, etc.), (2) intermediately ma-
ofASTM F42 or equivalent are followed whenever possible to
chined parts, or (3) finished parts after all post-processing is
ensure reproducible parts suitable for NDT are made.
completed.
1.13 Recommendations about the inspection requirements
1.7 TheNDTproceduresdiscussedinthisguideareusedby
and management of fracture critical AM parts are beyond the
cognizant engineering organizations to detect both surface and
scope of this guide. Recommendations on fatigue, fracture
volumetricflawsinas-built(raw)andpost-processed(finished)
mechanics, and fracture control are found in appropriate end
parts.
user requirements documents, and in standards under the
jurisdictionofASTMCommitteeE08onFatigueandFracture.
1.8 The NDT procedures discussed in this guide are com-
puted tomography (CT, Section 7, including microfocus CT),
NOTE 1—To determine the deformation and fatigue properties of metal
eddy current testing (ET, Section 8), optical metrology (MET, parts made by additive manufacturing using destructive tests, consult
Guide F3122.
NOTE 2—To quantify the risks associated with fracture critical AM
parts, it is incumbent upon the structural assessment community, such as
This guide is under the jurisdiction ofASTM Committee E07 on Nondestruc-
ASTM Committee E08 on Fatigue and Fracture, to define critical initial
tiveTesting and is the direct responsibility of Subcommittee E07.10 on Specialized
flaw sizes (CIFS) for the part to define the objectives of the NDT.
NDT Methods.
1.14 This guide does not specify accept-reject criteria used
Current edition approved Feb. 1, 2020. Published July 2020. DOI: 10.1520/
E3166-20E01. in procurement or as a means for approval of AM parts for
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E3166 − 20
service.Anyaccept-rejectcriteriaaregivensolelyforpurposes E1004Test Method for Determining Electrical Conductivity
of illustration and comparison. Using the Electromagnetic (Eddy Current) Method
E1025 Practice for Design, Manufacture, and Material
1.15 Units—The values stated in SI units are to be regarded
Grouping Classification of Hole-Type Image Quality In-
as standard. The values given in parentheses after SI units are
dicators (IQI) Used for Radiography
providedforinformationonlyandarenotconsideredstandard.
E1030Practice for Radiographic Examination of Metallic
1.16 This standard does not purport to address all of the
Castings
safety concerns, if any, associated with its use. It is the
E1032PracticeforRadiographicExaminationofWeldments
responsibility of the user of this standard to establish appro-
Using Industrial X-Ray Film
priate safety, health, and environmental practices and deter-
E1158Guide for Material Selection and Fabrication of
mine the applicability of regulatory limitations prior to use.
Reference Blocks for the Pulsed Longitudinal Wave Ul-
1.17 This international standard was developed in accor-
trasonic Testing of Metal and Metal Alloy Production
dance with internationally recognized principles on standard- 3
Material (Withdrawn 2019)
ization established in the Decision on Principles for the
E1065Practice for Evaluating Characteristics of Ultrasonic
Development of International Standards, Guides and Recom-
Search Units
mendations issued by the World Trade Organization Technical
E1209Practice for Fluorescent Liquid Penetrant Testing
Barriers to Trade (TBT) Committee.
Using the Water-Washable Process
E1255Practice for Radioscopy
2. Referenced Documents
E1316Terminology for Nondestructive Examinations
2.1 ASTM Standards:
E1416Practice for Radioscopic Examination of Weldments
E11Specification forWovenWireTest Sieve Cloth andTest
E1417Practice for Liquid Penetrant Testing
Sieves
E1441Guide for Computed Tomography (CT)
E94/E94MGuide for Radiographic Examination Using In-
E1475Guide for Data Fields for Computerized Transfer of
dustrial Radiographic Film
Digital Radiological Examination Data
E114Practice for Ultrasonic Pulse-Echo Straight-Beam
E1570Practice for Fan Beam Computed Tomographic (CT)
Contact Testing
Examination
E215PracticeforStandardizingEquipmentandElectromag-
E1695Test Method for Measurement of Computed Tomog-
netic Examination of Seamless Aluminum-Alloy Tube
raphy (CT) System Performance
E243PracticeforElectromagnetic(EddyCurrent)Examina-
E1742Practice for Radiographic Examination
tion of Copper and Copper-Alloy Tubes
E1817Practice for Controlling Quality of Radiological Ex-
E317PracticeforEvaluatingPerformanceCharacteristicsof
amination by Using Representative Quality Indicators
Ultrasonic Pulse-Echo Testing Instruments and Systems
(RQIs)
without the Use of Electronic Measurement Instruments
E1901Guide for Detection and Evaluation of Discontinui-
E426PracticeforElectromagnetic(EddyCurrent)Examina-
ties by Contact Pulse-Echo Straight-Beam Ultrasonic
tion of Seamless and Welded Tubular Products, Titanium,
Methods
Austenitic Stainless Steel and Similar Alloys
E1935Test Method for Calibrating and Measuring CT
E494Practice for Measuring Ultrasonic Velocity in Materi-
Density
als
E2001Guide for Resonant Ultrasound Spectroscopy for
E543Specification forAgencies Performing Nondestructive
Defect Detection in Both Metallic and Non-metallic Parts
Testing
E2007Guide for Computed Radiography
E571PracticeforElectromagnetic(Eddy-Current)Examina-
E2033Practice for Radiographic Examination Using Com-
tion of Nickel and Nickel Alloy Tubular Products
puted Radiography (Photostimulable Luminescence
E587Practice for Ultrasonic Angle-Beam Contact Testing
Method)
E664/E664MPractice for the Measurement of theApparent
E2104Practice for Radiographic Examination of Advanced
Attenuation of Longitudinal Ultrasonic Waves by Immer-
Aero and Turbine Materials and Components
sion Method
E2338Practice for Characterization of Coatings Using Con-
E747Practice for Design, Manufacture and Material Group-
formable Eddy Current Sensors without Coating Refer-
ing Classification of Wire Image Quality Indicators (IQI)
ence Standards
Used for Radiology
E2339Practice for Digital Imaging and Communication in
E797/E797MPractice for Measuring Thickness by Manual
Nondestructive Evaluation (DICONDE)
Ultrasonic Pulse-Echo Contact Method
E2373/E2373MPractice for Use of the Ultrasonic Time of
E1001PracticeforDetectionandEvaluationofDiscontinui-
Flight Diffraction (TOFD) Technique
ties by the Immersed Pulse-Echo Ultrasonic Method
E2375Practice for Ultrasonic Testing of Wrought Products
Using Longitudinal Waves
E2445Practice for Performance Evaluation and Long-Term
Stability of Computed Radiography Systems
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
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E3166 − 20
E2446Practice for Manufacturing Characterization of Com- 2.4 ASNT Standard and Practice:
puted Radiography Systems ASNT CP-189Standard for Qualification and Certification
of Nondestructive Testing Personnel
E2491Guide for Evaluating Performance Characteristics of
SNT-TC-1A Recommended Practice for Nondestructive
Phased-ArrayUltrasonicTestingInstrumentsandSystems
Testing Personnel Qualification and Certification
E2534PracticeforProcessCompensatedResonanceTesting
2.5 AWS Standard:
Via Swept Sine Input for Metallic and Non-Metallic Parts
AWS D17.1Specification for Fusion Welding of Aerospace
E2597Practice for Manufacturing Characterization of Digi-
Application
tal Detector Arrays
E2698Practice for Radiographic Examination Using Digital 2.6 EN Documents:
Detector Arrays EN 4179Aerospace Series—Qualification and Approval of
Personnel for Non-Destructive Testing
E2736Guide for Digital Detector Array Radiography
EN 15708-2 Non Destructive Testing—Radiation
E2737Practice for Digital Detector Array Performance
Methods—Computed Tomography—Part 2: Principle,
Evaluation and Long-Term Stability
Equipment and Samples
E2767Practice for Digital Imaging and Communication in
EN 15708-3 Non Destructive Testing—Radiation
Nondestructive Evaluation (DICONDE) for X-ray Com-
Methods—Computed Tomography—Part 3: Operation
puted Tomography (CT) Test Methods
and Interpretation
E2862Practice for Probability of Detection Analysis for
EN 15708-4 Non Destructive Testing—Radiation
Hit/Miss Data
Methods—Computed Tomography—Part 4: Qualification
E2884Guide for Eddy Current Testing of Electrically Con-
EN 60825-1Safety of Laser Products. Equipment Classifi-
ducting Materials Using Conformable Sensor Arrays
cation and Requirements
E2982Guide for Nondestructive Testing of Thin-Walled
2.7 Federal Standards:
MetallicLinersinFilament-WoundPressureVesselsUsed
10 CFR 20Standards for Protection Against Radiation
in Aerospace Applications
21 CFR 1020.40Cabinet X-ray Systems
E3022Practice for Measurement of Emission Characteris-
21 CFR 1040.10Laser Products
tics and Requirements for LED UV-A Lamps Used in
21 CFR 1040.11Specific Purpose Laser Products
Fluorescent Penetrant and Magnetic Particle Testing
29 CFR 1910.1096Occupational Safety and Health Stan-
E3023Practice for Probability of Detection Analysis for â
dards
Versus a Data
2.8 ISO Standard:
E3081Practice for Outlier Screening Using Process Com-
ISO 17296-2 Additive Manufacturing—General
pensated Resonance Testing via Swept Sine Input for
Principles—Part 2: Overview of Process Categories and
Metallic and Non-Metallic Parts
Feedstock
F2971Practice for Reporting Data for Test Specimens Pre-
2.9 MIL Documents:
pared by Additive Manufacturing
MIL-HDBK-1823Nondestructive Evaluation System Reli-
F3122Guide for Evaluating Mechanical Properties of Metal
ability Assessment
Materials Made via Additive Manufacturing Processes
MIL-STD-1907Inspection, Liquid Penetrant and Magnetic
F3187Guide for Directed Energy Deposition of Metals
Particle, Soundness Requirements for Materials, Parts,
ISO/ASTM 52900Terminology forAdditive Manufacturing
and Weldments
Technologies 12
2.10 NASA Standards:
ISO/ASTM DTR 52905Additive Manufacturing—General
NASA-STD-5009NASA Technical Standard, Nondestruc-
Principles—Non-destructive Testing of Additive Manu-
tive Evaluation Requirements for Fracture Critical Metal-
factured Products
lic Components
ISO/ASTM 52921 Terminology for Additive
Manufacturing—Coordinate Systems and Test Method-
ologies
AvailablefromAmericanSocietyforNondestructiveTesting(ASNT),P.O.Box
28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
2.2 AIA Standard:
Available from American Welding Society (AWS), 8669 NW 36 St., #130,
NAS 410NAS Certification & Qualification of Nondestruc-
Miami, FL 33166-6672, http://pubs.aws.org/.
Available from British Standards Institution (BSI), 389 Chiswick High Rd.,
tive Test Personnel, Revision 4, 2014
London W4 4AL, U.K., http://www.bsigroup.com.
2.3 ANSI Standard: Published by the Center for Devices and Radiological Health (CDRH) of the
Food and Drug Administration (FDA); available from Government Printing Office
ANSI, Z136.1-2000American National Standard for Safe
Superintendent of Documents, 732 N. Capitol St., NW, Mail Stop: SDE,
Use of Lasers
Washington, DC 20401.
Available from International Organization for Standardization (ISO), ISO
Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
Geneva, Switzerland, http://www.iso.org.
4 11
Available from Aerospace Industries Association (AIA), 1000 Wilson Blvd., AvailablefromStandardizationDocumentsOrderDesk,Bldg4SectionD,700
Suite 1700, Arlington, VA 22209, http://www.aia-aerospace.org. Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
5 12
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St., Available from the NASATechnical Standards System at the NASAwebsite,
4th Floor, New York, NY 10036, http://www.ansi.org. www.standards.nasa.gov.
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E3166 − 20
MSFC-STD-3716Standard for Additively Manufactured 3.3.4.1 Discussion—Types of flaws (not necessarily reject-
Spaceflight Hardware by Laser Powder Bed Fusion in able) specific to additive manufacturing include porosity/voids
Metal (isolated or cluster, surface or deeply embedded), lack of
MSFC-SPEC-3717Specification for Control and Qualifica- fusion, layer discontinuities (planar or linear), across-layer
tion of Laser Powder Bed Fusion Metallurgical Processes discontinuities,start-stoperrors,inclusions,layershifts,under/
over-melted material, metastable microstructures, residual
2.11 NBS Handbook:
stress, and poor dimensional accuracy.
114General Safety Standard for Installations Using Non-
3.4 Definitions of Terms Specific to This Standard:
Medical X-ray and Sealed GammaRay Sources, Energies
3.4.1 as-built, adj—refers to the state of the manufactured
up to 10 MeV
14 part before any post-processing, except where removal from a
2.12 SAE Standards:
base plate is necessary, or powder removal or support removal
AMS 2644Inspection Material, Penetrant
is required.
AMS 2175Castings, Classification and Inspection of
3.4.2 aspect ratio, n—the diameter to depth ratio of a flaw.
2.13 USAF Document:
AFRL-RX-WP-TR-2014-0162 America Makes: National
3.4.2.1 Discussion—For irregularly shaped flaws, diameter
Additive Manufacturing Innovation Institute (NAMII)
refers to the minor axis of an equivalent rectangle that
Project 1: Nondestructive Evaluation (NDE) of Complex
approximates the flaw shape and area.
Metallic Additive Manufactured (AM) Structures
3.4.3 crack, n—separation of material which may be inter-
2.14 VDI Document:
granularortransgranularinmetals;inseverecases,itcanresult
VDI/VDE 2630Various Parts, Computed Tomography in
in 2-D (planar) separation (delamination) between adjacent
Dimensional Measurement—Fundamentals and Defini-
build layers.
tions
3.4.3.1 Discussion—Cracks are caused by temperature dif-
ferences during melting or sintering, or relief of residual
3. Terminology
stresses upon cooling, and can be manifested at the micro-
3.1 Abbreviations—The following abbreviations are ad-
scopic level (hot tears) to macroscopic level (delamination).
opted in this guide: Computed Tomography (CT), Eddy Cur-
3.4.4 directed energy deposition (DED), n—an additive
rentTesting(ET),OpticalMetrology(MET),PenetrantTesting
manufacturingprocessinwhichfocusedthermalenergyisused
(PT), Process Compensated Resonance Testing (PCRT), Ra-
to fuse materials by melting as they are being deposited.
diographic Testing (RT), Infrared Thermography (IRT), and
3.4.4.1 Discussion—“Focused thermal energy” means that
Ultrasonic Testing (UT).
an energy source (for example, laser, electron beam, or plasma
3.2 Order of Precedence—In order of precedence, the fol-
arc) is focused to melt the materials being deposited.
lowing terminologies apply:
3.4.5 hit, n—an existing discontinuity that is detected as a
3.2.1 For terminology related to NDT, use Terminology
find during NDT.
E1316.
3.4.6 inclusion, n—foreign material, either non-metallic or
3.2.2 For terminology related to AM, use ISO/ASTM Ter-
metallic, incorporated into the deposited material.
minology 52900.
3.2.3 For terminology related to powder metallurgy, includ-
3.4.6.1 Discussion—Inclusions are typically oxides,
ing powder, powder types, powder additives, powder evalua-
nitrides, hydrides, carbides, or a combination thereof and may
tion procedures and powder processing techniques, use Prac-
or may not have some coherency with the surrounding mate-
tice E243.
rial.
3.3 Definitions:
3.4.7 lack of fusion (LOF), n—a type of process-induced
3.3.1 cognizant engineering organization, n—see Terminol-
porosity, in which the powder or wire feedstock is not fully
ogy E1316.
melted or fused onto the previously deposited substrate.
3.3.2 defect, n—see Terminology E1316.
3.4.7.1 Discussion—In PBF, this type of flaw can be an
empty cavity, or contain unmelted or partially fused powder,
3.3.2.1 Discussion—Defects do not meet specified accep-
referred to as unconsolidated powder. LOF typically occurs in
tance criteria and are rejectable.
the bulk, making its detection difficult. Like voids, LOF can
3.3.3 discontinuity, n—see Terminology E1316.
occur across single (horizontal LOF) or multiple layers (verti-
3.3.4 flaw, n—see Terminology E1316.
cal LOF).
3.4.8 miss, n—an existing discontinuity that is not detected
during NDT, whether due to the inspection system or human
Available from the United States Department of Commerce, National Bureau
factors.
of Standards.
Available from SAE International (SAE), 400 Commonwealth Dr.,
3.4.9 near net shape, n—condition where the parts require
Warrendale, PA 15096, http://www.sae.org.
little post-processing to meet dimensional tolerance.
Available from Air Force Research Laboratory, Materials and Manufacturing
Directorate, Wright-PattersonAir Force Base, OH 45433-7750 (Air Force Materiel
3.4.10 poor dimensional accuracy, n—physical measure-
Command, United States Air Force).
ments of geometrical features that do not meet engineering
AvailablefromVereinDeutscherIngenieure(VDI),Postfach1139,Dusseldorf
1, Germany 4000. drawing, leading to an out-of-tolerance part.
ϵ1
E3166 − 20
3.4.10.1 Discussion—This type of flaw is caused by stair distinctfromintentionallyaddedopencellsthatreduceweight.
stepping, relief of residual stresses and associated warping, Voids cause a part to be less than fully dense.
rapid contraction during cooling after fusion, or sagging under 3.5 Symbols:
gravity of unsupported areas with vertical overhang or down-
3.5.1 a—the physical dimension of a discontinuity, flaw, or
ward facing surfaces during build.
target—can be its depth, surface length, or diameter of a
3.4.11 porosity, n—see ISO/ASTM Terminology 52900.
circulardiscontinuity,orradiusofsemi-circularorcornercrack
having the same cross-sectional area.
3.4.12 porosity (gas), n—voids that are spherical or faceted
in shape; with sufficient sources of gaseous species, may be
3.5.2 a —the discontinuity size that can be detected with
p/c
intermittent within the deposit or elongated, interconnected, or
probability p with a statistical confidence level of c.
chained due to the moving solidification front.
4. Significance and Use
3.4.12.1 Discussion—Gas porosity is caused by absorption/
desorption of gaseous species (nitrogen, oxygen) during
4.1 Metal parts made by additive manufacturing differ from
solidification, or volatile contaminants (moisture or hydrocar-
theirtraditionalmetalcounterpartsmadebyforging,casting,or
bons) in the feedstock. Gas porosity on the surface can
welding. Additive manufacturing produces layers melted or
interferewithorprecludecertainNDTmethods,whileporosity
sintered on top of each other. The part’s shape is controlled by
inside the part can reduce strength in its vicinity. Like voids,
a computer as well as by the layers. The computer directs
gas porosity causes a part to be less than fully dense.
energyfromalaserorelectronbeamontoapowderbedorwire
3.4.13 porosity (keyhole), n—a type of porosity character-
input material.These processing approaches have the potential
ized by a circular depression formed due to instability of the
of creating flaws that are undesirable in the as-built or finished
vapor cavity during processing. part. In general, processing parameter anomalies and disrup-
tions during a build may induce such “flaws.” Flaws can also
3.4.13.1 Discussion—Keyhole porosity is created when the
be introduced because of contaminants present in the input
energy density is sufficiently high to cause a deep melt pool
material.
resulting in hydrodynamic instability of the surrounding liquid
4.2 Established NDT procedures such as those given in
metalandsubsequentcollapse,leavingavoidattherootofthe
keyhole. Like generic voids and gas porosity, keyhole porosity ASTM E07 standards are the basis for the NDT procedures
discussed in this guide. These NDT procedures are used to
causes a part to be less than fully dense.
3.4.14 powder bed fusion (PBF), n—an additive manufac- inspect production parts before or after post-processing or
finishingoperations,orafterreceiptoffinishedpartsbytheend
turingprocessinwhichthermalenergyselectivelyfuses(melts
or sinters) regions of a powder bed. userpriortoinstallation.TheNDTproceduresdescribedinthis
guide are based on procedures developed for conventionally
3.4.15 probability of detection (POD), n—the fraction of
manufactured cast, wrought, or welded production parts.
nominal discontinuity sizes expected to be found given their
existence.
4.3 Application of the NDT procedures discussed in this
guide is intended to reduce the likelihood of material or
3.4.16 soak time, n—the period during which a thermal
component failure, thus mitigating or eliminating the attendant
image is acquired beginning with the introduction of a gas or
risks associated with loss of function, and possibly, the loss of
liquid into the additively manufactured part.
ground support personnel, crew, or mission.
3.4.17 thermal conductivity, n—the time rate of steady heat
4.4 Input Materials—The input materials covered in this
flowthroughthethicknessofaninfiniteslabofahomogeneous
materialperpendiculartothesurface,inducedbyunittempera- guide consist of, but are not limited to, ones made from
aluminum alloys, titanium alloys, nickel-based alloys, cobalt-
ture difference.
chromiumalloys,andstainlesssteels.Inputmaterialsareeither
3.4.17.1 Discussion—Thepropertyshouldbeidentifiedwith
powders or wire.
a specific mean temperature, since it varies with temperature.
NOTE 3—When electron beams are used, the beam couples effectively
3.4.18 thermal diffusivity, n—the ratio of thermal conduc-
withanyelectricallyconductivematerial,includingaluminumandcopper-
tivity to the product of density and specific heat; a measure of
based alloys.
the rate at which heat propagates in a material; units [length
-1
4.4.1 Powders—High-qualitypowdersrequiredforAMpro-
time ].
cess are produced by (1) plasma atomization, (2) inert gas
3.4.19 thermal discontinuity, n—a change in the thermo-
atomization, or (3) centrifugal atomization using rotating
physical properties of a specimen that disrupts the diffusion of
electrodes (Fig. 1).
heat.
4.4.1.1 One of the critical features of powders is the sieve
3.4.20 voids, n—a general term encompassing both
sizeofthematerial.Metalpowderisscreenedthroughwiretest
irregularly-shaped or elongated cavities (process-induced
sieves as described in Specification E11. Section 5 andTable 1
porosity, LOF, skipped layers, large cracks, or delamination)
in Specification E11 provide nominal dimensions and critical
and spherically-shaped cavities (gas-induced and keyhole po-
dimensions of the sieves.
rosity).
4.4.1.2 Inclusions, if they exist within the raw powder, can
3.4.20.1 Discussion—InPBF,thesecavitiescanbeemptyor beequaltothesievesizediameter,andbyaruleofthumbhave
filled with partially or wholly unfused powder. Voids are a ratio of length to diameter size of 4:1.
ϵ1
E3166 − 20
FIG. 1 Three Different Powders of the Same Titanium Alloy
4.4.2 Wire—The diameter of the wire feedstock is the general, the NDT inspection requirements for these aerospace
controlling factor determining the smallest detail attainable parts will be more stringent than for AM parts intended for
using this process: fine diameter wires may be used for adding general use. For additional guidance on determining the
finedetailsandlargediameterwirestoincreasedepositionrate appropriate level of NDT relative to part category (for
during bulk deposition.Wire-fedAM equipment (for example, example, prototype parts, production parts, non-structural
EBF3 systems) can be fitted with two wire feeders that can be parts, primary structure fracture critical parts), refer to Section
controlled simultaneously and independently. For example, 5.
two wire feeders may be loaded with either a fine and a coarse
4.6 Processes—TheAM processes covered in this guide are
wire diameter for different feature definition or two different
differentiated by input material (powder or wire), energy
alloys to facilitate producing components with compositional
source (electron beam, laser beam, and plasma arc), and the
gradients.
degree of fusion (melting or sintering) (Fig. 3). Arc energy
4.5 Inspection Requirements—The aerospace parts covered sources (typically GTA (gas tungsten arc), PA (plasma arc),
by this guide can be used in either fracture critical or PTA(plasma transferred arc), and GMA(gas metal arc)) used
non-fracturecriticalapplications,forwhichtheconsequenceof in DED are not discussed in this guide. For purposes of this
part failure may or may not be severe, or the design margin guide,theAMprocessesaredefinedbyISO/ASTM52900and
may or may not be low. These parts can either be high value are subdivided into two additive manufacturing process cat-
assets manufactured in one-off or limited quantity production egories: (1) PBF and (2) DED. For a discussion of the relative
runs, such as the rocket engine baffle shown in Fig. 2, or they merits of the PBF and DED processes according to build
can be assets manufactured in higher volume production runs, volume, detail resolution, deposition rate, power efficiency,
such as turbine blades and LEAP engine fuel nozzles. In coupling efficiency, and cleanliness, consult Guide F3187. For
FIG. 2 Additively Manufactured Baffle for A Rocket Engine Built Using Selective Laser Melting and Inspected by Structured Light to De-
termine External Dimensions (Left) and Computed Tomography to Detect Internal Features (Right) (Courtesy of NASA Marshall Space
Flight Center)
ϵ1
E3166 − 20
FIG. 3 Common Additive Manufacturing Processes for Metals
details on DED feedstock, processing equipment (machine 4.6.1 Powder Bed Fusion (PBF)—In PBF systems, the
preparation, conditioning, calibration, and monitoring), atmo- energy source (electron beam or laser) is generally stationary,
spheric control, post-processing, safety, manufacturing plan,
andisfocusedatasetdepositionplaneandthebeamsteeredby
and process specification, also consult Guide F3187.
optical or magnetic means. The feedstock in PBF systems is a
powder that is fed from hoppers and screed to a uniform
NOTE 4—Other AM processes, namely, vat photopolymerization, ma-
thickness at the beginning of each melt pass. After placement
terial jetting, binder jetting, material extrusion, and sheet lamination
covered in ISO 17296-2, that rely on other energy sources such as a
of the powder, the energy source is swept rapidly across the
chemical reaction (for example, photopolymerization), or are specific to
powder bed to melt and consolidate the current layer. Follow-
additive manufacturing of polymers and ceramics, are not considered in
ing consolidation, the build platform is indexed down by one
this guide.
FIG. 4 Laser-beam Powder Bed Fusion
ϵ1
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material fully to form a solid, homogeneous 3-D part.
layer thickness, and the process is repeated, building the part
NOTE7—LasercusingisatypeofSLMprocesswhereeachlayerofthe
layer by layer (Fig. 4). Each PBF approach (Selective Laser
required cross section is divided into a number of segments called
Melting (SLM), Direct Metal Laser Sintering (DMLS), Selec-
“islands,”whichareselectedstochasticallyduringscanning.Thisstrategy
tive Laser Sintering (SLS), and EBM (Electron Beam Melt-
ensures thermal equilibrium on the surface to reduce part stresses.
ing)) has merits, and selection is based on the parts being
(2) Direct Metal Laser Sintering (DMLS)—The term
fabricated. Both PBF and DED processes use ComputerAided
‘DMLS’was originally introduced as a vendor-specific (EOS)
Design (CAD) 3-D model data, which are prepared by “slic-
product line analogous to SLM-based product lines. In both
ing” the model into build layers. Build volumes of the order of
cases, fully dense, high strength parts with minimal porosity
64L (40 × 40 × 40cm) (4000in. (~16 × 16 × 16in.)) are
were produced. ‘DMLS’ used in this context, however, is a
possible.
misnomer and arguably archaic, and is thus not preferred. In
other (preferred) usage, DMLS denotes a process, in which a
NOTE 5—Selective Laser Melting (SLM) or Direct Metal Laser Sinter-
metal alloy is not heated enough to produce complete melting.
ing (DMLS) use a high power-density laser to melt and fuse metallic
powders together. SLM is considered a subcategory of Selective Laser Thistechniqueisespeciallyusefulformetalalloysversuspure
Sintering (SLS). The SLM or DMLS process has the ability to melt the
metals, where partial melting is advantageous. DMLS is also
metalmaterialfullytoformasolid3-Dpart,unlikeSLS.SLSusesalaser
known as Direct Metal Laser Melting (DMLM).
tosinterpowderedmaterial(oftenapolymer,butceramicsandmetalscan
(3) Selective Laser Sintering (SLS)—A lower energy AM
also be used), producing different properties (crystal structure, porosity,
process, which involves partial melting of the input material.
etc.) than are produced in SLM or DMLS. SLS has mainly been used for
rapid prototyping and for low-volume production of parts. Like SLM, SLS produces parts with dimensional accuracy and
complex geometries; however, support structures are generally
4.6.1.1 Laser-Powder Bed Fusion (L-PBF)—Lasers (for
not required. SLS parts are also less the fully dense, exhibiting
example, Nd-YAG) are used to fuse powders partially (sinter-
surface and bulk porosity. SLS is mainly used for rapid
ing) or completely (melting). Sources of powder, specifically
prototypingandforlow-volumeproductionofparts.WithSLS,
optimized for PBF, are available in a range of common
it is possible to reduce shrinking and warping by heating the
engineeringalloyswhilesmalllotsizesofspecialtypowderare
buildchambertoatemperaturejustbelowthatneededtosinter
becoming increasingly available. Variations in L-PBF equip-
the powdered metal, polymer, or ceramic.
ment exist from vendor to vendor as well as in the proprietary
NOTE 8—SLS is used with a wider range of materials (metals,
procedures offered by each supplier to melt or sinter the metal
polymers, and ceramics) than DMLS (metals). The lower laser power
into a formed part. Unique aspects of the PBF process (as
produces different properties (crystal structure, porosity, etc.) than are
compared with most conventional metal fabrication processes) produced by SLM.
include the rapid melting and cooling rate, a narrow melt pool,
4.6.2 Electron Beam-Powder Bed Fusion (EB-PBF)—
planar deposition, powder morphology, and the need for
Electron beam powder bed fusion (EB-PBF) is similar to
support structures. Surface conditions typically feature a layer
L-PBF in many of the challenges presented to NDT examina-
of partially fused powder and irregularities such as stair
tion. Differences with L-PBF include a smaller selection of
stepping. The as-deposited material in the bulk displays band-
powder alloys optimized for EB-PBF, a vacuum versus inert
ing and planar variations in microstructure and may include
gas build chamber, different designs for support structures
regions of unfused or partially fused powder. Post-processing
(used for heat conduction versus structural support), rougher
proceduresincludeheattreatment,hotisostaticpressing(HIP),
surfaces,andlargermeltpools.EB-PBFistypicallyperformed
machining, and surface finishing. The biggest challenge in the
at higher temperatures using an electron beam emitted by a
application of NDT to metal parts made by PBF processes is
heated tungsten filament, producing a deeper melt pool com-
the flaw size (sub-micron to mm scale) and location (poten-
pared with L-PBF. Each powder bed layer is also scanned in
tially everywhere).
two stages, the preheating stage and the melting stage. The
(1) Selective Laser Melting (SLM)—A PBF process in
larger melt pool results in poorer dimensional control and
which a high-energy laser selectively melts regions of thin
surface quality, but allows for high build rates and reduced
layer of fine metal powder (powder bed) in the build chamber
residual stress. Preheating the powder bed layer on EB-PBF
as directed by a computer. Since the input material is fully
further reduces the thermal gradient between the powder bed
melted, an extremely dense, homogeneous, and strong part is
andthescannedlayer,whichinturnreducesresidualstressesin
produced with good surface quality and minimal porosity. The
the part and the corresponding need for post-process heat
-4
high temperature gradients that occur during the SLM process
treatment. The high vacuum (<10 mPa (<10 torr)) chamber
can also lead to stresses inside the final part, which can lead to
environment offers a high level of purity for reactive metals,
part distortion. The chamber often is filled with argon or other
thus reducing the production of flaws associated with contami-
inert shield gas to provide a non-contaminating atmosphere.
nation and pickup of oxygen, nitrogen, and other impurities.
The process starts by slicing 3-D CAD file data into layers,
Post-processingremovalofpowderfrominternalvolumesmay
usually 20 to 100microns (0.8 to 4mils) thick, creating a 2-D
be more challenging than with L-PBF. As with L-PBF, heat
image of each layer. SLM produces parts with dimensional
treatment, hot isostatic pressing, machining, and surface fin-
accuracyandcomplexgeometries;however,supportstructures
ishing may still be required to facilitate the successful appli-
are usually required during printing to reduce internal stress
cation of NDT procedures.
and distortion. Synonym: direct metal laser melting (DMLM).
4.6.2.1 Electron Beam Melting (EBM)—A free form EB-
PBF fabrication method, which uses pre-alloyed powder, a
NOTE6—SLMisconsideredasubcategoryofSelectiveLaserSintering
(SLS), but unlike SLS, the SLM process has the ability to melt the metal heated fusion bed, an electron beam, and a high vacuum build
ϵ1
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chamber. This process creates full melting with the material lenges for direct application of existing NDT methods and the
characteristics of the target material. Build chambers are small definition of allowable flaw sizes and locations.
with larger ones under development.
4.6.3.2 Electron Beam DED With Wire (DED-w)—Electron
4.6.3 Directed Energy Deposition (DED)—Incontrasttothe
beam DED is similar to electron beam welding in conduction
layer-by-layerPBFscreeningandmeltpassprocess,powderor
mode melting (verses keyhole mode), featuring similar flaw
wire feedstock for DED is delivered to the melt pool in
morphology and evaluation using similar NDT methods. The
coordination with a focused energy source and a shield gas or
process creates a large 3-D weld clad build-up to a near net
vacuum, and the deposition head (typically) indexes up from
shaped requiring post deposition machining and often heat
the build surface with each successive layer. DED systems are
treatments or hot isostatic pressing to achieve a final part.
differentiated from PBF systems by the following general
Uniqueaspectsoftheprocessincludethehighpurityshieldgas
characteristics: ability to process large build volumes (up to
or vacuum environment of the chamber, the extended time at
5000L(1.6×1.6×2.1m)(175ft (5×5×7ft))withminimal
temperature of a build cycle, and the effect of as-deposited
toolingandsecondaryprocessing,abilitytoproducepartswith
grain structure, alloy segregation, distortion, and residual
either composition gradients or hybrid structures consisting of
stress. Operation in a vacuum ensures a clean process environ-
multiple materials having different compositions and
ment and eliminates the need for a consumable shield gas.
structures, ability to process at relatively high deposition rates,
Defects are similar to those found in inert gas arc welds and
use for part repair and feature addition, and the use of
those associated with dissimilar combinations of the base
articulated energy sources and feedstock delivered directly to
featurealloy(forexample,plateorshaftsubstrates)verseswire
the melt pool.
feedstock alloy.Awide range of weld wire alloys, certified for
NOTE 9—Although DED systems can be used to apply a surface
conventional weld processing, are available.
cladding, such use does not fit the current definition of additive manufac-
turing (AM). Cladding consists of applying a uniform buildup of material 4.6.3.3 Electron Beam Freeform Fabrication (EBF )—This
on a surface. To be considered AM, a CAD file of the build features is
rapid direct metal deposition process can be used to build a
converted into section cuts representing each layer of material to be
complex,unitizedpartinalayer-additivefashion,althoughthe
deposited. The DED machine then builds up material, layer-by-layer, so
more immediate benefit is for use as a manufacturing process
materialisonlyappliedwhererequiredtoproduceapart,addafeature,or
for adding details to components fabricated from simplified
make a repair.
castings and forgings or plate products. The EBF process
4.6.3.1 Laser DED With Powder—Laser beam DED relies
introduces metal wire feedstock into a molten pool that is
on laser melting of powder feed stock, including both powders
created and sustained by a focused electron beam in a vacuum
used for L-PBF but also a wider range of alloy powders
-4 3
environment (10mPa (10 torr) or lower). EBF systems can
available for more common metal powder processing applica-
be fixed or portable (Fig. 5) and consist of a high power
tions such as laser cladding. The process may be used to form
electron beam gun and single or multiple wire feeders capable
entire parts or may be applied to an existing substrate or base
ofindependentorsimultaneousoperation.Otherfeaturesofthe
component such as with refurbishment, remanufacturing, or
EBF process include:
hybrid (additive/subtractive) processing. Surface and subsur-
(1)Programmable positioning using four (X, Y, Z, and
face conditions, flaws, and defects are similar to other PBF
melted deposits and those of conventional laser welds. Defects rotation) to six axes of motion (X,Y, Z, gun tilt, positioner tilt,
and rotate).
may occur with the dissimilar combination of the base feature
alloy, with the AM deposited alloy. The relatively small and (2)Near 100% efficient in feedstock consumption and
distributed flaw size and surface condition may create chal- approaches 95% efficiency in power usage.
FIG. 5 Ground-based (Left) and Portable (Right) Electron-Beam Freeform Fabrication Systems (Courtesy of NASA Langley Research
Center)
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determine if flaws are eliminated or introduced by post-processing, or to
(3) Rapid bulk metal deposition rates in excess of
3 3
screen raw, as built parts before performing labor intensive post-
2500cm /hr (150in. /hr) as well as finer detail at lower
processing steps.
deposition rates with the same equipment.
4.8 Flaws—The occurrence of flaws in AM parts is gov-
(4)Viablesolutionstotheissuesofdepositionrate,process
erned by the particular material, processing, post-processing,
efficiency, and material compatibility for insertion into the
and service history experienced by the part. The flaw types
production environment.
uniquetotheAMprocessescoveredinthisguidearestillbeing
4.6.3.4 Laser DED with Wire (DED-w)—This rapid direct
identified and their effects on final properties determined. The
metal deposition process can be used to build complex,
flaw type for which the NDT capability is demonstrated is
unitized parts in a layer-additive fashion, or be used to add
based on the level of understanding at the time of the part’s
details to traditionally manufactured components. The laser
design and the projected future screening importance. Metal
DED-w process introduces metal wire feedstock into a molten
parts fabricated by additive manufacturing can have cracks,
pool that is sustained using a laser energy source (Fig. 6).
porosity, LOF, trapped powder, inclusions, stop/start-type
Operationinanargontentenvironmentwithoxygenlevelslow
flaws, residual stress, and poor dimensional accuracy (Figs.
as200ppmensuresminimaloxidationandeliminatestheneed
9-11).Partscanalsohaveflawsintroducedbypost-processing,
for a vacuum pump and chamber (Fig. 7). Systems can consist
or damage caused by qualification testing before being placed
of multiple laser power sources or multiple wire feeders, or
into service. Once in service, additional damage can be
both, capable of independent or simultaneous operation. De-
incurred due to impact, cuts/scratches/abrasion, exposure to
position rates are scalable to laser power. For Ti-Al6-V4,
aerospace media, loading stresses, thermal cycling, physical
deposition rates approach 2kg⁄hr per 10kW of laser power.
aging, oxidation, and weathering. These factors will lead to
The process is nearly 100% efficient in feedstock consump-
complex damage states in the part that can be visible or
tion.
invisible, macroscopic or microscopic. These damage states
4.7 Post-Processing—Stress relief, HIP, heat treatment, and
can be characterized by the presence of de-densification,
polishing can affect the size and distribution of volumetric and
depressions, chemical modification, microstructural variation,
surface flaws, and, therefore, the efficacy of the
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