ISO/ASTM TR 52905:2023

TECHNICAL ISO/ASTM TR
REPORT 52905
First edition
2023-06
Additive manufacturing of metals —
Non-destructive testing and evaluation
— Defect detection in parts
Fabrication additive de métaux — Essais et évaluation non destructifs
— Détection de défauts dans les pièces
Reference number
© ISO/ASTM International 2023
© ISO/ASTM International 2023
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Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 NDT potential for authentication and/or identification . 2
5 List of abbreviated terms . 3
6 Typical flaws/defects in AM .4
6.1 Flaw origins/causes . 4
6.2 Flaw/defects classification . 4
6.3 Defect classification strategies for AM .12
7 NDT standards review .13
7.1 Post-process NDT standards . 13
7.1.1 ISO review . 13
7.2 In-process NDT review .15
8 Standard selection structure for AM .18
9 NDT techniques potential for AM only defects .19
10 AM artefacts .28
10.1 Design .28
10.1.1 Star artefact .28
10.1.2 À la carte artefact .34
10.2 Manufacturing .36
10.2.1 Star artefact . 36
10.2.2 À la carte artefact . 37
11 NDT method trials and validation using star artefact .38
11.1 Experimental trials .38
11.1.1 X-ray Computed Tomography – XCT (MTC & GE & EWI) .39
11.1.2 Neutron Imaging — NI and Synchrotron radiation — SX (HZB & ESRF) . 43
11.1.3 Thermography Testing — TT (University of Bath) .50
11.1.4 Resonant Ultrasound Spectroscopy methods — RUS . 59
11.1.5 Ultrasonic testing — UT and Phase Array UT — PAUT (EWI and NIST and
LNE) . 75
11.1.6 Residual stress — RS (ILL) .80
12 Defect built validation star artefact (Cut-off MTC) .85
12.1 Summary of procedure by XCT .85
12.1.1 Apparatus .86
12.1.2 Significance of data/interpretation of results .87
12.2 Summary of procedure by metallography .90
12.2.1 Apparatus . 91
12.2.2 Significance of data/Interpretation of results . 91
12.3 Comments/observations .93
13 NDT trials for à la carte artefact .94
13.1 Summary of procedure .94
13.2 Apparatus .94
13.3 Significance of data/interpretation of results.94
13.4 Comments/observations .97
14 Summary of the trials findings by material .97
15 Main conclusions. 101
iii
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Annex A (informative) Causes and effects of defects in wire DED and PBF process . 104
Annex B (informative) Review of existing NDT standards for welding or casting for
application of post build AM flaws . 106
Annex C (informative) Star artefacts using during the trials . 111
Annex D (informative) Summary of star artefact manufacturing and NDT technologies for
trials . 115
Annex E (informative) XCT parameters and XCT set up used for inspection and validation . 118
Annex F (informative) Parameters and set up for Neutron Image (NI) and Synchrotron (Sx)
inspection . 135
Annex G (informative) Set up for PT and SHT inspection .141
Annex H (informative) Ultrasonic test . 144
Annex I (informative) Residual stress characterisation of Ti6Al4V by Neutron diffraction . 155
Bibliography . 157
iv
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Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
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www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 261, Additive manufacturing, in cooperation with
ASTM Committee F42, Additive manufacturing technologies, on the basis of a partnership agreement
between ISO and ASTM International with the aim to create a common set of ISO/ASTM standards
on additive manufacturing, in collaboration with the European Committee for Standardization (CEN)
Technical Committee CEN/TC 438, Additive manufacturing, in accordance with the Agreement on
technical cooperation between ISO and CEN (Vienna Agreement).
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
v
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Introduction
In response to the urgent need for standards for Additive Manufacturing (AM), this document initially
indicates Non-Destructive Testing (NDT) methods with potential to detect defects and determine
residual strain distribution that are generated in AM processes. A number of these methods were
verified. The strategy adopted was to review existing NDT standards for matured manufacturing
processes which are similar to AM, namely casting and welding. This potentially reduces the number of
standards required to comprehensively cover the defects in AM. For identified AM unique defects, this
document proposes a two-level NDT approach: a star artefact as an Initial Quality Indicator (IQI) and
à la carte artefact where an example shows the specific steps to follow for the very specific unique AM
part to be built, paving the way for a structured and comprehensive framework.
Most metal inspection methods in NDT use ultrasound or X-rays, but these techniques cannot always
cope with the complicated shapes typically produced by AM. In most circumstances X-ray computed
tomography (CT) is a more suitable method, but it also has limitations and room for improvement or
adaptation to AM, on top of being a costly method both in time and money.
This document includes post-process non-destructive testing of additive manufacturing (AM) of
metallic parts with a comprehensive approach. It covers several sectors and a similar framework can
be applied to other materials (e.g. ceramics, polymers, etc.). In-process NDT and metrology standards
are referenced as they are being developed. This document presents current standards capability to
detect which of the Additive Manufacturing (AM) flaw types and which flaws require new standards,
using a standard selection tool. NDT methods with the highest potential will be tested.
vi
© ISO/ASTM International 2023 – All rights reserved

TECHNICAL REPORT ISO/ASTM TR 52905:2023(E)
Additive manufacturing of metals — Non-destructive
testing and evaluation — Defect detection in parts
1 Scope
This document categorises additive manufacturing (AM) defects in DED and PBF laser and electron
beam category of processes, provides a review of relevant current NDT standards, details NDT methods
that are specific to AM and complex 3D geometries and outlines existing non-destructive testing
techniques that are applicable to some AM types of defects.
This document is aimed at users and producers of AM processes and it applies, in particular, to the
following:
— safety critical AM applications;
— assured confidence in AM;
— reverse engineered products manufactured by AM;
— test bodies wishing to compare requested and actual geometries.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 11484, Steel products — Employer's qualification system for non-destructive testing (NDT) personnel
ISO/ASTM 52900, Additive manufacturing — General principles — Fundamentals and vocabulary
ASTM E1316, Terminology for Nondestructive Testing
EN 1330-2, Non-destructive testing — Terminology — Part 2: Terms common to the non-destructive
testing methods
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/ASTM 52900, ASTM E1316,
EN 1330-2, ISO 11484, and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
flaw type
identifiable features that defines a specific flaw
Note 1 to entry: defect term, this word is used when a flaw that does not meet specified acceptance criteria and
is rejectable.
Note 2 to entry: Flaw term, an imperfection or discontinuity that is not necessarily rejectable
© ISO/ASTM International 2023 – All rights reserved

3.2
lack of fusion
LOF
type of process-induced porosity, in which the powder or wire feedstock is not fully melted or fused
onto the previously deposited substrate
Note 1 to entry: In PBF, this type of flaw can be an empty cavity, or contain unmelted or partially fused powder,
referred to as unconsolidated powder.
Note 2 to entry: LOF typically occurs in the bulk, making its detection difficult.
Note 3 to entry: Like voids, LOF can occur on the build layer plane (layer/horizontal LOF) or across multiple build
layers (cross layer/vertical LOF).
3.3
unconsolidated powder
unmelted powder that due to process failure was not melted and became trapped internally
3.4
layer shift
when it is disturbed by a magnetic field a layer or a number of layers are shifted away from
the other build layers
Note 1 to entry: see stop/start for PBF laser/E beam.
3.5
trapped powder
unmelted powder that is not intended for the part but is trapped within internal part cavities
3.6
porosity
presence of small voids in a part making it less than fully dense
Note 1 to entry: Porosity may be quantified as a ratio, expressed as a percentage of the volume of voids to the
total volume of the part.
[SOURCE: ISO/ASTM 52900:2019, 3.11.8]
4 NDT potential for authentication and/or identification
Some of the NDT methods in this technical report have the additional potential to extract authentication
and/or identification apparatus or design embedded in the design of the AM part. Such a potential
clearly depends on the material(s), geometry and process selected to fabricate the part, however
the design information and AM data file can embed in its geometry or texture ad-hoc devices that
potentially could be extracted by NDT techniques. ISO/TC 292 specifies and maintains a number of
standards supporting such devices within the ISO referential, and are fully applicable to AM digital
information. The specific requirements of design techniques, materials, processes, NDT modalities and
applications, however, still require careful evaluation, selection and classification.
© ISO/ASTM International 2023 – All rights reserved

5 List of abbreviated terms
AM additive manufacturing
BAE British Aerospace and Engineering Systems
EB-PBF electron beam powder bed fusion
ESFR European Synchrotron Research Facility
EWI Edison Welding Institute
FMC full matrix capture
GE-PD general electric powder division
HZB Helmholtz Zentrum Berlin
ILL Institute Laue-Langevin
IR infrared
IRT infrared thermography
J & J Johnson & Johnson
LNE laboratoire national de métrologie et d'essais
PBF-LB laser powder bed fusion
DED-LB laser directed energy deposition
MTC The Manufacturing Technology Centre
ND neutron diffraction
NDE non-destructive evaluation
NDT non-destructive testing
NI neutron Imaging
NIST National Institute of Standards and Technology
NLA non-linear acoustic testing
NLR non-linear resonance testing
PAUT phase array ultrasound testing
PCRT process compensated resonance testing
PT pulse thermography
RAM resonance acoustic method
ROI Region of interest
SX X-ray synchrotron
SHT step heating thermography
© ISO/ASTM International 2023 – All rights reserved

TFM total focusing method
TMS the modal shop
UoB university of bath
XCT X-ray computed tomography
6 Typical flaws/defects in AM
6.1 Flaw origins/causes
The causes of defects across different types of AM processes can be quite different, but the defects that
they generate can be remarkably similar. Detecting the defects also does not depend on the cause, and
in general only the size and geometry (and potentially morphology) of the defect matters for detection.
[21]
The causes and effects of a number of AM flaws have been reported in the European project AMAZE .
Table A.1 and Table A.2 give explanations of the mechanisms by which these flaws are generated
and those mechanisms are linked to the process parameters selected and the resulting processing
conditions, see ISO 11484. Understanding the conditions under which flaws are generated and
simplifying the terminology used to describe these flaws will aid the drive for quality improvement
required for widespread implementation of the technology.
The flowchart displayed in Figure 1 gives an idea of the complexity of flaw generation within the
PBF process. As can be seen, the generation of one flaw type can result in an anomalous processing
condition, which in turn generates a second flaw. For example, the presence of a thick layer or low laser
(or electron beam) power can lead to under-melting, which in turn can lead to unconsolidated powder.
Coupled with the tendency of the power source to decrease the surface energy of unconsolidated
powder under the action of surface tension, ensuing ball formation may arise due to shrinkage and
worsened wetting, leading to pitting, an uneven build surface, or an increase in surface roughness; see
EN 1330-2.
Therefore, even when there are multiple causes, a single flaw type or conditions can be generated
(excessive surface roughness) causing failure by a single failure mode (surface cracking leading to
reduced fatigue properties). Alternatively, it is also conceivable that a single flaw type or condition can
cause failure by several different failure modes.
6.2 Flaw/defects classification
Post-built AM flaws have been identified based on a report from the FP7 European AMAZE project.
Potential flaws in directed energy deposition (DED) and powder bed fusion (PBF) are listed in Table 1
and Table 2 respectively. A brief description for each flaw type is also given in the tables.
Due to the similarity in manufacturing, defects from welding and casting bear some resemblance to
defects from AM processes such as PBF and DED. Defects in post-built PBF and DED parts are identified
and listed in EN 1330-2, ASTM E1316 and References [22]. As noted in Table 1 and Table 2, both
technologies have common defects such as porosity, inclusions, undercuts, geometry, LOF, and a rough
surface texture. However, the mechanisms for PBF and DED defect generation are very different, and
more importantly, the relative abundance of each defect type will be very different due to the melting
and solidification mechanisms involved (and the significantly higher thermal gradients present in DED).
DED involves imparting a momentum into the melt pool rather than melting the powder that is already
present. The important difference between the two methods is that of timescales.
© ISO/ASTM International 2023 – All rights reserved

Key
machine: inputs/choices
AM part: resulting defect/flaw
process: resulting condition
common type of failure
Figure 1 — Causes, mode of failures and defect formation in PBF AM (see ISO/ASTM 52900)
In PBF, there is a balance of timescales between melting and re-solidification. If the melt rate is too
low, then the melt pool can become unstable and break into multiple pools. If the melt rate is too high,
powder partially melts in front of the melt pool, which can cause defects or heat affected zones. In DED,
this balance is not relevant, but the powder (or wire) that is fed into the melt pool can melt sufficiently
quickly. The issue of adding cold material (with a given momentum) to a melt pool is not well understood,
but has a large effect on the Marangoni convection direction and thermal gradients present. It is likely
that the melt pool depth will be much shallower (which may reduce powder surrounding the melt pool)
and that the thermal gradients less severe (which cause a flatter melt pool), though this depends on the
wetting between substrate (which has no surrounding powder) and the melt pool. This difference in
the melt pool dynamics impacts its shape.
This has two important consequences, grain growth and bubble dynamics. Internal defects are
attributable to cracking, pores, or lack of material. Cracking has many causes, but is generally related
to the grain boundary (apart from solidification cracking). Note that the issue of “spattering” that is
© ISO/ASTM International 2023 – All rights reserved

believed to be prominent in DED (or indeed welding) is still a significant issue in PBF. For L-PBF the
issue is that of ablation at the surface of the melt pool caused by the large thermal gradients. For EB-
PBF the problem occurs from two mechanisms; ablation and charging of the powder.
Table 1 — Typical flaws in directed energy deposition
Flaw type Description
Poor surface The surface roughness on the part does not meet the target specification for the part.
finish Measurement of the surface roughness is considered out-of-scope for NDT however, visual
examination can be included.
Porosity Typically spherical in shape and contains gas. Porosities can grow in a line to form a chain
or elongated porosity.
Incomplete fusion Fusion between the entire base metal surfaces and between adjoining welds are not com-
plete. This occurs when new material has been used and the build parameters have not
been optimised. Typically, this flaw is eliminated as the process improved when all parame-
ters have been optimised.
Undercuts at the A groove melted into the base metal adjacent to the weld toe or weld face and left unfilled
toe of the welds by weld metal.
between adjoining
weld beads
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TTabablele 1 1 ((ccoonnttiinnueuedd))
Flaw type Description
Non-uniform weld These indicate errors in the process which can risk integrity of the build. Internal flaws
bead and fusion caused by this can be void, porosity, or incomplete fusion.
characteristic
Hole or void Typically occurs internally in the built part as shown in the micrograph below. It is difficult
to detect by physical examination of the part.
Non-metallic Inclusions can come from the powder or the wire feedstock. Some inclusions are intention-
inclusions ally added to the powder to improve the process (e.g. for oxidation) but they could also be
caused by contaminants in the process.
Cracking Cracking can develop from internal holes or voids which then grows to the external surface.
Lack of geometri- Variation of the part dimension from the CAD model will not be currently part of the re-
cal accuracy/steps view. Nevertheless, steps and gross variation which can be detected by visual examination
in the part are included.
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Table 2 — Typical flaws in powder bed fusion
Flaw type Description
Unconsolidat- Unconsolidated powder leading to porosity or voids. The morphology is different to gas generated pores, but the geometry
ed powder and size are not dissimilar. The image below is an example taken from RASCAL project.
Trapped pow- Unmelted powder that is not intended for the part is trapped within part cavities.
der
Layer defect Void or porosity with or without unconsolidated powder that grows on the build layer plane in a connected or semi-connected
(Horizontal manner. The image below is a vertical slice of an X-ray computed tomography scan.
lack of fusion)
© ISO/ASTM International 2023 – All rights reserved

TTabablele 2 2 ((ccoonnttiinnueuedd))
Flaw type Description
Cross layer Void or porosity with or without unconsolidated powder that grows along the build axis in a connected or semi-connected
(Vertical lack manner. The images below show vertical and horizontal slices from an X-ray computed tomography scan.
of fusion)
Vertical slice view.
Top slice view.
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TTabablele 2 2 ((ccoonnttiinnueuedd))
Flaw type Description
Porosity Typically spherical in shape and contains gas. Porosities can grow in a line to form a chain or elongated porosity. The image
below is a horizontal slice of an X-ray computed tomography scan.
Poor surface The surface roughness on the part does not meet the specification. For example, the surface roughness is higher than ac-
[24]
finish ceptable limit .
© ISO/ASTM International 2023 – All rights reserved

TTabablele 2 2 ((ccoonnttiinnueuedd))
Flaw type Description
P = 50 W, V = 200 m/s
P = 195 W, v= 1 200 m/s
Layer shift/ Variation of the part dimension from the CAD model will not be currently part of the review. Nevertheless, steps and gross
lack of variation which can be detected by visual examination are included.
geometrical
accuracy/
steps in the
part
Reduced A certain region of the part has different mechanical properties to the rest of the part.
mechanical
properties
Inclusions Inclusions can come from the contaminants in the powder. The image below is an XCT image of an inclusion taken from
project AMAZE 2.
Void Flaws created during the build process that are empty pockets or filled with partially or wholly un-sintered powder, or
partially or wholly un-fused wire. These pockets can exist in a variety of shapes and sizes. The image below is a horizontal
slice of an X-ray computed tomography scan.
© ISO/ASTM International 2023 – All rights reserved

TTabablele 2 2 ((ccoonnttiinnueuedd))
Flaw type Description
6.3 Defect classification strategies for AM
As pointed out in ISO 11484 and Reference [25], there are longstanding NDE standard defect classes
for conventionally manufactured cast, wrought, forged, and welded production parts. The defects
produced by these conventional processes will generally not be similar to those produced by AM
processes. In addition, the NDE signal attenuation characteristics in AM parts may differ from those
in conventional parts. Therefore, legacy physical reference standards and NDE procedures can be used
[25]
with caution when inspecting AM parts . This implies that until an accepted AM defect classification
and associated NDE detection limits for technologically relevant AM defects are established, the NDE
methods and acceptance criteria used for AM parts will remain part specific to design point. Variation
of AM process parameters and disruptions during build may induce a variety of defects (anomalies) in
AM parts that can be detected, sized, and located by NDE, see ISO/ASTM 52900.
In addition to defect classification strategies based on NDE detection limits for technologically relevant
defects, or acceptance criteria for the minimum allowable defect sizes, a classification strategy based on
the physical attributes possessed by defects is also possible and, perhaps, is more intuitive. For example,
defect morphology, orientation, size, and location have been found to be useful attributes for classifying
defects. Together, physical defect attributes such as morphology, orientation, size, and location provide
a powerful framework for classifying defects and can be used to complement defect classification
strategies delimited by NDE capability (minimum detectable flaw size) or acceptance criteria (critical
initial flaw size). Ultimately, the goal is to determine which of the physical defect attribute(s) play a
prominent role in influencing properties and performance.
Further refinement of NDE is possible by looking at still other physical defect attributes related to
morphology, orientation, size and location. For example, in Reference [30], tensile tests on 17-4 PH
stainless steel AM dogbones were carried out to show effect of defects on its mechanical properties.
The results revealed that the number of defects exhibited the strongest correlation to yield strength
compared to the other attributes. In addition to the defect attributes of morphology, orientation, size,
and location discussed above, the selection of an appropriate NDE method is governed by a range of
[21][22]
practical and material considerations . Practical considerations include
a) special equipment and/or facilities requirements,
© ISO/ASTM International 2023 – All rights reserved

b) cost of examination,
c) personnel and facilities qualification,
d) geometrical complexity of the part,
e) part size and accessibility of the inspection surface or volume relative to NDE used (for example the
ability to detect embedded flaws), and
f) process history and post-processing (see ASTM E3166).
While application of conventional NDE techniques is possible for AM parts with simple geometries,
topology optimized AM parts with more complex geometries require specialized NDE techniques. The
ability of each technique to detect different types of defects, as well as to locate them in the interior or
exterior surface of a part is listed. Finally, the NDE techniques are further characterized by the ability
to globally screen or detect and locate a defect.
7 NDT standards review
7.1 Post-process NDT standards
In DED, material is fused together by melting as it is being deposited. DED processes are primarily used
to add features to an existing structure or to repair damaged or worn parts. DED has many variants of
processes. The material deposited can be either powder or wire based. The heat source can be a laser,
electron beam, electric arc among others. DED processes have similarities to welding processes, and
consequently the flaws generated in DED are expected to be similar to the flaws generated in welding.
For this reason, the NDT standards for welding have been used in the review.
In PBF, powder is deposited onto a build platform bed and selectively fused using a localized energy
source (typically electron or laser beam) to form a section through the component. The build platform
is then lowered and the process is repeated until the part is produced. Unlike DED, PBF processes do
not have similarities to welding. However, there are flaws generated in PBF such as voids and porosity
that have some similarities to welding flaws. Therefore, the review of NDT standards for welding is
still relevant to PBF. In addition to welding, some common casting flaws, gas porosity, cracking and
inclusion, are similar to DED and PBF flaws. For this reason, NDT standards for castings have also been
reviewed and their applicability to AM flaws is assessed.
7.1.1 ISO review
7.1.1.1 Welding standards
The NDT standards for welding comprise of a number of standards that cover different aspects of
inspection in welding. This is described by the tree diagrams in ISO 17635:2016, Figure B.1. The welding
quality standards are specified in ISO 5817 and ISO 10042. These standards feed into ISO 17635 which
is an interface between the quality levels and the acceptance levels for indications. This standard also
describes the NDT method selection process, which splits into six method-specific standards. These
are radiographic, eddy current, magnetic particle, penetrant, ultrasonic and visual examination. At this
stage, an NDT method has been decided, and a corresponding standard describes the test procedure
and the characterisation acceptance levels. Each method has its own limitations and it is possible that,
for a given component or a target flaw, a combination of different methods is required.
The method standards are only available for conventional NDT. For radiography and ultrasonic, there
are more sub-method standards as shown in ISO 17635:2016, Figures B.2 and B.3. NDT standards for
more advanced NDT methods are not available; for example, ultrasonic phased array, X-ray computed
tomography, and thermography. It is possible that these methods are not widely accepted and used by
NDT operators within the welding industry. However for AM, there are opportunities for new standards
to be developed for the advanced methods.
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7.1.1.2 Casting standards
The NDT standards for casting have a simpler structure to those for welding. ISO 4990 categorises
casting flaws into surface discontinuities and internal discontinuities. There are standards for five
main conventional NDT methods. Each method is either for surface or internal discontinuities. The five
NDT methods are:
1) Visual examination ISO 11971 (surface)
2) Magnetic Particle Inspection ISO 4986 (surface)
3) Liquid Particle Inspection ISO 4987 (surface)
4) Ultrasonic examination ISO 4992 (internal) — Part 1 (general purposes) and Part 2 (highly stressed
components)
5) Radiographic testing ISO 4993 (internal)
Similar to welding, there is no standard available for advanced NDT methods for castings such as X-ray
computed tomography, phased array ultrasonic and thermography. These methods are not regarded as
standard methods in castings, although they could have been used following company specific internal
standards or procedures. Castings typically have simpler geometry compared to AM and welding.
Some NDT methods might not be suitable e.g. ultrasonic. Additionally, surface roughness for castings is
typically better than as-built AM components.
7.1.1.3 Welding and casting standards applicable to AM flaws
The summary of the review of current standards for welding and casting (see Table B.1) is shown
in Table 3. Flaws that would be covered by other types of inspection e.g. dimensional measurement
or material characterisation are categorised as ‘non-NDT’. All flaws listed in the table for DED are
generally covered by current NDT standards, except for the non-NDT ones. For PBF, seven flaws are
not covered by current NDT standards. Three of these are non-NDT, and four are flaws unique to AM
(unconsolidated powder, layer, cross layer, and trapped powder). The unique flaws require new NDT
recommendations which will be addressed in this document. It will also refer to newly developed
standards in other sectors such as aerospace.
As shown in Table 3, the following are the identified flaws unique to AM (PBF only) which require new
standards:
— Layer;
— Cross layer;
— Trapped powder;
— Unconsolidated powder;
© ISO/ASTM International 2023 – All rights reserved

Table 3 — Classification of directed energy deposition and powder bed fusion flaws
(Flaws unique to additive manufacturing are in bold)

Flaw type
Poor surface finish
Porosity
Incomplete fusion
Lack of geometrical accuracy/steps in part
Undercuts
Non-uniform weld bead and fusion charac-

teristic
Hole or void
Non-metallic inclusions
Cracking
Unconsolidated powder
Lack of geometrical accuracy/steps in part
Reduced mechanical properties
Inclusions
Void
Layer
Cross layer
Porosity
Poor surface finish
Trapped powder
7.2 In-process NDT review
Conventional NDE methods such as X-ray, UT, EC, have been used for post build inspection of Additive
manufacturing (AM) components. Due to the limited number of studies available and the technical
[21][27]
constraints, the capability of these NDE techniques is limited, indicating a technical gap . It is
foreseen that in-process monitoring can be used to improve control of the process to minimise quality
issues. In addition, in-process inspection has the added ability to inspect the part as it is built, which for
some very complex AM parts may be the only NDE capable solution.
AM processes offer freedom over other manufacturing methods, such as the integration of multiple
parts, which generally increase their geometry complexity. In order for an AM process to be successful,
the product quality can first be ensured. Typically, quality inspections are performed after the build of
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PBF DED
Non-NDT
Common in
DED & PBF
Covered by
current stand-
ards
Unique to AM
the full part, which becomes difficult for complex geometries. Taking advantage of the unique layer-by-
layer build method, an ideal place to verify the part quality is after a layer or number of layers, with the
potential advantage to reduce or eliminate the need to inspect after the full build.
Current AM in-process monitoring relies mainly on surface measurements, potentially missing
subsurface defects. LPBF and DED AM processes work at elevated temperatures; therefore, non-contact
methods are required.
In powder bed fusion processes, problems with layer-wise coatings and untimely laser melting can
lead to porosity, stress and further variations in the built part, or of material properties. Therefore, it
is important to not only perform measurements to inspect the finished build, but also to monitor in-
process and ultimately implement an efficient feedback system tha
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