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Review
. 2025 Sep 14;18(18):4304.
doi: 10.3390/ma18184304.

Advancements in In-Situ Monitoring Technologies for Detecting Process-Induced Defects in the Directed Energy Deposition Process: A Comprehensive Review

Md Jonaet Ansari  1   2 , Anthony Roccisano  1   2 , Elias J G Arcondoulis  3 , Christiane Schulz  1   4 , Thomas Schläfer  4 , Colin Hall  1   2
Affiliations
Review

Advancements in In-Situ Monitoring Technologies for Detecting Process-Induced Defects in the Directed Energy Deposition Process: A Comprehensive Review

Md Jonaet Ansari et al. Materials (Basel). .

Abstract

Laser-based directed energy deposition for metallic materials (DED-LB/M) is a versatile additive manufacturing (AM) technique that facilitates the deposition of advanced protective coatings, the refurbishment of degraded components, and the fabrication of intricate metallic structures. Despite the technological advancements and potential, the presence of process-induced defects poses significant challenges to the repeatability and stability of the DED-LB/M process, limiting its widespread application, particularly in industries requiring high-quality products. In-situ process monitoring stands out as a key technological intervention, offering the possibility of real-time defect detection to mitigate these challenges. Focusing on the DED-LB/M process, this review provides a comparative analysis of various in-situ monitoring techniques and their effectiveness in identifying process-induced defects. The review categorises different sensing methods based on their sensor data format, utilised data processing techniques, and their ability to detect both surface and internal defects within the fabricated structures. Furthermore, it compares the capabilities of these techniques and offers a critical analysis of their limitations in defect detection. This review concludes by discussing the major challenges that remain in implementing in-situ defect detection in industrial practice and outlines key future directions necessary to overcome them.

Keywords: defects; directed energy deposition; in-situ monitoring technique.

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Conflict of interest statement

Authors Christiane Schulz and Thomas Schläfer were employed by the company ‘LaserBond Ltd’. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 5
Figure 5
Major porosity types observed in DED-LB/M fabricated structures. (a) Lack of fusion (LoF) [103], (b) keyhole porosity [103], and (c) gas-induced porosity [104].
Figure 1
Figure 1
Schematic representation of the DED-LB/M process, illustrating the use of metallic powder as a feedstock material, adapted from [36].
Figure 2
Figure 2
Schematic representation of powder feeding methodologies in the DED-LB/M process, adapted from [17]. (a) Co-axial powder injection, where the powder is fed symmetrically around the laser beam. (b) Off-axis powder injection, where the powder is delivered from a single direction relative to the laser beam.
Figure 3
Figure 3
Different process parameters and variables in DED-LB/M process.
Figure 4
Figure 4
Major crack types observed in DED-LB/M fabricated structures made from nickel-based superalloys. The three primary crack types are: (a) Solidification cracking [89], (b) Liquation cracking [89], and (c) Cold cracking [90]. This figure is reprinted with permission of Elsevier [90].
Figure 6
Figure 6
Inclusions observed in a DED-LB/M processed austenitic stainless-steel structure [105].
See this image and copyright information in PMC

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