Section 01: Introduction
The rapid evolution of manufacturing technologies has ushered in advanced
techniques like laser metal deposition (LMD), which offers significant advantages for
processing materials such as stainless steel 316L (SS316L) in demanding industrial
applications. This section introduces the transformative journey of manufacturing,
highlighting the shift from traditional subtractive methods to additive manufacturing
(AM) and the specific relevance of LMD for SS316L. It explores the historical
progression of manufacturing technologies, the rise of AM in modern industries, the
motivation for focusing on LMD-processed SS316L, and the objectives and structure
of this review. By examining these aspects, this section establishes the context for a
comprehensive analysis of process optimization, microstructure, and mechanical
properties, addressing current research gaps and industrial needs.
1.1Evolution of manufacturing technologies
The evolution of manufacturing technologies has significantly transformed industrial
production, transitioning from labor-intensive manual processes to sophisticated,
automated systems. Before the Industrial Revolution, manufacturing relied heavily on
handmade techniques using basic tools, limiting production scale and efficiency [1].
The Industrial Revolution introduced mechanization, enabling mass production
through assembly lines and significantly reducing costs while increasing output [1].
This shift marked the beginning of a paradigm change from traditional subtractive
manufacturing, which involves material removal, to modern approaches that include
additive manufacturing (AM) techniques [1, 2]. Subtractive methods, such as
machining and stamping, have been staples in conventional manufacturing, producing
reliable products but often generating significant material waste [2]. In contrast,
additive manufacturing, including processes like laser metal deposition (LMD), builds
components layer by layer from digital models, offering reduced waste and enhanced
design flexibility [2]. Key milestones, such as the development of injection molding
in the 1920s for high-volume production of complex parts, highlight the progression
of manufacturing capabilities [2]. The rise of AM has been driven by technological
advancements in computer-aided design (CAD) and material science, enabling rapid
prototyping and production of intricate geometries across industries like aerospace
and medical [1, 2]. Economic drivers, such as cost-effectiveness for low-volume
production and sustainability concerns, further propel the adoption of AM over
traditional methods, reshaping industrial structures globally [1, 2].
1.2Rise of additive manufacturing in modern industry
Additive manufacturing (AM), commonly referred to as 3D printing, has emerged as a
transformative technology in modern industry, revolutionizing the production of
complex geometries with significantly reduced material waste and shorter lead times
compared to traditional subtractive manufacturing methods. By building components
layer by layer directly from digital models, AM offers unparalleled design flexibility,
enabling the creation of intricate structures that are often unattainable through
conventional processes, making it a cornerstone technology for applications in
aerospace, automotive, biomedical, and marine industries (Singh et al., 2017). As an
integral part of Industry 4.0, AM supports the production of lightweight, high-strength
components using advanced materials like stainless steel 316L (SS316L), which is
prized for its corrosion resistance, biocompatibility, and mechanical robustness,
facilitating rapid prototyping, on-demand manufacturing, and localized production to
meet specific industry needs (Yeh and Chen, xxxx; Review Paper Outline, Section
2.2). Among AM techniques, Laser Metal Deposition (LMD), a subset of Directed
Energy Deposition (DED), stands out for its precision in depositing metal powders,
allowing for the fabrication of near-net-shape parts and the repair of high-value
components with tailored properties that enhance performance in critical applications
(Schniederjans, 2017). The ability of AM to produce small batches efficiently reduces
dependence on complex global supply chains, promoting cost-effective and agile
manufacturing processes, particularly when integrated with hybrid manufacturing
systems that combine AM with traditional methods like milling or forging (Armstrong
et al., 2022). Furthermore, AM contributes to sustainable manufacturing by
minimizing energy consumption and material waste, aligning with global demands for
environmentally responsible production practices and reducing the carbon footprint of
industrial operations (Singh et al., 2017; Review Paper Outline, Section 1.3).
However, challenges such as microstructural heterogeneity, porosity, and residual
stresses arising from the rapid thermal cycles and steep thermal gradients in LMD
processes necessitate ongoing research to optimize process parameters and ensure
consistent part quality, particularly for SS316L in high-stakes applications (Singh et
al., 2017; Yeh and Chen, xxxx). The unique thermal dynamics of LMD result in
microstructural and mechanical properties that differ from conventionally
manufactured SS316L, underscoring the need to study the interplay between
processing conditions, defect prevention, and final part performance to enhance
reliability and scalability (Armstrong et al., 2022). Additionally, the high energy
consumption associated with laser-based AM processes and the need for improved
process efficiency highlight the importance of addressing these gaps to support
broader industrial adoption (Schniederjans, 2017). As industries increasingly
prioritize customization, operational efficiency, and sustainability, the strategic
advantages of AM—particularly in enabling advanced designs, high-performance
materials like SS316L, and flexible manufacturing solutions—position it as a critical
driver of innovation and competitiveness in modern industrial ecosystems
(Schniederjans, 2017; Armstrong et al., 2022; Yeh and Chen, xxxx; Review Paper
Outline, Sections 1.3 and 2.2).
1.3Motivation behind studying LMD processed SS316L
The motivation for studying laser metal deposition (LMD)-processed SS316L,
including laser-directed energy deposition (L-DED) and wire arc-directed energy
deposition (W-DED), stems from its transformative potential in advanced
manufacturing and its critical relevance to high-performance industries. LMD’s
ability to repair high-value components and fabricate complex geometries on non-
flat surfaces addresses key demands in aerospace, biomedical, and marine
applications, where precision and durability are paramount. SS316L’s superior
corrosion resistance, biocompatibility, and mechanical strength make it an ideal
candidate for harsh environments, yet LMD processing introduces challenges,
such as larger cellular structures (3–15 μm) compared to selective laser melting
(SLM) (0.5–1 μm), which can compromise corrosion resistance and passivity
(Revilla et al., 2020). Furthermore, L-DED yields refined columnar dendritic
microstructures with higher austenite content due to rapid cooling, while W-DED
produces larger columnar structures with increased ferrite (δ) phase and high-
angle grain boundaries (HAGB, 34% vs. L-DED’s 37%), enhancing hardness and
strength (Das et al., 2023). Despite identical energy density, W-DED’s slower
cooling fosters distinct microstructural evolution, including ferrite side plates,
while L-DED’s rapid cooling promotes coherent FCC-FCC boundaries and
carbide precipitation. These differences underscore the need to optimize process
parameters to mitigate defects like porosity and inconsistent grain structures,
which can undermine component reliability. By addressing these challenges,
research into LMD-processed SS316L aims to unlock its full potential, enabling
the production of robust, high-quality components that meet stringent industry
standards and drive innovation in additive manufacturing.
1.4 Objective and scope of the review
This review aims to comprehensively evaluate the process optimization,
microstructural evolution, and mechanical properties of stainless steel 316L (SS316L)
fabricated via laser metal deposition (LMD), addressing key questions on how process
parameters influence material performance and reliability. The primary objectives are
to synthesize findings from numerous research papers studied, identify optimal
processing conditions, and highlight gaps in understanding fatigue behavior, post-
processing effects, and in-situ monitoring. The scope includes a systematic analysis of
peer-reviewed literature from databases like Scopus and Web of Science, focusing on
laser parameters, feedstock delivery, defect prevention, and their effects on
microstructure and properties such as hardness, tensile strength, and corrosion
resistance. By exploring SS316L’s critical role in high-performance applications like
aerospace and biomedical, this review seeks to provide actionable insights for
enhancing LMD process reliability and advancing industrial adoption, while noting
limitations in scalability and standardization that require further exploration.
