Materials Used in Selective Laser Melting (SLM)

Selective Laser Melting (SLM) refers to the additive manufacturing (AM) process that builds up a complex three-dimensional (3D) object by using a laser beam to melt powder materials [1]. SLM has been considered one of the most versatile technologies as it can process a wide variety of materials, particularly metals and alloys [2]. Its most suited applications are in the aerospace, automotive, construction, food, and jewellery industries [3].

The most common powder materials used in SLM include:

  • Steel and iron-based alloys
  • Nickel-based alloys
  • Titanium-based alloys
  • Aluminium alloys
  • Alumina
  • Silicon carbide
  • Yttria stabilised zirconia

 

Here, you will learn about:

  • What selective laser melting is
  • What materials are used for selective laser melting
  • How the market for selective laser melting is expected to grow
  • What would some future applications of selective laser melting be

SLEDM_1

(Credit: 3D natives)

What is selective laser melting?

SLM is an additive manufacturing process in which powder materials are melted using a high-power laser and solidified in successive layers to produce a complex 3D physical model [1]. This process uses metal powders as raw materials [2]. A thin layer of the metal powder is deposited on a substrate plate, and the laser heats and melts the powder particles following a computer-aided design (CAD) [2]. SLM is also known as laser powder bed fusion (LPBF) or direct metal laser melting (DMLM) [1]. Some of SLM’s advantages and limitations include the following [4][5].

Table 1. Advantages and Limitations of the Selective Laser Melting Technology

Advantages

Limitations

High accuracy

Accuracy requires longer durations in the process

Functionality

High surface roughness and high residual stress

Minimal post-processing

Anisotropic properties

Wide variety of materials (some under development)

Deficiency of quality on-line control

Allows the creation of complex and unique shapes from metal powders

High cost of equipment and materials

Surface structuring (including micro- and nano-structuring)

Requires an inert gas supply

High recyclability of the raw material

Difficulty in removing powder from small channels

What materials are used for selective laser melting?

Early applications of SLM only included cast iron, titanium, and nickel. These were used mainly due to their abundance in nature, opportunities for widespread applications, and cost. Later, SLM research progressed, and other metals were included such as aluminium, copper, cobalt, tungsten, and their alloys and composites [4]. Table 2 presents an overview of some of the most common metal powders used in SLM and their applications.

Table 2. Materials for Selective Laser Melting

Materials

Properties

Applications

Alloy Examples

Steel and Iron-based alloys

High corrosion resistance

High strength (less malleable)

Surface roughness

Relative density (>90%)

Micro-hardness

Medical and biomedical (i.e., implants)

Dental (i.e., orthodontic products)

Heat exchangers

Lightweight structures (i.e., honeycomb-like structures)

Other application (i.e., filter elements)

Fe-Ni

Fe3Al

Fe-Ni-Cr

Fe-Ni-Cu-P

304L stainless steel

316L stainless steel

H13 tool steel

H20 tool steel

Maraging steel

Ultra-high carbon steel

Titanium-based alloys

High relative density (>98%)

Superior shear strength (higher or equal compared to its counterparts)

Surface roughness

Low porosity

Medical and dental (i.e., body prosthesis, dental implants)

Lightweight structures (i.e., scaffolds)

CP-Ti

Ti-6Al-4V

Ti-6Al-7Nb

Ti-24nb-4Zr-8Sn

Ti-13Zr-Nb

Ti-13Nb-13Zr

Nickel-based alloys

High-temperature resistance

Fatigue strength

Excellent corrosion resistance

Wear resistance

Good weldability

Relative density (near 100%)

Aircraft engines

Combustion chambers

Die models for bevel gear

Porous filtration media

Inconel 625

Inconel 718

Chromel

Hastelloy X

Nimonic 263

IN738LC

MAR-M-247

Ni-Ti

Other Metals  (Aluminium, Copper, Magnesium, Cobalt-Chrome, Tungsten, Gold, Silver)

High relative density of aluminium and cobalt-chrome (>96%) and other metals (82%-85%)

High strength in aluminium (i.e., 400 MPa for AlSiMg)

Increased hardness of parts when powder copper has been added

 

Biomedical and dental applications (i.e., crowns and bridges)

Heat exchangers

Automobile parts

Jewellery

Al6061

AlSi10Mg

Cu+Cu10Sn+Cu8.4P

CoCr

24 Carat gold

Tungsten

K220

CuNi15C18400

Ceramics

High melting temperatures

Brittle nature

High surface roughness

Medical and dental (i.e., dental restorations, bone substitution implants

Thin wall structures

Electrical or thermal insulation

Wear resistance coating

Glass-ceramics

Alumina

Silica

Yttria stabilized zirconia

Tri-calcium phosphate

Alumina zirconia Mixture

Porcelain

Silicon Carbide

The market for SLM materials

The market for additive manufacturing with metal powders was at about USD 366 million in 2019. It is forecasted to grow over 18% (compound annual growth rate) between 2020 and 2026 to reach around USD 970 million by 2026. Advancements in technology would be focused on lighter and cleaner products as well as shorter processing time and cost [6].

Depositphotos_299690482_xl-2015 (1)

Future applications

The SLM technology generally uses powder particles sizes ranging between 20 to 50 mm and layer thicknesses between 20 to 100 mm. Recent efforts have scaled down the technology to work with particles sizes of less than 10 mm and layer thickness of less than 10 mm. This technology is known as micro SLM, and it is expected to continue to evolve and find applications in cell biology, biomedical science, and clinical diagnostics. [7].

The aerospace and automobile industries are envisioning installing devices and sensors at microscale and nanoscale resolution through precise macrostructure control.

Another industry that would continue to evolve is the jewellery industry with efforts to include more precious metals such as gold, platinum, and palladium alloys. These also involve achieving near-net shape fabrication, decreasing material waste, and increasing efficiency in the manufacturing process [7].

Sources

[1] Xu Song, Wei Zhai, Rui Huang, Jin Fu, Mingwang Fu, Feng Li, 2020, Metal-Based 3D Printed Micro Parts & Structures, Reference Module in Materials Science and Materials Engineering, Elsevier, 2020

[2] Prashanth Konda Gokuldoss, Sri Kolla, Jürgen Eckert, 2017, Additive Manufacturing Processes: Selective Laser Melting, Electron Beam Melting and Binder Jetting—Selection Guidelines, Materials, 2017 Jun 10(6): 672

[3] Prashanth Konda Gokuldoss, 2020, Selective Laser Melting; Materials and Applications, MDPI Books, Basel Switzerland

[4] Chord Yen Yap, Kai Se Chua, 2015, Review of selective laser melting: Materials and Applications, Applied Physics Reviews, 2(4), December 2015, Available,  https://www.researchgate.net/publication/286497734_Review_of_selective_laser_melting_Materials_and_applications (accessed January 29, 2021)

[5] Interreg, Sudoe, Addispace, Diagnosis and Study of Opportunities of Metallic Additive Manufacturing on Sudoe Aerospatial Sector, [Online] Available: http://www.addispace.eu/gestor/recursos/uploads/imagenes/noticias/INFORME/State_of_the_art_MAM-ENGLISH_low.pdf (accessed January 29, 2021)

[6] Kunal Ahuja, Sonal Singh, 2020, Additive Manufacturing with Metal Powders Market Size, Global Marketing Insights, Report ID: GM1783, June 2020, [Online] Available: https://www.gminsights.com/industry-analysis/additive-manufacturing-with-metal-powders-market(accessed January 29, 2021)

[7] Balasubramanian Nagarajan, Zhiheng Hu, Xu Song, Wei Zhai, Jun Wei, Development of Micro Selective Laser Melting, The State of the Art and Future Perspectives, Engineering, Volume 5, Issue 4, pages 702-720, August 2019.

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