# Additive manufacturing technology for thermoelectric developments

Guillaume Savelli, Guilhem Roux, Maxime Baudry

► To cite this version:

Guillaume Savelli, Guilhem Roux, Maxime Baudry. Additive manufacturing technology for thermoelectric developments. Journées Nationales de la Thermoélectricité JNTE2023, Nov 2023, Orsay, France. hal-05444584

HAL Id: hal-05444584

https://hal.science/hal-05444584v1

Submitted on 6 Jan 2026

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
<figure><img src="image_2.png" /></figure>

# Additive manufacturing technology for thermoelectric developments

Guillaume SAVELLI, Guilhem ROUX, Maxime BAUDRY

Journées Nationales de Thermoélectricité 2023 – Paris Saclay, France
# Content

* What is additive manufacturing ?

* Additive manufacturing for thermoelectrics

* Additive manufacturing for thermoelectrics at CEA
<figure><img src="image_3.png" /></figure>

# Content

* What is additive manufacturing ?

* Additive manufacturing for thermoelectrics

* Additive manufacturing for thermoelectrics at CEA

<figure><img src="image_4.png" /></figure>
# Additive manufacturing

* **Definition:**

* Additive manufacturing (AM), also known as 3D printing, usually builds 3D objects by adding materials layer upon layer to form the desired shape¹

* Coupled with computer-aided design (CAD), AM has been popularized in the rapid prototyping and customized design solutions

* **Applications²:**

* Aerospace industry & suppliers

* Automotive industry & suppliers

* Machinery (e.g. turbines, special machinery)

* Medical implants (dental, orthopedic)

* Handling and robotics

* Lifestyle & sports (e.g. jewelry, biking)

* Custom parts (e.g. classic car parts, surgical tools)

<figure><img src="image_5.png" /><figcaption>Al - heat exchanger</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>Al - valve</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Inco625 - turbine</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>316L - prosthesis</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>316L - heat sink</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>316L - valve</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>CuCrZr - textured pipe</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>Fe-Si - Slice of rotor</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>HEA - Jet engine bracket
+ lattice structure</figcaption></figure>
# AM technologies

* 7 main types of AM technologies

<figure><img src="image_14.png" /></figure>

<figure><img src="image_15.png" /></figure>

<figure><img src="image_16.png" /></figure>

<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /></figure>

<footnote n="1">¹A. Mazurchevici et al., DOI:10.5604/ijems.v27i2.45920</footnote>
# SLM principle

* First, desired parts are drawn with CAD and transferred layer by layer to the SLM tool

* Powder (base material) spread with a roller or a scrape to obtain a powder bed

* Powder bed densifying by fusing it locally with a laser according to desired shape

* Layer by layer, more powder is added, and the part is built

* After the printing, powder not fused is removed from the part with a brush, and then the part is cut from the tray

<figure><img src="image_19.png" /></figure>

Source: What is additive manufacturing? | GE Additive

<figure><img src="image_20.png" /></figure>
# SLM principle

* With SLM, only a small zone at the same time brought to fusion temperature

* Melt pools (melted zones) typically 100 µm wide

* High thermal gradients are present in their periphery. These melt pools solidify quickly, and this solidification happens with a preferential direction, leading to anisotropy within material

<figure><img src="image_21.png" /></figure>

Source: Kotadia et al. A review of Laser Powder Bed Fusion Additive Manufacturing of aluminum alloys: Microstructure and properties, 2021
# Content

* What is additive manufacturing ?

* Additive manufacturing for thermoelectrics

* Additive manufacturing for thermoelectrics at CEA
# AM for Thermoelectrics

* Why additive manufacturing for TE materials ?

- to obtain materials with new microstructures (anisotropy) that could potentially improve their TE properties

- to simplify the manufacturing process (no cutting step, less material losses, etc.) leading to save process time and decrease the cost

- the possibility to manufacture complex shapes at both materials and devices levels: shapes more suited to heat/cold sources, better TE module integration and so better efficiency

<figure><img src="image_22.png" /><figcaption>Example of unusual shape for TE device obtained by SLM (steel material)</figcaption></figure>
<figure><img src="image_23.png" /></figure>

# AM for Thermoelectrics

* Additive manufacturing of TE materials:

* First studies around additive manufacturing of TE materials in 2015

* Most are about $Bi_2Te_3$

* Mostly by Selective Laser Melting (SLM) (or LPBF - Laser Powder Bed Fusion)

<figure><img src="image_24.png" /></figure>

→ Very recent topic with few papers and groups involved

<figure><img src="image_25.png" /></figure>
Bi₂Te₃ by SLM¹

* Two main groups working on Bi₂Te₃ by SLM: one in USA and one in China

* Radio-frequency plasma high-energy spheroidization system (RFPs) applied for the preparation of p-type Bi₀.₅Sb₁.₅Te₃ and n-type Bi₀.₅Te₂.₇Se₀.₃ spherical powders, then Bi₂Te₃-based bulk material forming process performed by using the SLM printing system (Ampro SP100)

<figure><img src="image_26.png" /></figure>

<figure><img src="image_27.png" /></figure>

→ higher ZT in in-plane direction than cross-plane direction
(in agreement with SoA)

→ high ZT compared to SoA (SPS) due to a low size of grains
(in the range of several hundred nm to 1µm) decreasing λ
Bi₂Te₃ by SLM¹

* Manufacturing of Bi₂Te₃ half-rings-based TEG

* Use of copper electrodes and half-rings bonded on an alumina tube employing silver paste

* Test employing a homemade hot-water circulation system

* Maximum output voltage of 86 mV and an output power of 134 mW were achieved for a maximum temperature difference of 38.9°C.

* Output power density reached 65.42 mW.cm⁻²

<figure><img src="image_28.png" /></figure>
Bi₂Te₃ by SLS¹

* Powders prepared by ball milling bulk p-type Bi₀.₅Sb₁.₅Te₃, then SLS processes were performed using a XJRP SLS400 3D printer

<figure><img src="image_29.png" /><figcaption>(A) Photo image of long square block with a size of 12 mm by 3 mm by 2 mm, (B) cylinder sample with a diameter 12.7 mm and thickness of 2 mm, (C) SEM image showing micro pores, (D) SEM image showing nano pores.</figcaption></figure>

→ high ZT (up to 1.29) compared to SoA (SPS) due to porosity induced by the manufacturing method

<figure><img src="image_30.png" /></figure>
# HMS by SLM¹

* Material: MnSi₁.₇₅

* Preparation: material synthetized and sintered directly from ball milled manganese and silicon by SLM

* Energy dose of 91 J/cm² allowed to obtain the MnSiγ phase and its sintering

<figure><img src="image_31.png" /></figure>

Optical micrographs of the surface of the sheet samples made under various LPBF energy doses (J/cm²)

<figure><img src="image_32.png" /></figure>

SEM of (a) ball milled precursor powder (Mn and Si) and (b) Sample B manufactured by LPBF

<figure><img src="image_33.png" /></figure>

<figure><img src="image_34.png" /></figure>
# Half-Heusler by SLM¹

* Material: n-type ZrNiSn

* Preparation: Zr, Ni and Sn powders thoroughly mixed, cold-pressed then prepared by Self-propagation High-temperature Synthesis (SHS), and finally manufactured by SLM

<figure><img src="image_35.png" /><figcaption>(a) Images of the SLM-processed ZrNiSn on the Ti substrate (top view); (b) side view of the structure; (c) SEM image of the surface of SLM-processed ZrNiSn; (d) SEM image showing the interface between ZrNiSn and Ti highlighted by the red dashed line; (e)–(h) EDS elemental maps of the green rectangular area in (d)</figcaption></figure>

<figure><img src="image_36.png" /></figure>

→ During the SLM processing of ZrNiSn, a small amount of Sn has appeared as a secondary phase, leading to lower ZT (0.39 at 873 K)

<figure><img src="image_37.png" /></figure>

<figure><img src="image_38.png" /></figure>

<figure><img src="image_39.png" /></figure>
Skutterudite by SLM¹

* Material: n-type CoSb<sub>2.85</sub>Te<sub>0.15</sub>

* Preparation: powder of CoSb<sub>2.85</sub>Te<sub>0.15</sub> prepared by (SHS) and served as the raw material for the SLM process

<figure><img src="image_40.png" /></figure>

<figure><img src="image_41.png" /></figure>

<figure><img src="image_42.png" /></figure>

<figure><img src="image_43.png" /><figcaption>(a) SEM image of a cross section of the SHS-SPS sample. (b) SEM image of the as-prepared SHS-SLM sample. (c) SEM image of the SHS-SLM sample annealed at 450°C for 4 h; (d) the same as panel c but magnified, showing clearly the presence of a microcrack</figcaption></figure>

<figure><img src="image_44.png" /></figure>

<figure><img src="image_45.png" /></figure>

→ Presence of micro cracks leading
to low ZT values

<figure><img src="image_46.png" /></figure>
# Content

* What is additive manufacturing ?

* Additive manufacturing for thermoelectrics

* Additive manufacturing for thermoelectrics at CEA
# TE materials – 3D Technology

* Why developing TE technology by AM at CEA-Liten ?

1) CEA works on TE technology for 20 years

2) CEA works on AM technology (metal) for 7 years

→ Idea to combine both technologies proposed 4 years ago

→ First studies started at CEA-Liten 2,5 years ago

→ Very recent developments

* What materials to develop ?

→ Two materials chosen: SiGe and $Bi_2Te_3$

* What AM tool to use to manufacture these materials ?

→ ProX200 (1064 nm wavelength laser with a 70 µm spot diameter) with stainless steel plate

<figure><img src="image_47.png" /></figure>

Picture of ProX200 used at CEA to develop TE materials
# SiGe by AM

* Why SiGe ?

1) SiGe is a non-toxic, green and relatively abundant material

2) SiGe is a good TE material for high temperatures range (600°C-1000°C) making this material compatible with our applications targeted in the future (Radioisotope TE Generators (RTG), wood/pellet stoves, industrial applications, etc.)

3) both p- and n-types can be easily obtained by doping (boron and phosphorus, respectively) with the same thermal expansion coefficient making easier their integration in a device

4) SiGe is a well-known TE material making comparison of results easy to perform with standard references
# SiGe by AM

* First buildings of N-type SiGe parts<fnref n="1" />

<figure><img src="image_48.png" /></figure>

<figure><img src="image_49.png" /></figure>

<figure><img src="image_50.png" /></figure>

<footnote n="1">¹ M. Baudry et al., Materials Science & Engineering B 298 (2023) 116897</footnote>
# SiGe by AM

* SEM images (as built)<fnref n="1" />

<figure><img src="image_51.png" /></figure>

<figure><img src="image_52.png" /></figure>

<footnote n="1">¹ M. Baudry et al., Materials Science & Engineering B 298 (2023) 116897</footnote>
# SiGe by AM

* EDS map (as built - top view)<fnref n="1" />

<figure><img src="image_53.png" /></figure>

→ Ge & P segregation at grain and sub-grain boundaries

→ Phosphorus tend to group in clusters, limiting its role as doping element

→ Coherent with literature

→ Annealing to perform

<figure><img src="image_54.png" /></figure>

<figure><img src="image_55.png" /></figure>

<footnote n="1">¹ M. Baudry et al., Materials Science & Engineering B 298 (2023) 116897</footnote>
# SiGe by AM

* Thermoelectric properties<fnref n="1" />

<figure><img src="image_56.png" /></figure>

→ Low ZT (one decade below) due to a low electrical conductivity

→ More details with presentation of Maxime Baudry

<figure><img src="image_57.png" /></figure>

<footnote n="1">¹ M. Baudry et al., Materials Science & Engineering B 298 (2023) 116897</footnote>

<footnote n="2">² D.M. Rowe, Handbook of thermoelectrics, 1995</footnote>
# SiGe by AM

* Optimize SiGe material process leading to a decrease of cracking and an increase of TE properties

→ Micro segregation

<figure><img src="image_58.png" /></figure>

→ Solution: activation annealing

→ Development performed in the framework of ANR project FASTE (Dec 2022 – Nov 2025)

→ Thermal induced cracking

<figure><img src="image_59.png" /></figure>

→ More detailed information with Maxime's presentation

→ Solutions: use of heating build plate and integration of nucleating agents (nanoparticles)
# Bi₂Te₃ by AM

* Why Bi₂Te₃?

1) Bi₂Te₃ is the best TE material at room temperature (300K-550K) and even if a lot of studies on materials has been performed to find a competitive successor to this material, it is clear that no candidate has still emerged

2) both n- and p-types can be easily obtained by doping (selenium and antimony, respectively) with the same expansion coefficient making easier their integration in a TE device

3) all current TE commercial devices use Bi₂Te₃ as active material, it will be easier to enter in this market and to propose TEG for our targeted applications: autonomous sensors supply, batteries charger, etc.

4) Bi₂Te₃ is the most well-known TE material, making comparisons of results with standard references easy to perform

<figure><img src="image_60.png" /><figcaption>n-type Bi₂Te₃ materials obtained by SLM</figcaption></figure>
# Bi₂Te₃ by AM

* Microstructure characterization

<figure><img src="image_61.png" /></figure>

EBSD and SEM micrographs in the build direction of the sample

→ Anisotropy orientation

→ Columnar structures along Building Direction (BD)

→ Cracking along BD
# Bi₂Te₃ by AM

* Cracking microstructure

<figure><img src="image_62.png" /><figcaption>Cross-section view SEM microstructure of the sample cut in half.</figcaption></figure>

<figure><img src="image_63.png" /></figure>

→ To prevent hot cracking: a nucleating agent (for example SiC, the most widely used in the literature) could be added

<figure><img src="image_64.png" /></figure>

<footnote n="1">¹ J.-M. Drezet & al.« Fissuration à chaud : des alliages organiques aux superalliages », http://dx.doi.org/10.1051/meca:2004041, vol. 5, (2004) NTE2023</footnote>
# Bi₂Te₃ by AM

* Chemical analysis (by ICP-OES - Inductively Coupled Plasma Optical Emission Spectroscopy)

<table><thead><tr><th rowspan="2">Sample</th><th colspan="3">% molar</th><th rowspan="2">Composition</th></tr><tr><th>Bi</th><th>Te</th><th>Se</th></tr></thead><tbody><tr><td>Powder</td><td>40</td><td>54</td><td>5,9</td><td>Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub></td></tr><tr><td>SLM sample</td><td>44</td><td>50</td><td>5,6</td><td>Bi<sub>2</sub>Te<sub>2.5</sub>Se<sub>0.28</sub></td></tr></tbody></table>

Te loss:

<figure><img src="image_65.png" /></figure>

8%

→ Vaporization of tellurium and selenium

→ Wrong phase synthesized

→ XRD analyses performed but results do not allow to determine which phases are presents

→ Samples must be observed by TEM

<figure><img src="image_66.png" /><figcaption>Phase diagram of the bismuth-tellurium binary system</figcaption></figure>
# Bi₂Te₃ by AM

* TE properties

<figure><img src="image_67.png" /></figure>

→ Low ZT values
due to wrong phase
and crackings
# Conclusions

* AM is an emerging technology for thermoelectrics enabling to bring new approach to design and manufacture TE materials and devices

* Main advantages of AM:

- possibility to obtain new microstructures (anisotropy) that could potentially improve TE properties

- simplifying of the manufacturing process (no cutting step, less material losses, etc.) leading to save process time and decrease the cost (→ will be studied during FASTE project)

- possibility to manufacture complex shapes at both materials and devices levels

* Main research papers dedicated to Bi₂Te₃ materials with potential high ZT values

* At CEA: - SiGe parts have been manufactured for the first time

- Cracks issues for both SiGe and Bi₂Te₃

- Focus on SiGe development

* Main limitations of SLM:

- powder properties (grains size, sphericity, flowability, laser absorption, etc.)

- powder quantity (large quantity needed)

- no 3D tool specific for semiconductor materials : lot of work to develop adapted process flow (laser power, speed, hatch, etc.)
Acknowledgments

• Guilhem Roux, Maxime Baudry and Marine Barrabé

* The research leading to some of these results has been performed within the FASTE project and received funding from the ANR (ANR-22-CE50-0021)

anr
agence nationale
de la recherche

FASTE"""
<figure><img src="image_68.png" /></figure>

liten

<figure><img src="image_69.png" /></figure>

Thank you for your attention

Contact: [guillaume.savelli@cea.fr](mailto:guillaume.savelli@cea.fr)