ASTRONOMICAL+SPIE. TELESCOPES
INSTRUMENTATION

June 16-21 2024 Yokohama, Japan

Unlocking the potential of non-ferromagnetic
Invar-type alloys in space exploration

Hiromichi T. Fujii*, Shingo Matsumura, Naoki Sakaguchi, Haruyasu Ohno, Kotaro Ona
Shinhokoku Material Corp.
* fujii@shst.co.jp

新報国マテリアル株式会社
SHINHOKOKU MATERIAL CORPORATION

Outline Background and motivation✓ Introduction of low thermal expansion alloys✓ Non-ferromagnetic Cr-based Invar-type alloys

 Experimental procedure Results and discussion✓ Achieving low thermal expansion characteristics throughthe addition of Fe to Cr✓ Control of Néel temperature by Mn addition✓ Impact of additive elements on thermal expansion characteristics✓ Magnetic properties of Cr-Fe-Mn alloy Conclusions

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Customized Invars for specific temperature applications
 Customized super Invar✓ Suitable for cryogenic temperatures(down to −100ºC)✓ Extremely low thermal expansion (< 0.015 x 10−6/K)✓ Dimensionally stable over years World’s only customized stainless Invar1, 2✓ Zero-expansion✓ Breaking new ground with the world’s first zeroexpansion stainless Invar (Patented)

 Challenges✓ Dimensional change under a magnetic field due tolarge magnetostriction

A range of low thermal expansion alloys is available across a wide temperature
spectrum. (Coefficient of thermal expansion: Adjustable from 10-7 to 10-5 /K)

1 H.T. Fujii et al., Proc. SPIE, 11451 (2020), 1145118.

2 H.T. Fujii et al., Proc. SPIE, 12188 (2022), 1218806.

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Non-nonferromagnetic Cr-based Invar-type alloy Challenges associated with magnetism✓ Dimensional changes due to magnetostriction•Semiconductor manufacturing equipment✓ Magnetic noise•Electron microscope•

Medical diagnostics✓ Magnetic induction•

Electrolytic refining furnace•

Power transmission facilities

1 K. Fukamichi and H. Saito, Phys. Stat. Sol. (a), 10 (1972), K129-131.

Thermal expansion curves of Cr-Fe-Mn alloys1. For comparison, thecurves of typical Invar 36 and pure Cu are also shown.

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Purpose

By conducting a detailed analysis of the Cr-Fe-Mn non-ferromagnetic Invar-type alloy's
thermal expansion behavior and magnetic response, we aim to enrich scientific understanding
and pave the way for new industrial applications of non-ferromagnetic alloys with minimalthermal expansion.

 Research issues✓ Achieving low thermal expansion characteristics through the addition of Fe to Cr✓ Control of Néel temperature by Mn addition✓ Impact of additive elements on thermal expansion characteristics✓ Magnetic properties of Cr-Fe-Mn alloy

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Experimental Sample preparation✓ Materials: Cr-Fe, Cr-Fe-Mn and Cr-Fe-Mn-RE✓ Methods: Arc melting

 Measurement of thermal expansion
characteristics✓ Precise dilatometer with furnaceand cooling bath
✓ Temp. range: 120 – 470 K✓ Heating rate: 5.0 K/min

 Evaluation of magnetic properties✓ Vibrating sample magnetometer✓ Specimen dimension: 5 mm x 5 mm x 1 mm

✓ Magnetic field direction: Parallel to the plate

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Results and discussion

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Manifestation of low thermal expansion characteristics
 Anomalous thermal expansion in Cr-based alloys✓ Distinct inflection points, known as Néeltemperature (TN), are revealed by the Fe addition✓ Low thermal expansion characteristics areobserved below TN✓ TN is lower than 0ºC and decreases with increasing
Fe contentLow
thermal expansion

 Nature of low thermal expansion

Néel temp.

✓ Reduced lattice vibrations due to stronger
antiferromagnetic ordering below TNThermal expansion curves obtained from pure Cr and Cr-Fe alloys. For comparison,previously reported curves by Fukamichi et al.1 are also included.

1 K. Fukamichi and H. Saito, AIP Conf. Proc., 17 (1974), 45-55.

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Potential applications and limitations of Cr-Fe alloys
 Applicable temperature range

Room temp.

✓ Measured TNs are good agreement with previous
data estimated by various methods✓ Cr-Fe alloys can be used as low thermal expansion
materials only below room temperature CTE estimated at specific temperatures
Material

CTE at each temperature [10−6/K]

150 K

200 K

250 K

300 K

350 Kpure Cr

4.39

5.83

5.63

3.81

8.62

Cr95Fe5

1.25

0.19

6.50

8.96

8.82

Cr90Fe10−1.43

7.45

7.82

8.44

9.07
The impact of Fe addition on the Néel temperature of Cr alloys, as determined fromthermal expansion measurements. For comparative purposes, the graph also
includes data previously estimated by various experimental1, 2.
1 K. Fukamichi and H. Saito, AIP Conf. Proc., 17 (1974), 45-55.

2 M.A. Mitchell and J.F. Goff, Phys. Rev. B, 5 (1972), 1163-1170.

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Tailoring thermal expansion characteristics of Cr-Fe-Mn alloys

CTE = 0.94 x 10−6/K(< 1.2 x 10−6/K of Invar)

Drastic change withincreasing Mn content

1.2 x 10−6/K (Invar)

Thermal expansion curves obtained from Cr-based Invar-type alloys with varying Mn contents and the impact of Mn content on the average CTE between
273 and 350 K in Cr-based Invar-type alloys. The average CTE values were derived from the thermal expansion curves.

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Impact of rare earth elements on thermal expansion
 Role of rare earth elements✓ Cr-based alloys face challenges in formability,
hindering mass production use✓ Incorporating rare earth elements has shownpromise in improving machinability Change in thermal expansion behavior✓ Overall thermal expansion behavior of the alloy
remains consistent even with the addition of rareearth elements, preserving its fundamental thermalproperties

Slight volume contraction andincrease in the Neel temp.

Thermal expansion curves obtained from Cr-based Invar-type alloys with andwithout rare-earth elements.

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Magnetic properties of Cr-based Invar-type alloy Magnetization curve✓ Magnetization is nearly zero
✓ Magnetostriction would be significantly lower
compared to standard Invar 36

Minimalmagnetization

 Magnetic propertiesMagnetic properties

Cr-based Invar

Invar 36

Residual magnetization [T]

3.7 x 10−6

3.5 x 10−2

Permeability [H/m]

6.3 x 10−11

9.4 x 10−6

Magnetization curves obtained from Cr-based Invar and Invar 36 using
vibrating-sample magnetometer (VSM).

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Conclusions

1.

Incorporating Fe into Cr significantly reduces thermal expansion below the Néel temperature, making
these alloys suitable for cryogenic applications.

2. The addition of Mn further enhances these properties by increasing the Néel temperature, thereby
extending the low thermal expansion characteristics to temperatures closer to room temperature.
This makes Cr-Fe-Mn alloys promising candidates for applications requiring dimensional stability
over a broader temperature range.
3. Magnetic measurements confirmed the non-ferromagnetic nature of Cr-based Invar-type alloys,
which exhibit minimal magnetization and magnetostriction, making them ideal for high-precisionapplications where magnetic neutrality is essential.

Our comprehensive analysis highlights the potential of Cr-Fe-Mn alloys as superior alternatives toconventional Invar alloys, particularly in fields such as aerospace, precision instrumentation andother engineering applications requiring minimal thermal expansion and magnetic interference.

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THANK YOU
新報国マテリアル株式会社
SHINHOKOKU MATERIAL CORPORATION

Hiromichi T. Fujii+81-49-242-1955
fujii@shst.co.jp
www.shst.co.jp