What is negative thermal expansion? ALLVAR Alloys.

Negative Thermal Expansion

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What is Negative Thermal Expansion?

Thermal expansion refers to a material’s natural increase in size with increasing temperature. While all other metals in the world expand with increasing temperature, ALLVAR Alloys are designed to shrink with increasing temperature. This shrinking while heating is known as a negative thermal expansion (Negative CTE).

This revolutionary property can be used to compensate for the expansion or contraction of other materials in the world’s most demanding thermal stability applications. Spaceborne telescopes, high performance optical assemblies, and ultra-precision equipment are a few of the applications that require enhanced stability and performance when operating under shifting thermal environments.

Negative CTE alloys can be used as compensating elements or metering structures to passively athermalize optics or create ultra stable struts for telescopes. Outside of its optics applications, negative CTE enabled washers or spacers can be used to maintain a constant-force load across a wide temperature range.

How do Negative CTE ALLVAR Alloys compare to other alloys?

Property	Units	ALLVAR Alloy	Invar	304 Stainless Steel	6061 Aluminum	Titanium 64
Property	Units	ALLVAR Alloy 30	INVAR	304 Stainless Steel	6061 Aluminum	Titanium 6Al4V
CTE Range @20°C	(ppm/°C)	-30	1.6 to 6	17.3	23.6	9
Max Operating Temperature	(°C)	100	200	870	120	540
Yield Stress	(MPa)	405	276	215	55	828
UTS	(MPa)	800	448	505	124	895
Elastic Modulus	(GPa)	75	141	193	68.9	113.8
Density	(g/cc)	5.08	8.1	8.0	2.7	4.42
Thermal Conductivity	(W/m·K)	8.88	10.15	16.2	180	6.6

What type of technologies does Negative CTE ALLVAR Alloys enable?

ALLVAR Alloys are the only materials in the world that have a negative coefficient of thermal expansion. Our alloys are unrivaled in their capacity to athermalize a wide range of systems, leading to improved performance, reduced lead time, and reduced costs. Keep scrolling to learn more!

Athermalization of Optics using NTE Spacers

ALLVAR has a variety of commercially off-the-shelf (COTS) and custom NTE Spacers that help maintain optomechanical alignment and improve performance of optics, including:

Refractive Optics
Head mounted systems
Military & Aerospace optics
Augmented and virtual reality (AR/VR) systems
Free space optical systems
Reconnaissance optics

Ultra Stable Struts for Precision Systems

Have a metering application? ALLVAR’s Ultra-Stable Struts can solve thermalization issues in:

Telescopes and Reflective Systems
Satellites
Spacecraft
Ultra-precision systems

Constant Force Load Washers

ALLVAR offers a wide range of washers that can counteract the force and dimensional changes experienced during extreme temperature cycling. Utilize these revolutionary washers to:

Tackle CTE mismatch in extreme environments
Increase reliability of components in cryogenic systems, scientific instruments, precision machinery, and energy industries
Maintain constant force load in industrial seals and pre-loaded bolts
Solve thermal mismatch in liquid natural gas transport

Custom Negative Thermal Expansion Products or Components

The negative thermal expansion of ALLVAR Alloy 30 can be machined into custom products or components best suited for your specific product or project. Not sure if ALLVAR is a good fit for your project? Please contact us. We would be happy to discuss negative thermal expansion Alloy 30’s applicibility for your application.

Negative Coefficient of Thermal Expansion Washers

Negative CTE washers and spacers from ALLVAR compensate for the natural expansion and contraction of other materials with variations in temperature. ALLVAR washers/spacers combat other materials’ thermal displacement to keep constant force loads – no matter if it’s 80°C or -150°C. Athermalization of fastened assemblies can be achieved by eliminating the thermal stress induced by different materials.

WASHER / SPACER STARTER KIT
Kit includes:
• 12 hours of design and engineering time from Allvar engineers
• Set of washers (quantity depends on size of washers and the application)
Washers available in #2, #4, #6, and #8 sizes. Custom washer and spacer sizes are available

Meet the challenge of athermalization with the endless possibilities of ALLVAR.

Optical Tolerancing The CTE of the material used in an optical housing can add to an optics overall error budget. Gain some wiggle room with ALLVAR. ALLVAR Alloys can be used as a spacer to hone in on a specific desired CTE allowing you to shift that error budget to optical tolerancing.

SWaP-C Challenges Need to create a smaller or lighter optic that still performs across a wide range of temperatures? Unlike current athermalization solutions, ALLVAR Alloy’s negative thermal expansion allows housings to be smaller, lighter, and athermal.

Maintaining performance at temperature Is your system performing well at ambient temperature, but not across its full operating temperature range? Get that performance under control with ALLVAR Alloys. ALLVAR Alloys are designed to keep systems from bolted joints to large metering structures performing at their best, regardless of temperature.

Component CTE Mismatch Do individual components of your assembly consist of materials with different thermal expansion properties? ALLVAR Alloys compensate for this mismatch with their unique thermal expansion; they grow while other materials shrink.

CTE Control Add a new tool to your design toolbox. ALLVAR Alloy 30 enables designers to create a specific tailored CTE value by combining negative thermal expansion ALLVAR Alloys with positive thermal expansion materials to hone in on a desired CTE target.

Cryogenics Maintaining tight bolts is tough in cryogenic systems due to thermal mismatch. ALLVAR Alloy 30 washers were created to combat this specific problem. Ensure your fastened assemblies are consistently tight from ambient to cryogenic temperatures.

Narrow safety margins Achieving safety margins in bolted joints is a tough challenge when specific (or tight) margins have to be maintained across a wide range of temperatures. ALLVAR Alloy’s negative thermal expansion washers can help maintain pre-load with narrow safety margins across a wide range of temperatures.

Reliability Thermal expansion mismatches can be the root cause of a wide range of issues, from fastener slip and fatigue to outright failure. Fastener slip is caused by a loose bolt that doesn’t have enough clamp force to hold a joint together. ALLVAR Alloy washers can help prevent loss of clamp force and prevent fastener slips through its near-zero thermal expansion properties. Another issue that can arise is fastener fatigue, where components fatigue as they repeatedly become more and less stressed through thermal cycles. ALLVAR Alloys help counter this issue by keeping consistent stress across temperatures. Get control of your thermal expansion mismatches for more reliable performance with ALLVAR Alloys.

Vibration While vibration can cause the loosening of bolts on its own, the effect can be worsened by differential thermal expansion of components. ALLVAR Alloys can lessen these effects by creating a constant clamping force and maintaining a tight joint.

Do you offer Negative CTE alloys at temperatures higher than 100 degrees C?

Yes. Additional alloys that can withstand higher temperature ranges were developed as part of a NASA SBIR grant. If you are interested in a higher temperature capable alloy, please contact us with more details on your application and desired temperature ranges so we can find the best athermalization solution for you.

Where can I learn more about your alloys?

You can start by visiting our FAQ page and our video library for demonstrations and discussions. Our News page also has information about our work to develop negative thermal expansion enabled technologies like ultra-stable struts, athermal optics, and constant-force load washers. You can also contact us for more information.

You can also find more information on ALLVAR Alloy 30’s matweb.com page or read published SPIE proceedings on SPIE’s Digital Library.