Exploring the differences between Invar and ALLVAR Alloys
In the world of low thermal expansion alloys, Invar has been a cornerstone for precision engineering. This iron-nickel alloy is known for its low coefficient of thermal expansion. Now, ALLVAR Alloy 30 introduces a groundbreaking alternative with a negative CTE (Coefficient of Thermal Expansion). Unlike Invar, an iron-nickel alloy with uniform (isotropic) expansion, ALLVAR Alloy 30, a titanium alloy, contracts in one direction with heat.
Key Benefits of ALLVAR Alloy 30:
- Non-magnetic: Ideal for sensitive applications.
- Less Material Needed: Compensate for thermal mismatch with thinner washers or spacers.
- Lower density: Lighter than Invar alloys.
- Corrosion resistant: No coatings needed
- Improved Thermal Compensation Washers: 5x less mass and 3.1x thinner than comparable Invar-36 washers and spacers. Read how here.
As we say, “ALLVAR Alloy 30 is all the VAR that Invar isn’t.” Ready to find the right alloy? Contact our experts today!
Invar Alloys: History and Properties
In 1895, Swiss physicist Charles Guillaume discovered Invar, revolutionizing precision instruments. A chance observation of nickel-iron alloys led him to systematically investigate a whole series of alloys and les to this low CTE discovery. Its low CTE earned Guillaume a Nobel Prize in 1920. Over 130 years, Invar alloys evolved into forms like Invar-36, Super Invar, and Kovar. The alloy had a significant effect on scientific instruments and incandescent lightbulbs during Charles Guillaume’s life and had a major impact on the world around us ever since..
Invar’s isotropic CTE ensures consistent expansion in all directions. This property allows manufacturers to craft complex components with stable dimensions. However, it requires special handling to maintain its properties. Invar 36 is magnetic below its Curie temperture (230°C). Above this temperature it is nonmagnetic, but has a much higher CTE. Learn more about those properties here.
ALLVAR Alloy 30: A New Alternative to Invar
Researchers developed ALLVAR Alloys in 2011 to offer a range of thermal expansion solutions. Engineers designed ALLVAR Alloy 30 with a negative CTE of -30 ppm/°C along its length, allowing it to contract as temperature rises. In contrast to invar’s isotropy, this negative CTE is in the axial direction. It expands at +31 ppm/°C in diameter.
This unique property lets designers compensate for thermal expansion in assemblies. By adjusting the length of ALLVAR Alloy 30, you can achieve any CTE from -30 ppm/°C to the most positive material in your system. Learn more about ALLVAR applications.
CTE of Invar Alloys compared to ALLVAR Alloy 30
Controlled Thermal Expansion Alloy CTE Comparison
| Alloy | CTE at 25°C (ppm/°C) | Temperature Range |
|---|---|---|
| Invar-36 | 1.6 | -70 to 100°C |
| Super Invar | 0.720 | 25 to 96°C |
| Kovar | 5.2 | 25 to 200°C |
| ALLVAR Alloy 30 | -30 | Cryogenic to 100°C |
Machinability and Heat Treatments Vs. ALLVAR Alloy 30
Invar-36 requires stress-relieving treatments to ensure CTE stability. These treatments are a hidden factor that increase costs and production time. Its hardness causes rapid tool wear, making machining challenging. For further guidance, see Invar 36 Machinability Challenges | How To Overcome Them?
ALLVAR Alloys machine like a beta-titanium. With proper speeds, feeds, and a skilled machinist, it’s easier to work with than Invar. There are no special heat treatments required. Key considerations of machining ALLVAR Alloy 30 include:
- Flooding the cutting surface with coolant due to its maximum operating temperature of 100°C.
- Using a “pecking” technique when drilling.
Need custom parts? ALLVAR can help.
Operating Temperatures and Corrosion Resistance Vs. ALLVAR Alloy 30
Engineers should consider the operating temperature range. ALLVAR Alloy 30 performs well from cryogenic temperatures to 100°C. Its CTE performance cannot be guaranteed above 100°C.
The magnetic properties of Invar, Super Invar, and Kovar dictate their low thermal expansion. Therefore, they lose their low thermal expansion when cooling to colder temperatures or going above their Curie temperature. For example, Super Invar loses its low CTE properties at very low temperatures, while Invar-36 drifts from its low CTE outside a -70 to 100°C temperature window.
Invar corrodes easily if not handled properly, so components typically require nickel plating or other coatings to prevent corrosion during service. ALLVAR Alloys on the other hand have excellent corrosion resistant properties like other titanium alloys. ALLVAR Alloys can also be anodized and coated like other titanium alloys.
Should you use Invar or ALLVAR Alloys?
It depends on your application! Each alloy has its advantages for specific applications. In our post, Matching ZERODUR’s CTE with ALLVAR Alloy 30, the ALLVAR team details using both alloys in a design to achieve an ultra-stable strut with a near zero CTE.
If Invar’s low thermal expansion works and you need the same isotropic thermal expansion properties in every component direction, INVAR is likely better suited for your project. If your goal is to target thermal stability in one direction or compensate for thermal mismatch of dissimilar materials, consider using ALLVAR Alloy 30.
- Invar: Ideal for isotropic low CTE in all directions.
- ALLVAR Alloy 30: Perfect for compensating thermal mismatch in one direction
Still unsure which alloy is better for your project? We are here to help you find the right material for your next project. Contact us to determine which alloy is right for your project.
We are also happy to provide a spec-sheet with example CTEs across a wide range of temperatures or if you are interested in our experimental ALLVAR Alloys with higher upper operating temperatures.
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