Special materials demand special attention. When it comes to selecting the right material for high-performance applications, the choice often narrows down to two top contenders: Invar and Inconel. These two superalloys, each with its own unique set of properties, are widely used in various industries. But how do they stack up against each other? This article offers an in-depth comparison of Invar vs Inconel, outlining their key features, applications, and differences.
1. Introduction to Invar and Inconel
1.1 What is Invar?
Invar, generically known as FeNi36 (64FeNi in the US), is a nickel-iron alloy notable for its uniquely low coefficient of thermal expansion (CTE or α). The name Invar comes from the word invariable, referring to its relative lack of expansion or contraction with temperature changes. It is used to make extreme precision equipment such as scientific laboratory equipment, gauges, clocks, stencils, etc.
1.2 What is Inconel?
Inconel, on the other hand, is a trademarked word of Special Metals Corporation and it refers to a branch of high nickel superalloys that are resilient to corrosion and oxidation at elevated temperatures. It is predominantly used in the aerospace industry. Its hardness increases non-linearly during machining, wearing the tool disproportionately, hence it’s considered a tough material to machine.
2. Key Features: Invar vs Inconel
2.1 Key Features of Invar
Invar does not get hardened with temperature, but only with cold working. So, the hardness increase during machining is relatively lower. But, it does not make the material much easier to machine. It is softer than Kovar and thus it does not chip off. The tool plunges through. So, care must be exercised when machining
2.2 Key Features of Inconel
On the flip side, Inconel is extremely hard because it does not get any softer when the temperature rises. Cold working increases its hardness, making it difficult to machine, whereas metals like stainless steel get softer when the temperature rises, making it easier to cut.
3. Properties: Invar vs Inconel
3.1 Physical Properties of Invar
Invar has an extremely low thermal expansion nickel-ferrous alloy. It differs from Kovar in that it is a controlled expansion metal (designed to have the same coefficient of thermal expansion as borosilicate glass), whereas Invar is an extremely low coefficient of thermal expansion metal.
3.2 Physical Properties of Inconel
Inconel has a high-temperature coefficient of strength. It is resilient to corrosion and oxidation at elevated temperatures and does not get any softer when the temperature rises.
4. Machining: Invar vs Inconel
4.1 Machining Invar
Invar does not get hardened with temperature, but only with cold working. So, the hardness increase during machining is relatively lower. But it does not make the material much easier to machine. It is softer than Kovar and thus it does not chip off. The tool plunges through. So, care must be exercised when machining.
4.2 Machining Inconel
Machining Inconel is extremely hard because it does not get any softer when the temperature rises. Cold working increases its hardness, making it difficult to machine, whereas metals like stainless steel get softer when the temperature rises, making it easier to cut.
5. Usage: Invar vs Inconel
5.1 Usage of Invar
Invar is used to make extreme precision equipment like scientific laboratory equipment, gauges, clocks, stencils, etc.
5.2 Usage of Inconel
Inconel’s high strength to weight ratio is one of the reasons for this. But it is one of those properties that make Titanium difficult to machine. Titanium is increasingly replacing aluminium as the most popular for aerospace applications.
6. Corrosion Resistance: Invar vs Inconel
Both Invar and Inconel have excellent corrosion resistance properties. However, Inconel has a slight edge as it remains resilient to corrosion even in elevated temperatures.
7. Temperature Resistance: Invar vs Inconel
While Invar has an extremely low coefficient of thermal expansion, Inconel stands out for its high-temperature coefficient of strength. Inconel does not soften when the temperature rises, which makes it more suitable for high-temperature applications.
8. Strength: Invar vs Inconel
In terms of strength, Inconel outperforms Invar. The high strength-to-weight ratio of Inconel makes it a popular choice for aerospace applications.
9. Cost Effectiveness: Invar vs Inconel
In terms of cost-effectiveness, Invar is generally cheaper than Inconel. However, the final cost may vary depending on the specific requirements, quantity, and supplier.
10. Availability: Invar vs Inconel
Both Invar and Inconel are widely available in different forms such as round bars, flat bars, plates, sheets, etc. These materials can be sourced from various suppliers globally.
11. Industries They Serve: Invar vs Inconel
Invar is widely used in the manufacture of scientific laboratory equipment, gauges, clocks, stencils, etc. On the other hand, Inconel, due to its high strength and temperature resistance, is predominantly used in the aerospace industry.
12. Conclusion: Invar vs Inconel
Both Invar and Inconel are unique and versatile materials with a plethora of applications. The choice between the two should be based on the specific requirements of the particular application. Invar is ideal for applications where a low coefficient of thermal expansion is required. On the other hand, Inconel is perfect for applications that demand high strength and temperature resistance.
