Nimonic 90 Disc Springs: Performance Limits of a High-Temperature Creep-Resistant Spring Material

Nimonic 90 (DIN 2.4969) is a nickel-chromium-cobalt precipitation-hardened superalloy developed specifically for high-temperature strength and creep resistance.

Its room-temperature elastic modulus is approximately 220,000 N/mm², with a long-term service temperature limit of approximately 600°C. It is commonly used in high-temperature disc springs and turbine-related elastic components.

The alloy's high-temperature mechanical properties rely on precipitation strengthening. It demonstrates excellent creep resistance in the 600–700°C range.

However, engineering research has revealed an easily overlooked but important conclusion:

Creep data measured from raw-material tensile specimens cannot directly predict the stress-relaxation rate of finished disc springs.

A formed disc spring contains forming-induced residual stresses, a specific surface condition, a non-uniform stress distribution, a particular cold-working history, and a specific heat-treatment condition.

Testing has shown that under compression at 600–700°C, the load-loss rate of Nimonic 90 springs can be significantly higher than the theoretical value predicted from raw-material creep curves.

This is a critical risk that spring designers need to consider.

Applications and Limitations

Nimonic 90 is suitable for disc springs where high-temperature creep resistance and long-term static loading at elevated temperature are the primary performance requirements.

Compared with Inconel X-750, it has fewer engineering application cases in the nuclear power sector.

Even when Nimonic 90 is selected, high-demand applications should include dedicated stress-relaxation testing of the finished disc springs to verify actual spring performance. Material handbook data should not be directly applied.

At the same time, the basic disc spring geometry—including thickness, free height, and stacking configuration—continues to determine the fundamental stress level of the spring. Material selection cannot compensate for geometric design deficiencies.