Yield strength anomaly

In materials science, the yield strength anomaly refers to unusual materials wherein the yield strength (i.e., the stress necessary to initiate plastic yielding) increases with temperature. For the vast majority of materials the yield strength decreases with increasing temperature. The yield strength anomaly is also referred to as the yield stress anomaly.

Precipitation hardening superalloys exhibit yield strength anomaly over a considerable temperature range. For these materials, the yield strength shows little variation between room temperature and several hundred degrees Celsius. Eventually, a maximum yield strength is reached. For ordered intermetallics, this is usually the case at roughly 50% of the absolute melting temperature. For even higher temperatures, the yield strength decreases and, eventually, drops to zero when reaching the melting temperature, where the solid material transforms into a fluid.

The yield strength anomaly is exploited in the design of gas turbines and jet engines that operate at high temperatures, where the materials used are selected based on their paramount yield and creep resistance. Superalloys can withstand high temperature loads far beyond the capabilities of steels.