Assisted self-healing of fatigue damage in metals

Important results from the project

The purpose of the project is to investigate the possibility of applying various metallurgical processes that can eliminate or minimize fatigue damage in metallic materials after a period of use. Processes that can be described as assisted self-healing of fatigue damage in metallic materials. The results show that a very common material such as 316L has a very good ability to self-heal fatigue damage when using a specific heat treatment. The material not only regains its full fatigue life, but is in many cases even slightly better than in its original state.

Expected long term effects

One of the two materials studied showed a good ability for assisted self-healing if the right type of heat treatment is applied after obtaining a certain amount of partial fatigue damage. By utilizing this effect in connection with component remanufacturing or apply it at the regular service intervals, it would be possible to enable a more continuous and extended use of components in metallic materials and contribute to a more efficient remanufacturing process. This would be favorable from an environmental point of view and contribute to a more circular economy.

Approach and implementation

Two materials have been studied, a stainless steel 316L in both cold-deformed and solution-treated states, and a nickel base material of type Hastelloy X in solution-treated state. Smooth cylindrical test rods with ground and polished gauge section have been manufactured and tested. Various heat treatments have been applied to see how these affect the fatigue properties of the materials. The heat treatments have been done both directly on an untested condition but also after the material has received a certain amount of partial damage after interrupted fatigue testing.