geheugenalloys

Geheugenalloys are metal alloys that can return to a pre-defined shape after deformation when exposed to a specific stimulus, typically heat or mechanical stress. They are commonly referred to as memory alloys or shape memory alloys (SMAs) and operate through solid-state phase transformations.

The core mechanism involves a transformation between two solid phases, martensite and austenite. In the low-temperature martensitic state, the material can be deformed easily. When heated (or, in some cases, stressed beyond a threshold), it transforms to the austenite phase and recovers its original shape. Some SMAs also exhibit superelasticity, a stress-induced form of recovery that occurs near a transformation temperature without a temperature change.

Nickel-titanium (NiTi), known commercially as Nitinol, is the most widely used SMA, valued for its large recoverable strains and biocompatibility. Copper-based SMAs (such as Cu-Zn-Al and Cu-Al-Ni) and iron-based SMAs are used for specific applications, often where cost or working temperatures differ. Key properties include shape recovery, fatigue resistance, damping, and corrosion resistance (particularly for NiTi). Limitations can include fatigue life sensitivity, hysteresis in the transformation, processing complexity, and temperature dependence of behavior.

Processing and design involve tuning transformation temperatures through composition and thermo-mechanical treatment, as well as “training” the material to fix a reference shape. Applications span medical devices (stents, guidewires, orthodontic wires), actuators and couplings, aerospace and robotics, and niche consumer devices. Geheugenalloys continue to be developed to expand operating ranges, reduce costs, and improve reliability across industries.