I _think_ they're often nitinol, i.e., shape-memory metal. Nitinol can be hot-formed, cooled, then formed a further limited amount. When reheated, they will return to their hot-formed shape.
It did, so slow clap for the engineers for saving a very expensive science experiment remotely from billions of miles away. well done.
Back on topic, the release mechanism jams every now and again across the probes sent to deep space. Hope the engineers are given the window of opportunity to solve this category of problem once and for all by business-ops. The release of the JWST antenna while at the moment of sparkly reflections in the sunshine looked real strong.