In the space opera concept story I'm working on, the underdog faction develops/discovers several technologies and resources that help them turn the tide against the enemy. One of these discoveries is a "living" metal (I was gonna call it "Animite" but googling it, the name has been used for to many fantasy metals already - new name suggestions will be appreciated). While not being sapient, or even sentient, it does self repair by consuming other elements by contact. So cutting a slab in half, and feeding the two halves will eventually produce two wholes. While the replication process is far from fast, it does give vehicles in the field the ability to self repair with minimal equipment and resources, as well as supply a near infinite supply of usable metal.
Note: To keep the armour plates made of Animite from consuming the vehicle the plates are coated with a protective layer. When repairing a neutral foam is first injected into the hole to prevent the newly grown metal from making contact with the vehicle.
How could I make this plausible without too much hand wave? Maybe a symbiotic type of bacteria?