Wings of Redemption
Reading the rules literally, when casting the Ironwood spell, the wooden object (material component) is destroyed and an identical ironwood version materializes in its place. Thus, when the duration of the spell ends, you are left with nothing.
However, in this case, logic applies. The material component (wooden object) is transmuted into the ironwood object, and transmutes back into normal wood at the end of the spells duration (1 day/level). This is supported by the fact that the spell is a Transmutation spell and not a Conjuration (Creation) spell.
This basically means that you only have to Transmute Metal to Wood one Chain Shirt and then keep casting Ironwood on it, rather than needing to get a totally new chain shirt at the end of the duration every time. As a side note, it also prevents you from evaporating an enemy’s bow by using Ironwood and then dismissing the spell!