All of Bisco's adhesives provide high adhesion to metal and would be appropriate for this scenario. Our adhesive instructions will cover the steps of this indication.
Alternatively, you might want to consider Bisco's INTRAORAL REPAIR KIT. This would provide you with all the required components to complete any type of intraoral repair. The use of composite alone often times will not successfully block the dark metal hue, the opaquer in the kit allows you to do this without creating bulk and gives you a bit more flexibility in choosing a composite shade for the repair. The entire kit costs less than a bottle of adhesive. This link contains a technique card that shows the steps for a PFM repair.