Here's a chart taken from the Rosenstiel book. Any one of these alloys can be used for PFMs.
Most of the time you don't know what alloy the lab is using, specifically, however, you can request certain categories... i.e. 1. High gold, high noble alloy (Jelenko O = $$$$), 2. Moderate gold, high noble alloy (Olympia = $$$), 3. Silver-Palladium type Noble alloy (Superstar = $$), 4. Base metal (Rexillium = $).
Most practices and dental schools use category 3. In my own mouth, category 1 or 2, depending on the restoration needs. Stay away from type 4 if you can... but it works in certain situations.
See the following chart: