If the military does a background check for a security clearance in order to be commissioned, will they be able to see a charge that has been expunged?

Typically a crimnal charge that has been expunged will not be made available for any public records. Criminal matters that have been expunged are still kept on record with the court system and prosecutors office, but a search of your State Police criminal database should not reveal a criminal conviction or criminal record if expunged.