Can a blow to the head with no loss of consciousness have any brain damage ?

Not likely: The brain is well cushioned in a pool of fluid surrounded by a tough bony shell. A heat hit with no loss of consciousnes and a lack of the dazing (called by coaches ringing your bell), is unlikely to have any demonstrable effects. Of course i assume this is isolated and you are not having repeated blows to the head. This is why athletes wear helmets.