Causes of the surface damage:
parked head is detached from the shoulder. Heads arm is scratching the surface of the plate. If the hard drive does not have a self-diagnosis and the software will not detect a lack of HD's head, the engine will be rotating until the power supply is disconnected. It is possible to complete cut off the plate from the engine;
attempts to start knocking hard drive can end up with tearing off the head and the introduction of the pressure on the plate. Consequences are just like above.;
head breaks off the plate as a result of a fall or impact, the consequences like above.;
High temperature heats the plate to the Curie temperature;
flood or getting the fluid into the hard drive contaminates the plates. It usually does not cause permanent damage.
Physical damage of the surface often causes immediate damage to the new added heads. Data recovery in such cases is the laborious copying another megabytes, changing damaged heads and struggling with bad sectors.