A very interesting case. I was asked to recover information from the Seagate 7200.7 ST3160827AS. When inspecting it I noticed that disc was severely damaged.
You can see signs of pressure inside the hermetical zone (shown in the picture with arrows).
Deformation traces on the upper cover
The back side of fastening place of the spindle engine has marks of a hard blow. The blow was so strong that a platform was jummed together with the engine and the platter shaft.
View of HDD from the engine platform
One more angle shot
You can see marks of jamming in the inside of the disk upper cover
Inside of upper cover
The upper reading/recording head and the spindle engine shaft are deformed.
Inside the hermetical zone
The saddest thing about it is that plates, at least, the upper one, are bent. In the picture you can see that unruffled surface turned into "shagreen leather" and magnetic coating is jammed because the plate deformation.
Alas, but data recovery from such a disc is impossible.