particularly plastic deformation of the surface layer is accomplished at room temperature which causes strain hardening and a cold worked distorted microstructure although a shot peening source 14 is illustrated in fig2 a other alternatives may include forging swaging cold rolling coining and hammering subsequent to the metal deformation is the application of heat which will induce recrystallization leading to a new fine grained strain free material at the surface of the block 10 the grain refinement resulting from this method corresponds to a superplastic surface condition the refined grain microstructure resulting at the end of the present method is schematically illustrated at the surface 18 by reference numeral 20 in a preferred embodiment of the present invention the metal deformation of the block surface is produced by shot peening source 14 which directs a flow of shot at the surface 18 of the plate in order to move the energy source 14 relative to the plate surface 18 it is possible to utilize a conventional numerical control device 22 such as is prevalently utilized in robotics and machine tool controls in the case of a flat block 10 as shown in fig2 a the control device need move the energy source 14 at a constant speed across the surface 18 so that each point receives substantially the same amount of shot from the source alternatively the block 10 may be moved relative to a stationary source 14 this would typically involve a movable table not shown upon which the block rests the table would be moved in the x y plane by a numerical control device such as 22 this will result in a desirable uniform grain reduction along a surface layer thus in such an application the shot source and plate.