A method and apparatus for improving the properties of a material of a workpiece
by laser shock peening in which an overlay which is opaque to a laser beam, and
an overlay which is translucent to said laser beam, are applied to a surface of
a workpiece. The translucent overlay being applied on top of and over the opaque
overlay. A laser beam is then directed at the said surface to which the overlays
have been applied to vaporize the opaque overlay and laser shock peen the surface
of the workpiece to produce a region of compressive residual stress in said surface.
The overlays and the laser beam being applied concurrently, in a single operation,
as the surface of the workpiece is traversed so that as each point on the surface
to be treated is traversed the opaque overlay, translucent overlay, and laser shock
peening are applied sequentially to that point. The opaque overlay is preferably
an ink layer which is applied by printing on the surface. The apparatus, which
in particular is arranged for carrying out this method, comprises the means for
applying the overlays and for directing the laser beam at the surface all mounted
upon a common tool head.
