Confinement and absorption layer free nanosecond laser shock peening of tungsten and its alloy

Traditionally, nanosecond laser shock peening (ns-LSP) of metals requires an additional application of an absorption layer (black paint) and more importantly a confinement layer (typically water or transparent material) on the workpiece for introduction of compressive stresses. In this paper, we demonstrate for the first time, to the best of our knowledge, introduction of compressive stresses in pure tungsten and its alloy TAM7525 (75% tungsten and 25% copper) with-out any absorption and confinement layer for ns-LSP. Peak compressive stresses of -349 MPa and -357 MPa were meas-ured in pure tungsten and TAM7525, respectively, when a 0.25-cm2 area was irradiated by a Yb:YAG laser (1030 nm) operating at similar to 5 J, similar to 2 ns with circular polarization. These peak compressive stresses (without confinement layer) com-pare well to those with tungsten ns-LSP done with water as confinement layer at twice the energy at 10-ns pulse dura-tion. Furthermore, compared to femtosecond laser shock peening (fs-LSP) of aluminum at atmospheric pressure, the depth of compressive stresses recorded in tungsten and its alloy (similar to 7 times denser than aluminum) is nearly four times more in the case of confinement layer free nanosecond laser shock peening (CLF-ns-LSP).