Laser Peening without Coating as a Surface Enhancement Technology

Laser peening without coating (LPwC) is an innovative surface enhancement technology, which imparts compressive residual stress without any surface preparations. Materials were peened in aqueous environment with laser pulses of about 100 mJ from a Q-switched and frequency-doubled Nd:YAG laser. Surface roughness of the materials somewhat increased due to ablative interaction. Compressive residual stress nearly equal to the yield strength of the materials appeared at the surface after LPwC in spite of the possible heat effect by direct laser irradiation to the materials. The depth of the compression reaches 1 mm or more from the peened surface. High-cycle fatigue properties were evaluated through rotating-bending or push-pull type testing for an austenitic stainless steel (SUS316L), a titanium alloy (Ti-6Al-4V) and a cast aluminum alloy (AC4CH). LPwC significantly prolonged the fatigue lives despite the increase in surface roughness. Accelerating stress corrosion cracking (SCC) tests showed that LPwC completely eliminated SCC susceptibility of sensitized austenitic stainless steels, nickel-based alloys and their weld metals. LPwC has been utilized to prevent SCC in Japanese nuclear power reactors since 1999.