Abstract
During conventional submerged laser peening, the impact force induced by laser ablation is used to produce local plastic deformation pits to enhance metallic material properties, such as fatigue performance. However, a bubble, which behaves like a cavitation, is generated after laser ablation, known as “laser cavitation.” On the contrary, in conventional cavitation peening, cavitation is generated by injecting a high-speed water jet into the water, and the impacts of cavitation collapses are utilized for mechanical surface treatment. In the present paper, a mechanical surface treatment mechanism using laser cavitation impact, i.e., “laser cavitation peening”, was investigated, and an improvement in fatigue strength from laser cavitation peening was demonstrated. The impact forces induced by laser ablation and laser cavitation collapse were evaluated with a polyvinylidene fluoride (PVDF) sensor and a submerged shockwave sensor, and the diameter of the laser cavitation was measured by observing a high-speed video taken with a camera. It was revealed that the impact of laser cavitation collapse was larger than that of laser ablation, and the peening effect was closely related to the volume of laser cavitation. Laser cavitation peening improved the fatigue strength of stainless-steel welds.
Highlights
The weld points between metallic material components are the weakest in terms of fatigue properties [1], as welding causes residual tensile stress [2,3,4]
The color of the surface treated by the laser cavitation peening became black due to oxidation caused by LA, and each spot deformed by LA and LC was revealed (Figure 10b)
In order to investigate the effect of laser cavitation LC, which was generated after laser ablation LA, on submerged laser peening, impact and pressure wave were measured by using the handmade polyvinylidene fluoride (PVDF) sensor and the conventional submerged shock wave sensor
Summary
The weld points between metallic material components are the weakest in terms of fatigue properties [1], as welding causes residual tensile stress [2,3,4]. It has been reported that the fatigue strength of the heat-affected zone (HAZ) is higher than that of base metal in some cases; the effect occurs at the microstructure of the HAZ, but causes welding defect and stress concentration [5]. Mechanical surface treatment such as peening can improve the fatigue properties by introducing compressive residual stress and welding line deformation. Improvement in stainless steel weld fatigue strength using a water jet peening method has been reported [10]. The second demonstrates the improvement of weld fatigue properties by laser cavitation peening
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