Influence of laser power density, number of passes and coefficient overlap of hardening zones on the level of residual stresses, depth and roughness in titanium alloy samples

The paper presents results of studying the effect of laser shock peeing on the surface layer parameters in the titanium alloy specimens. Shot blasting and hydro-shot peening methods are used in the aircraft engine manufacture and create a favorable residual stress diagram to the depth of 0.2 mm. However, this is not enough to ensure the required level of fatigue strength in parts damaged by foreign objects to the depth of 1 mm. In order to increase the specimens’ durability, the paper considers the laser shock peening method. The study object was a specimen with the 50?40?2 mm dimensions made of the titanium alloy. A solid-state Nd:YAG laser was used in laser shock peening of the specimens. A protective layer was formed by aluminum foil with the thickness of 80 ?m. The paper shows a fundamental possibility of achieving a depth of the residual compressive stresses of more than 1.5 mm during the laser shock peeing, which is higher than with the other machining methods. It is found that at the radiation power density of 0.40…0.86I/Imax, the residual stresses level reaches an asymptote and is not changing significantly. With an increase in the number of passes, the residual compression stresses increase by 10…15 %. The paper notes that after two laser passes, the residual stresses level and the depth of action are higher than after a single pass. The overlapping degree also makes it possible to increase the level and depth of residual stresses, but has a lower effect. The roughness parameter reaches an asymptote Ra = 0.4 mm in the range of radiation power density of 0.3…0.6I/Imax. The paper shows that power density and the number of laser passes are decisive in deformation of the sample. At the radiation power density of up to 0.4I/Imax, deformation sharply increases up to 0.2 mm and then remains unchanged up to 0.8I/Imax.
EDN: KMLEZS, https://elibrary/kmlezs

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