Abstract
Additive-manufactured metals have a low fatigue limit due to the defects formed during the manufacturing process. Surface defects, in particular, considerably degrade the fatigue limit. In order to expand the application range of additive-manufactured metals, it is necessary to improve the fatigue limit and render the surface defects harmless. This study aims to investigate the effect of laser peening (LP) on the fatigue strength of additive-manufactured maraging steel with crack-like surface defects. Semicircular surface slits with depths of 0.2 and 0.6 mm are introduced on the specimen surface, and plane bending-fatigue tests are performed. On LP application, compressive residual stress is introduced from the specimen surface to a depth of 0.7 mm and the fatigue limit increases by 114%. In a specimen with a 0.2 mm deep slit, LP results in a high-fatigue-limit equivalent to that of a smooth specimen. Therefore, a semicircular slit with a depth of 0.2 mm can be rendered harmless by LP in terms of the fatigue limit. The defect size of a 0.2 mm deep semicircular slit is greater than that of the largest defect induced by additive manufacturing (AM). Thus, the LP process can contribute to improving the reliability of additive-manufactured metals. Compressive residual stress is the dominant factor in improving fatigue strength and rendering surface defects harmless. Moreover, the trend of the defect size that can be rendered harmless, estimated based on fracture mechanics, is consistent with the experimental results.
Highlights
Received: 6 December 2021As additive manufacturing (AM) technology can produce parts with complex shapes that cannot be realized through conventional machining, it is expected to play an active role in production, from various perspectives
The results indicated that semicircular defects with depths below 0.1 mm and 0.2 mm could be rendered harmless by shot peening (SP) and cavitation peening (CP), respectively [24]
The effects of laser peening (LP) on the fatigue strength and the surface defect size that can be rendered harmless by LP in additive-manufactured maraging steel were investigated
Summary
As additive manufacturing (AM) technology can produce parts with complex shapes that cannot be realized through conventional machining, it is expected to play an active role in production, from various perspectives. It can simplify the manufacturing process, and reduce product weight, lead time, and cost. The two main metal AM technologies are powder bed fusion (PBF) and directed energy deposition (DED). In DED, an energy beam, such as a laser or electron beam, irradiates and melts the base material, or both the base material and the supplied material, to build a modeling object. The surface roughness is inferior to that of PBF, DED has advantages over
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