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Fatigue crack propagation along interfaces of AM steel implants

Authors: L.M.S. Santos, J.A.M. Ferreira, C. Capela, A.C. Batista, J. de Jesus

Ref.: 18th International Conference on New Trends in Fatigue and Fracture - NT2F18, Lisbon, Portugal, 17-20 July, 2018 (2018)

Abstract: Additive manufacturing (AM) technologies create complex geometry components using a layer-by-layer method, with increasing in low volume production for specific applications, like medical devices, aeronautical parts and even moulding industry components. Mechanical properties under static loading of AM components are comparable to those of conventionally fabricated parts. However, under cyclic loading, the fatigue strength is mostly driven by the impurities and microstructure of the AM materials, needing significant research work. Current work studied the fatigue crack propagation along interfaces of bi-material specimens, composed by a conventional steel substrate on which it was built by sintering laser the remaining part. The sintering laser parts were manufactured in maraging steel AISI 18Ni300, while the substrates were produced using: the stainless steel AISI 420 and a low strength CK45E. Residual stresses were evaluated by X-Ray diffraction and the fracture surface was observed and analyzed with a Scanning Electron Microscope. Hybrid parts exhibit good adhesion in interface. Laser sintering melting process produced longitudinal tensile residual stresses in near surface regions with the average value about 220 MPa. The substrate material has a negligible effect of on fatigue crack propagation rate and path and on the fatigue crack retardation after single overloads.