Cyclic deformation and fracture behaviour of additive manufactured maraging steel under variable-amplitude loading

The cyclic deformation and fracture behaviour of 18Ni300 maraging steel produced by laser beam powder bed fusion is studied under variable-amplitude loading. The tests were conducted under fully-reversed straincontrolled conditions with a loading sequence comprising three ascending cycles and three descending cycles repeated sequentially until failure. After the tests, fracture surfaces were examined using height and volume surface topography parameters to characterise the fractographic features. Fracture surfaces were also analysed through scanning electron microscopy to identify the main failure modes. Fatigue life was predicted by using the Smith-Watson-Topper and the Basquin-Coffin-Manson models with the Palmgren-Miner damage rule. The former approach was more accurate leading to mean errors close to zero. The values of the kurtosis parameter obtained from both sides of the fracture surfaces correlated well with the fatigue life. SEM analysis showed a mixed ductile-brittle mode of fracture with a predominance of brittle fracture. Crack initiation occurred from manufacturing defects located at the surface or near-surface.