The present work concerns the influence of surface (machined, as-built) on the fatigue resistance of AlSi10Mg produced by a powder-bed laser process. The competition between defects and surface roughness is assessed by using Kitagawa-type diagrams. Samples are printed along three directions: 0°, 45° and 90°. After axial fatigue tests with a load ratio of R = −1, all the fracture surfaces are carefully analysed. The initiation sites can be (i) a defect, (ii) the surface roughness, (iii) the surface ripple. The results indicate that ground surfaces lead to the same fatigue life as as-built surfaces. It is also shown that T6 treatment improves the fatigue resistance. However, when specimen surfaces are as-built or ground, it is difficult to correlate the fatigue results with ‘isolated defect size analysis’ neither roughness parameter for an as-built surface. Therefore, microstructure, residual stresses or multiple initiation should be further analysed to understand the results.

The potential of ultrasonic surface mechanical attrition treatment (SMAT) at different temperatures (including cryogenic) for improving the fatigue performance of 304L austenitic stainless steel is evaluated along with the effect of the fatigue loading conditions. Processing parameters such as the vibration amplitude, the size, and the material of the shot medias were fixed. Treatments of 20 min at room temperature and cryogenic temperature were compared to the untreated material by performing rotating–bending fatigue tests at 10 Hz. The fatigue limit was increased by approximately 30% for both peening temperatures. Meanwhile, samples treated for 60 min at room temperature were compared to the initial state in uniaxial fatigue tests performed at R = −1 (fully reversed tension–compression) at 10 Hz, and the fatigue limit enhancement was approximately 20%. In addition, the temperature measurements done during the tests revealed a negligible self-heating (∆t < 50 °C) of the run-out specimens, whereas, at high stress amplitudes, temperature changes as high as 300 °C were measured. SMAT was able to increase the stress range for which no significant local self-heating was reported on the surface.

The design of metallic cast parts requires a compromise between the fatigue resistance of the component and the allowable defect size due to the process. Treatment of defect sensitivity coupled with intrinsic length scales of grains or other microstructure attributes is ultimately necessary to form a predictive basis for defect size effects in forming and growing small defect cracks. This work presents experimental results on high cycle fatigue behavior of specimens containing a surface hemispherical defect under uniaxial tension loading for a wide range of notch size to grain size ratios, including cases where the notch size is on the order of, or even smaller, than the grain size. The influence of grain size on the fatigue strength is clearly demonstrated and the corresponding effects are evaluated. This paper shows that for the same specimen geometry, loading conditions and defect morphology, the fatigue limit is directly dependent on the relationship between the defect size and the grain size. Dimensionless Kitagawa diagram shows that the defect size which impacts the fatigue limit is greater than 0.7 times the grain size in the Armco iron and greater than three times the grain size in other steels.