Fatigue performance of additive manufactured metallic parts

Abstract

Purpose -Additive manufacturing technologies such as, for example, selective laser melting (SLM) offer new design possibilities for a wide range of applications and industrial sectors. Whereas many results have been published regarding material options and their static mechanical properties, the knowledge about their dynamic mechanical behaviour is still low. The purpose of this paper is to deal with the measurement of the dynamic mechanical properties of two types of stainless steels. Design/methodology/approach -Specimens for dynamic testing were produced in a vertical orientation using SLM. The specimens were turned to the required end geometry and some of them were polished in order to minimise surface effects. Additionally, some samples were produced in the end geometry ("near net shape") to investigate the effect of the comparably rough surface quality on the lifetime. The samples were tension-tested and the results were compared to similar conventional materials. Findings -The SLM-fabricated stainless steels show tensile and fatigue behaviour comparable to conventionally processed materials. For SS316L the fatigue life is 25 per cent lower than conventional material, but lifetimes at higher stress amplitudes are similar. For 15-5PH the endurance limit is 20 per cent lower than conventional material. Lifetimes at higher stress also are significantly lower for this material although the surface conditions were different for the two tests. The influence of surface quality was investigated for 316L. Polishing produced an improvement in fatigue life but lifetime behaviour at higher stress amplitudes was not significantly different compared to the behaviour of the as-fabricated material. Originality/value -In order to widen the field of applications for additive manufacturing technologies, the knowledge about the materials properties is essential, especially about the dynamic mechanical behaviour. The current study is the only published report of fatigue properties of SLM-fabricated stainless steels.

Low-Cycle Fatigue Behaviour of AISI 18Ni300 Maraging Steel Produced by Selective Laser Melting

“…The percentage of porosity, quantified via the Image J software (version 1.6.0, National Institutes of Health, Bethesda, MD, USA), was about 0.74 ± 0.09%. The modus operandi consisted of analysing contrast images (see Figure 2d) between the pores and the base material, obtained from the optical micrographs, and calculating the areas of each of those regions [9]. …”

Tailoring residual stress profile of Selective Laser Melted parts by Laser Shock Peening

“…316L is a widely used austenitic stainless steel and has an UTS of 760 MPa [44]. The powder that was used was DIAMALLOY 1003 obtained from Sulzer Metco, Switzerland.…”

“…During this phase change, the crystal lattice expands and the accumulated stresses due to the shrinkage are relaxed and inversed to a small negative value (i.e. to a compressive residual stress value) [44].…”

Structural performance of additive manufactured metallic material and cross-sections

“…Tensile coupon tests have been undertaken on PBF 316L stainless steel to investigate anisotropy arising from di↵erent building orientations [22,23,25,26,29], the influence of the laser power [3], powder particle size [25] and building layer thickness [25,29] on the material properties, the fatigue performance [26,36] and residual stresses [33,37].…”

“…Coupon tests have been performed on PH1/15-5PH martensitic stainless steel to study the tensile behaviour in di↵erent build orientations [20] and to examine the fatigue behaviour [20,36]. Research has also been carried 95 out into DED 316L [39], the processing parameters for PBF [40] and DED [41] 304 stainless steel, the anisotropy [26,28] and heat treatment [28,30] of PBF aluminium alloys, the anisotropy [17] and heat treatment [31,32] of PBF titanium alloys, the mechanical properties of DED titanium alloys [42,43], the structural integrity of post-processed bronze-nickel alloys [44] and directionality at di↵ering 100 temperatures of a nickel based superalloy [45].…”