The role of process-induced materials characteristics on fatigue reliability of selective laser melted Al- and Ti-alloys
Jochen Tenkamp, Institute for Design and Materials Testing (IKW), Department of Materials Test Engineering (WPT)/ TU Dortmund University, Dortmund, GermanyShafaqat Siddique, Institute for Design and Materials Testing (IKW), Department of Materials Test Engineering (WPT)/ TU Dortmund University, Dortmund, GermanyFrank Walther, Institute for Design and Materials Testing (IKW), Department of Materials Test Engineering (WPT)/ TU Dortmund University, Dortmund, GermanyEric Wycisk, Laser Zentrum Nord (LZN), Hamburg, GermanyClaus Emmelmann, Laser Zentrum Nord (LZN), Hamburg, Germany
Due to additive manufacturing and its special process conditions (small melt pool, high cooling rates), new materials characteristics evolve compared to conventional manufacturing, like forming or cutting. This study investigates the fatigue properties of AlSi12 and Ti–6Al–4V structures processed by selective laser melting (SLM). Different processing parameters of the SLM process together with post heat-treatment and mechanical-processing have been investigated to achieve parameters for optimized fatigue performance.
Differences in fatigue properties have been correlated to the microstructural and surface modifications. For AlSi12, the influence of laser energy density, base plate heating and the post-build heat treatment as well as stress relief was investigated. Due to change in porosity and dendritic width, the parameter settings show a significant influence on the high cycle (HCF) as well as on very high cycle fatigue (VHCF) properties until 109 – 1010 cycles. The fatigue life scatter could be reduced from 52 % to 15 % and VHCF strength increased by 47 % using optimized parameter settings. For Ti-6Al-4V, the influence of surface-processing (polishing, shot-peening) and hot isostatic pressing (HIP) were investigated.
As polishing and shot-peening has a significant influence on the roughness, surface hardness and residual stresses, the HCF strength could be improved due to polishing (+125 %) and shot-peening (+107 %). By reducing the porosity with HIP treatment, the HCF and VHCF strength of polished specimen could be further increased by more than 30 % (HCF) and 116 % (VHCF). The results prove that fatigue reliability can be reached by optimized SLM process parameters and adapted post-processing strategies.