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Stress-Based Fatigue Behaviour of Metal Components Produced by Laser Powder Bed Fusion: Influence of Process Conditions and Post Processes

Boek - Dissertatie

Laser Powder Bed Fusion (LPBF) is one of the most popular metal additive manufacturing technologies capable of manufacturing complex and intricate-shaped designs. In order to use LPBF-processed components in functional applications, their long term fatigue behaviour has to be validated. This work investigates the fatigue behaviour of metal parts produced by LPBF. More specifically, the influence of different process conditions such as heat treatments, surface treatments and build orientations, on the fatigue behaviour, is analysed. This study is performed on miniaturised fatigue samples in three materials: 316L stainless steel, 18Ni300 maraging steel and Ti6Al4V. A stress-based constant amplitude fatigue test campaign is performed for each material with different process conditions and related with the fatigue influencing factors. The results show that the surface condition significantly impacts the fatigue behaviour of all the three materials. A fine surface finish through a suitable surface treatment is preferred to achieve the highest fatigue performance. A fine as-built/stress relieved cellular microstructure in 316L, stress relieved basketweave microstructure in Ti6Al4V and age hardening heat treated microstructure in maraging steel result in the highest fatigue performance of the respective materials. The unique microstructure obtained after LPBF, which is significantly different from that of conventionally manufactured materials, can be fine-tuned to exhibit superior fatigue resistance. With appropriate combinations of process conditions, achieving fatigue performance approaching or exceeding that of conventionally manufactured samples is demonstrated in this work. As a next step, the fatigue behaviour observed in miniaturised samples is related with that of an end-use application component. Low pressure steam turbine blades are built by LPBF, subjected to two different combinations of post processes and tested for fatigue properties. The resulting comparative study indicated that accurate capturing of the influencing factors is needed to scale the fatigue results from lab samples to end-use components in the field.
Jaar van publicatie:2021
Toegankelijkheid:Open