۱٫ Introduction

۲٫ Experimental approach

۳٫ Results and discussions

۴٫ Conclusions

۵٫ Acknowledgement

۶٫ References

Due to complex microstructure and defect inherited from this ALM process, it is necessary to assess the fatigue resistance of the material constitutive of manufactured parts prior to certification. This work is precisely tackling this issue with a special attention paid to the role of microstructural parameters and defects on fatigue life. Specimens were built with two configurations (0° and 90°) in order to evaluate the impact of the induced anisotropy of microstructure on fatigue properties. X-Ray 3D tomography was used to characterize defect population by their size. Microstructure is furthermore characterized by considering four characteristic scales [1-3]: melt-pools, crystallographic grains, dendritic structure and the precipitates. The fatigue properties are determined by establishing S-N curves for as-built and heat-treated samples for R= -1. The defect size responsible for the fatigue damage initiation is determined in each sample so as to establish a relation between the fatigue limit and the defect size by means of Kitagawa type diagrams. It is shown that the defect size is the first order parameter in terms of the fatigue resistance. Through the Kitagawa diagrams for as-built and heat treated samples, we quantify the improvement of the fatigue resistance due to the peak hardening treatment.

Introduction

Additive manufacture is considered to be a process that breaks with the existing ones, insofar as it offers, in particular, the possibility of producing parts with complex geometry and topographically optimized. In the aeronautical context, the realization of the parts involves them qualification which means the understanding of the fatigue behavior due to integrity of the material. So, the knowledge of the microstructure of the material so as the metallurgical defects inherited to the manufacturing process is therefore necessary in order to quantify the impact of each material parameter on the fatigue behavior of such parts. Thus it will be possible to tend towards the optimization of the process regarding the fatigue behavior. In this work, we are talking about a hypo eutectic aluminum alloy developed by the ALM process. Some studies have been carried out on the microstructural characterization and defects, as well as the anisotropy effects due to the direction of growth of the specimens in relation to the statics mechanical properties such as UTS, Ys and Ef [3, 4]. Concerning the fatigue, Brandl et al [5] showed that anisotropy due direction of production is observable for the platform temperature of 30 ° C. According to the previous author by coupling a platform temperature of 300°C and a T6 heat treatment, no difference is visible anymore due to the direction of sample growth. Maskery et al [6] evaluated the impact of T6 treatment on fatigue performance for as built manufacturing surfaces; they work showed a significant increase in the fatigue limit due to T6 treatment. According to Aboulkhair et al [7], the specimens machined from the T6 heat treated bars have a greater fatigue resistance. Few studies quantify the impact of defects on the fatigue limit.