The Effect of Process-Induced Porosity on Fatigue Properties of Ti6Al4V Alloy via High-Power Direct Energy Deposition

Abstract

Titanium alloy is widely used in the aviation sector and has become the most important structural material in aircraft manufacturing. However, manufacturing a large-scale titanium component owns a high buy-to-fly ratio due to its poor machinability and expensive price. Over the last decade, the additive manufacturing (AM) technology has developed rapidly and has become a promising processing method for titanium alloys. In the future, in order to enhance processing efficiency and material utilization, a higher laser energy source is supposed to be applied in AM processes. Nevertheless, porosity within the AM fabricated part is the most important issue that restricts the application of AM technology. In the present work, two bulks with different porosities were fabricated using high-power direct energy deposition (HP-DED), and the high cycle fatigue (HCF) performance of the as-build part was tested and compared. The result shows that a lack of fusion (LOF), spherical pores and un-melted particles are the main porosity defects in the as-build part. The shape, size and location of the defect will have a synthetic effect on HCF performance. In addition, the unstable key-hole during the process will facilitate the formation of a pore, which consequently increases the porosity. Online monitoring and closed-loop feedback systems should be established for enhancing the process stability.