Uncovering the coupled impact of defect morphology and microstructure on the tensile behavior of Ti-6Al-4V fabricated via laser powder bed fusion

The preferred defect domain space for enhanced mechanical properties is a critical unknown in the selective laser melting (SLM) additive manufacturing community. This paper presents a systematic approach to relate mechanical properties and the microstructure in the keyhole and the lack of fusion domains for Ti-6Al-4V parts. SLM laser processing conditions were modified to generate three similar amounts of defects in the keyhole and lack of fusion domains. Material from each processing condition was scanned and quantified using x-ray computed tomography to map the defect size and distribution. Samples containing these resultant defects were compared in monotonic tension testing to determine the preferred defect domain for a given amount of defects. While it is known that high amounts of each type of defect is unfavorable, it is shown here that it is more favorable to be in the keyhole domain-at a similar amount of defects-than in the lack of fusion domain. This is attributed to not only the higher sphericity of the keyhole defects but also to the larger amount of crystallographic texture in the keyhole samples which has not been previously well established. Keyhole samples up to 6% porosity maintain yield and UTS values when compared to the stock samples with only a slight loss in elongation. In all cases, when the defect density increases the elongation is reduced. These findings illustrate the preferred location in the processing window for SLM Ti-6Al-4V parts that will be critical for ensuring optimal part performance.

Automated summary

This paper presents a systematic approach to relate mechanical properties and microstructure in the keyhole and lack of fusion domains for Ti-6Al-4V parts. It is shown that, at a similar amount of defects, it is more favorable to be in the keyhole domain than in the lack of fusion domain, due to higher sphericity and crystallographic texture. This finding is critical in ensuring optimal part performance in SLM Ti-6Al-4V parts.