Challenges in Additive Manufacturing of Space Parts: Powder Feedstock Cross-Contamination and Its Impact on End Products

Abstract

This work studies the tensile properties of Ti-6Al-4V samples produced by laser powder bed based Additive Manufacturing (AM), for different build orientations. The results showed high scattering of the yield and tensile strength and low fracture elongation. The subsequent fractographic investigation revealed the presence of tungsten particles on the fracture surface. Hence, its detection and impact on tensile properties of AM Ti-6Al-4V were investigated. X-ray Computed Tomography (X-ray CT) scanning indicated that these inclusions were evenly distributed throughout the samples, however the inclusions area was shown to be larger in the load-bearing plane for the vertical specimens. A microstructural study proved that the mostly spherical tungsten particles were embedded in the fully martensitic Ti-6Al-4V AM material. The particle size distribution, the flowability and the morphology of the powder feedstock were investigated and appeared to be in line with observations from other studies. X-ray CT scanning of the powder however made the high density particles visible, where various techniques, commonly used in the certification of powder feedstock, failed to detect the contaminant. As the detection of cross contamination in the powder feedstock proves to be challenging, the use of only one type of powder per AM equipment is recommended for critical applications such as Space parts.

A comparison of fatigue strength sensitivity to defects for materials manufactured by AM or traditional processes

“…The importance of stress relieving is highlighted by the results in [30][31][32] for SLM: a non-heat-treated specimen exhibited very high fatigue properties, even with respect to castings, just by pre-heating the powder to 200°C.…”

“…Among the analyzed documents, [6,8,[28][29][30][31][32] report the fatigue limit of the specimens produced by SLM and consider different laser speeds, platform temperatures and specimen orientations with respect to the building direction. On some of the samples, a T6 heat treatment or HIP process was also performed.…”

“…Figure 7: Influence AB condition on the fatigue limit: (a) modelization of subsurface porosity as an equivalent surface crack; (b) reduction in the fatigue limit considering internal defects and equivalent surface defects from AB components (El-Haddad line calibrated on the data point reported in [30]). …”

“…A series of HCF tests [30] on horizontal and vertical samples have been used to estimate the Kitagawa diagram at R=-1 (shown schematically in Fig. 7b).…”

Quality by Design for industry translation: Three‐dimensional risk assessment failure mode, effects, and criticality analysis for additively manufactured patient‐specific implants

“…Changes to these factors can have detrimental effect on powder quality. For example, powder titanium alloys such as Ti6Al4V can easily absorb water, oxygen, and hydrogen from the surrounding atmosphere thereby affecting the density and flow rate of the powder particles, resulting in negative effects in the chemical composition and mechanical properties of the final product . Moreover, the high acquisition cost of powder materials for medical applications makes the handling and recycling of powders key factors in governing their affordability .…”