Session: 03-02-02: Advanced Manufacturing

Paper Number: 120672

120672 - Contribution of Build Interrupts in Laser Powder Bed Fusion to the Resistance to Fracture of Ti6al4v 

Recognized for its low buy to fly ratio and capability to produce components with unlimited design complexity, additive manufacturing has the potential to transform the aerospace industry.  Laser Powder Bed Fusion (LPBF) has made the most rapid advances in this industry due to the capability for manufacturing structural components from metals that are recognized as difficult to machine.  However, there are occasional issues that arise in the LPBF build process that are poorly understood and that can cause substantial economic burden. One concern is the effect of build interruptions during the printing process on the metal quality and its reliability. Current practice for most original equipment manufacturers is to reject parts that were subject to a machine interrupt during the build. That choice is based on the limited knowledge of the effects of interrupts on the metal quality and its performance. Hence, the objective of the present investigation was to investigate the effects of a build interrupt in LPBF on the strength and the energy to fracture of Ti6Al4V.  

For evaluating the tensile properties, two builds of specimens following ASTM standard E8 were printed and tested, including a control and an interrupted build. For dynamic fracture, a build of Charpy impact specimens following ASTM standard E23-18 was printed and tested; the control and interrupted Charpy specimens were placed in the same build. The “simulated” interrupts consisted of an 8 hour period of machine dwell. In both build designs, the specimens were populated throughout the build space to assess spatial variations in effects of the interrupt. Several representative specimens were selected from each build and underwent computed tomography (CT) to examine the porosity and/or other build anomalies. 

Based on the experimental results from quasi-static tension it was found that there were no significant differences in mechanical properties between metal from the interrupt and control (un-interrupted) condition. While there was some variation in the mechanical properties in the builds, they were identified to be spatial variations and not associated with the interrupt. Similarly, there was no difference in the energy to fracture of metal from the interrupted and control builds.  Akin to results from quasi-static tension to failure, there was some variation in the energy to fracture responses of the build for both the interrupted and control builds, but these reflected spatial variations in the properties and not related to the interrupt. Finally, the CT analysis showed that there was no significant difference in the porosity of the printed specimens between the interrupted and control builds.

Overall, results of this investigation provide additional understanding of the influence from build interrupts on the quality and performance of metal resulting from LPBF. The results suggest that it may be possible to use metal from interrupted builds in applications of low-criticality. However, this investigation should be considered preliminary as it utilized model interrupts, and not machine interruptions related to errors in the build. Most notably this study did not investigate the effect on fatigue properties, which should be a more sensitive assessment of intrinsic defects. In addition, understanding reliability often needs a large amount of data to show statistical confidence, which should come from many different sources. Hence, further study on this topic is warranted.

Presenting Author: Conall Wisdom University of Washington

Presenting Author Biography: Conall Wisdom is a graduate of Materials Science and Engineering at the University of Washington and is now a Research Associate.