A test artifact for rapid evaluation of material ductility variation in laser powder bed fusion

This work proposes a test artifact design to evaluate the ductility variation of laser powder bed fusion (LPBF) processed materials by measuring the length of cracking specifically designed to occur along a plane in the artifact in the presence of residual stress. The test artifact consists of an inverted L-shaped cantilever structure whose fixed end is anchored to the build plate and the free overhanging beam end is attached to a support structure. By designing the beam/support interface to have a half-V notch, the residual stress generated in the LPBF process can be concentrated to cause cracking to occur along the interface. It is found that the crack lengths measured in test artifacts printed in Inconel 718 using different process parameters have a decaying exponential relationship with elongations measured in tensile testing of notched tensile specimens, having an R-squared value of 0.9365 in the regression. This strong correlation indicates that an increase in crack length in a test artifact means smaller notch ductility in the printed material. To demonstrate its application, the test artifact is used to evaluate the impact of moisture in feedstock powders on the ductility of the printed materials. Our experimental result shows that the test artifacts printed using dry powders consistently have shorter cracks and hence higher ductility than those printed using powders with 70 % humidity for a wide range of process parameters. This work demonstrates the potential of using the proposed test artifact to evaluate the print quality of an LPBF build in an efficient and cost-effective way.