What is the discovery?
Laser powder bed fusion (LPBF) is an additive manufacturing technique which can be used to “3D print” metal components for engineering applications. In a new paper, a team lead by Aeriel D. Murphy-Leonard from the Ohio State University reports a high-energy x-ray study of 316L stainless steel that was produced by LPBF. The team was able to use x-ray tomography to understand porosity in the manufactured samples, and then observe the effect of these pores on the evolution of damage, texture, and strain when the materials are mechanically deformed. Pores near the surface were observed to initiate larger voids and cracks, playing a significant role in damage evolution. Accumulation of damage at pores reduces ductility in these thin-walled additively-manufactured samples, which is the cause of eventual failure.
Why is it important?
Additive manufacturing (AM) has transformed the production of polymers, ceramics, and metals for applications in science, engineering, and medicine. Despite rapid progress, there are still critical limitations that prevent AM from reaching its full potential. Specifically, the quality and repeatability of parts produced are an ongoing concern. The multiple melting-solidification cycles inherent to LPBF result in porosity, distorted parts, cracking, and delamination. Of these defects, porosity is a particularly critical issue in components that require superior strength and ductility as well as fatigue resistance. In order to produce quality AM parts with desirable mechanical properties, it is necessary to understand the influence of porosity.
Why did this research need CHEXS?
This research made use of several unique features of the FAST beamline at CHEXS, which has a mission to understand and improve materials processing. X-ray computed tomography measurements require the high flux of high energy x-rays which are available at FAST, as well as the suite of in-house detector and computational tools provided to users. Complementary far-field X-ray diffraction measurements allowed the team to quantify crystallographic texture and the distribution of elastic strains as a function of lattice orientation during loading. The tensile loading and the rotation of the sample used the RAMS2 Load Frame, which enables 360° rotation of the specimen without interfering with incoming X-rays during mechanical loading.
How was the work funded?
This work was supported by the Office of Naval Research under award N00014-20-WX00405. Research conducted at the Center for High Energy X-ray Sciences (CHEXS) is supported by the National Science Foundation under award DMR-1829070. The additive manufactured tensile specimens used in this work were printed by Dr. Andrew Birnbaum at the US Naval Research Laboratory.
Reference:
Investigation of porosity, texture, and deformation behavior using high energy X-rays during in-situ tensile loading in additively manufactured 316L stainless steel. Aeriel D. Murphy-Leonard, Darren C. Pagan, Patrick G. Callahan, Zach K. Heinkel, Christopher E. Jasien, and David J. Rowenhorst. Materials Science and Engineering: A, Volume 810 (2021); https://doi.org/10.1016/j.msea.2021.141034