Novel 3D Sand Molds for Casting of Corrosion Resistant Nickel-Aluminum-Bronze

Although sand-casting is considered a ubiquitous process, fundamental approach to pouringfilling- feeding-solidification of molten metal has largely remained unchanged for several decades. A novel fundamental research program that will both: (1) support significant advances in current Naval manufacturing technologies, i.e. Sand-casting of critical naval alloys (NAB, HY-130, etc.) and (2) support bridging the gap between the oldest (Sand-casting) and newest (3D Sand-Printing – 3SDP) to develop new manufacturing technologies (3DSP of novel sand molds with embedded sensors to monitor real-time metal velocity and solidification rate). The Navy requires high strength corrosion resistant materials. Section 61-19-02 of the BAA #N00173-19-S-BA01 refers to the need for advanced manufacturing technologies to achieve improved material properties to mitigate stress corrosion cracking. This research program is focused on improving naval manufacturing by an innovative approach to bridge the oldest (i.e., sand-casting) and newest (i.e., 3D Sand-Printing-3DSP) manufacturing technologies. Specifically, critical challenges associated with gas entrapment and trapped oxide biofilms in traditional sand casting of Nickel-Aluminum Bronze (NAB) casting is addressed in this proposed study. NAB is a crucial alloy for the Navy (e.g. propellers) due to attractive strength-to-density ratio and corrosion resistance. However, it is an extremely difficult alloy to cast because of inherent turbulence during mold filling, shrinkage and gas porosity. There is a vast body of evidence in literature that has clearly identified that if the metal velocity at the in-gate exceeds a critical velocity (e.g. 0.5m/s for most ferrous and non-ferrous alloys), resulting casting will have defects, and poor mechanical and corrosion resistance. This study aims to establish a novel approach to leverage 3D mold geometries (i.e., 3DSP) to redesign rigging geometry for NAB sand-castings to drastically reduce casting defects, improve material properties and corrosion resistance. In particular, this study will actively collaborate with Materials Team from NSWCCD (Code 162) throughout the course of this project to gather feedback on research findings, facilitate transfer of knowledge to practice and engage a graduate student intern for demonstration and additional corrosion testing. This original study will: (1) develop mathematical model of 3D sprue geometries that can now be produced via 3DSP, (2) perform computational sand casting simulation, and (3) validate numerical and computational results through a thorough design of experiments in sand casting of NAB alloys. Specifically, reduction in casting defects (via micro-CT, SEM and EDS) will be correlated to mechanical strength (via 3-point flexural tests) and corrosion resistance. In Phase-1, the PI proposes to evaluate a benchmark casting geometry and in Phase-2, the PI proposes to demonstrate casting of representative critical Navy castings through this novel 3D sprue geometries and engage other Navy-centric organizations (PSU's ARL, NFPC, NUWC-Keyport), and DOD certified foundries for transfer of knowledge to applied research and development. Findings from this study can be seamlessly transferred to other marine grade alloys and geometries (e.g. thin walls, low pressure sand casting) of interest to the Navy. In addition, unlike direct powder bed metal manufacturing technologies, 3DSP would enable fabrication of large components (6-8') from a wide range of alloys that have been qualified and certified for sand-casting (over 200 casting alloys vs. 2 powder bed metal alloys via MMPDS