Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 150741

150741 - The Bonding of Tungsten-Stainless Steel Functional Graded Material Manufactured Using Laser Power Bed Fusion 

A significant challenge in industries such as the nuclear sector is to create materials that can withstand high temperatures, inhibit oxidation, and offer a balance of material properties at the interfaces between plasma-material and environment-material. Relying solely on one material or alloying system with conflicting material characteristics requirements in composition and topography, this design challenge cannot be met. Using Laser Power Bed Fusion (LPBF), intricate structures having localized material composition with varying properties over changing dimensions, a potential material design solution known as functional graded materials (FGMs) can be produced. However, LPBF, just like many other Additive Manufacturing (AM) methods produces cycles of melting and rapid solidification, as well as significant residual stresses, which contribute to defects and poor manufacturing in refractory metals such as tungsten. Tungsten (W), due to its high melting temperature, high thermal conductivity, high resistance against sputtering etc, is the most promising material for manufacturing plasma-facing components in future nuclear fusion reactors. Obtaining a reliable bond between tungsten and other materials is necessary since the plasma-facing armor has to be joined to structural and cooling system components. Stainless steel (SS) such as 316L like other AISI steel materials offers very high ductility, impact resistance and excellent corrosion resistance making it a good material choice used for the structural component of plasma-facing armor which requires joining between tungsten and steels. Unfortunately, it is very challenging to join tungsten and steel using conventional welding since they differ greatly in terms of physical properties. For example, the melting point of tungsten is largely higher than that of steel. (3422 ^o C  for tungsten and ~1536 ^o C for steels depending on the composition) and the linear expansion coefficient is significantly different (CFE, 4.5 x 10^{− 6 o}C^-1 for tungsten and 12−14 x 10^{− 6 o}C^-1 for steels at room temperature). Other conventional techniques for joining materials with large melting points such as brazing and diffusion bonding fail to meet the requirements for weapon equipment due to too high bonding temperature for brazing leading to serious grain coarsening, high internal stresses and degrading mechanical performance. The presented work seeks to demonstrate how the fabrication of FGM of Tungsten and 316L stainless steel with varying parameters affects the bonding of the two materials, microstructure and mechanical properties at the interlayer and across layers and how these changes are related to the in-situ energy density and thermal profiles. In this study, FGM of Tungsten on 316L Stainless Steel (W-SS) is fabricated using Laser Powder Bed Fusion. Material characterization of the W-SS interface was conducted, including microstructure, element distribution, phase distribution, and microhardness. A regression model based on the hardness of the interlayer was used to predict the strength of the bond. The preliminary results showed a good bonding with keyhole mode of the melt pool at the W-SS interface making the pre-printed SS layers repeatedly remelted, causing the liquid W to flow into the sub-surface of the pre-printed SS through the keyhole cavities realizing the good bonding of the interface. Energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses of the interlayer indicate the presence of W-Ni and W-Fe intermetallic phases. Mechanical properties in terms of microhardness measurement across the interface and predicted strength based on regression model showed a smooth transition and a high bond strength respectively.

Presenting Author: Gabriel Dzukey University of Toledo

Presenting Author Biography: Gabriel Dzukey is currently a PhD student at the University of Toledo. Doing research in Additive Manufacturing in the Integreated Design and Manufacturing (IDM) Lab under the supervision of Dr. Ala Qattawi. He holds Master's Degree in Mechanical Engineering from the Hohai University (China) .

Authors:

Gabriel Dzukey University of Toledo
Anwar Al Gamal University of Toledo
Sara Ranjbareslamloo University of Toledo
Md. Muhiul Islam Muhit University of Toledo
Ala Qattawi University of Toledo