Tungsten Sintering Aid Addition through Nickel Atomic Layer Deposition

Tungsten (W) is found in many high temperature and corrosion resistance applications such as in heat shields for solar probes and fuel elements for nuclear thermal propulsion engines. While W is an ideal material to work with for these applications due to its high melting point and ductility, it is very hard to manufacture for the same reasons. Because of these reasons, much research has been devoted to decreasing the energy required to sinter W powder into W parts while maintaining desired properties.

Here, we propose to utilize atomic layer deposition (ALD) to deposit nickel (Ni) nanoparticles onto W to achieve a well dispersed surface coating and a uniform sample. ALD is a vapor-phase deposition process that doses reactants individually to react with surface sites [1]. When creating W parts, W powder is consolidated by mechanically pressing and sintering at high temperatures for hours to achieve a dense part. Small amounts of transition metals can be added to the W powder to reduce this temperature. Ni is a popular sintering aid in literature, usually added through a Ni solution and dried [2]. The solution added method requires manual grinding and reduction under hydrogen gas, which we are able to avoid with ALD. Ni ALD has been demonstrated on other support materials using bis(cyclopentadienyl)nickel and hydrogen as reactants [3]. In this work, we vary the number of ALD cycles and dosing times to get a variety of Ni loadings on W powder. The weight percent loading of the Ni doped W is analyzed through Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). These samples are compared to solution added samples of a similar composition as a basis. These samples are pressed and then solid-state sintered at 1400C. Solid-state sintering is performed to densify the particles below the bulk eutectic temperature. The density of these samples is then analyzed and compared between the addition methods. We demonstrate ALD as a sintering aid addition method for W particles.

References

[1] Alan W. Weimer. J. Nanopart Res 21:9 (2019)

[2] Vivek K. Gupta, Dang-Hyok Yoon, Harry M. Meyer III, Jian Luo. Acta Materialia 55 (2007) 3131-3142

[3] Troy D. Gould, Alia M. Lubers, Brian T. Neltner, Jacob V. Carrier, Alan W. Weimer, John L. Falconer, J. Will Medlin. Journal of Catalysis 303 (2013) 9-15.