Improving the W Coating Uniformity by a COMSOL Model-Based CVD Parameter Study for Denser Wf/W Composites

Metals, vol. 11, pp. 1089

Abstract

Tungsten (W) has the unique combination of excellent thermal properties, low sputter yield, low hydrogen retention, and acceptable activation. Therefore, W is presently the main candidate for the first wall and armor material for future fusion devices. However, its intrinsic brittleness and its embrittlement during operation bears the risk of a sudden and catastrophic component failure. As a countermeasure, tungsten fiber-reinforced tungsten (Wf/W) composites exhibiting extrinsic toughening are being developed. A possible Wf/W production route is chemical vapor deposition (CVD) by reducing WF6 with H2 on heated W fabrics. The challenge here is that the growing CVD-W can seal gaseous domains leading to strength reducing pores. In previous work, CVD models for Wf/W synthesis were developed with COMSOL Multiphysics and validated experimentally. In the present article, these models were applied to conduct a parameter study to optimize the coating uniformity, the relative density, the WF6 demand, and the process time. A low temperature and a low total pressure increase the process time, but in return lead to very uniform W layers at the micro and macro scales and thus to an optimized relative density of the Wf/W composite. High H2 and low WF6 gas flow rates lead to a slightly shorter process time and an improved coating uniformity as long as WF6 is not depleted, which can be avoided by applying the presented reactor model.

Authors 8

1. Leonard Raumann corresponding Aachen Institute of Mineral Engineering (GHI)

   Forschungszentrum Jülich · RWTH Aachen University

   Affiliation as printed

   Forschungszentrum Jülich GmbH (Partner in the Trilateral Euregio Cluster), Institute for Energy and Climate Research, 52428 Jülich, Germany

   Institute of Mineral Engineering, Rheinisch-Westfälische Technische Hochschule Aachen, 52062 Aachen, Germany

2. J.W. Coenen

   University of Wisconsin–Madison · Forschungszentrum Jülich

   Affiliation as printed

   Department of Engineering Physics, University of Wisconsin—Madison, Madison, WI 53706, USA

   Forschungszentrum Jülich GmbH (Partner in the Trilateral Euregio Cluster), Institute for Energy and Climate Research, 52428 Jülich, Germany

3. J. Riesch

   Max Planck Institute for Plasma Physics

   Affiliation as printed

   Max-Planck-Institute for Plasma Physics, 85748 Bavaria, Germany

4. Y. Mao

   Forschungszentrum Jülich

   Affiliation as printed

   Forschungszentrum Jülich GmbH (Partner in the Trilateral Euregio Cluster), Institute for Energy and Climate Research, 52428 Jülich, Germany

5. Daniel Schwalenberg

   Forschungszentrum Jülich

   Affiliation as printed

   Forschungszentrum Jülich GmbH (Partner in the Trilateral Euregio Cluster), Institute for Energy and Climate Research, 52428 Jülich, Germany

6. H. Gietl

   Oak Ridge National Laboratory

   Affiliation as printed

   Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA

7. Ch. Linsmeier

   Forschungszentrum Jülich

   Affiliation as printed

   Forschungszentrum Jülich GmbH (Partner in the Trilateral Euregio Cluster), Institute for Energy and Climate Research, 52428 Jülich, Germany

8. Olivier Guillon Aachen Institute of Mineral Engineering (GHI)

   Forschungszentrum Jülich · Jülich Aachen Research Alliance · RWTH Aachen University

   Affiliation as printed

   Forschungszentrum Jülich GmbH (Partner in the Trilateral Euregio Cluster), Institute for Energy and Climate Research, 52428 Jülich, Germany

   Institute of Mineral Engineering, Rheinisch-Westfälische Technische Hochschule Aachen, 52062 Aachen, Germany

   JARA-Energy, Jülich Aachen Research Alliance, 52428 Jülich, Germany