Experimental measurements of surface damage and residual stresses in micro-engineered plasma facing materials

JOURNAL OF NUCLEAR MATERIALS

卷:486

Article

Rivera, David¹  Wirz, Richard E.¹  Ghoniem, Nasr M.¹ 

[1] Univ Calif Los Angeles, Dept Mech & Aerosp Engn, 420 Westwood Plaza, Los Angeles, CA 90095 USA

关键词: Tungsten;    Thermomechanics;    Plasma transients;    Micro-engineered surfaces;    Residual stress;   

DOI  :  10.1016/j.jnucmat.2016.12.035

来源: Elsevier

【 摘 要 】

The thermomechanical damage and residual stresses in plasma-facing materials operating at high heat flux are experimentally investigated. Materials with micro-surfaces are found to be more resilient, when exposed to cyclic high heat flux generated by an arc-jet plasma. An experimental facility, dedicated to High Energy Flux Testing (HEFTY), is developed for testing cyclic heat flux in excess of 10 MW/m(2). We show that plastic deformation and subsequent fracture of the surface can be controlled by sample cooling. We demonstrate that W surfaces with micro-pillar type surface architecture have significantly reduced residual thermal stresses after plasma exposure, as compared to those with flat surfaces. X-ray diffraction (XRD) spectra of the W-(110) peak reveal that broadening of the Full Width at Half Maximum (FWHM) for micro-engineered samples is substantially smaller than corresponding flat surfaces. Spectral shifts of XRD signals indicate that residual stresses due to plasma exposttre of micro-engineered surfaces build up in the first few cycles of exposure. Subsequent cyclic plasma heat loading is shown to anneal out most of the built-up residual stresses in micro-engineered surfaces. These findings are consistent with relaxation of residual thermal stresses in surfaces with micro-engineered features. The initial residual stress state of highly polished flat W samples is compressive (approximate to -1.3 GPa). After exposure to 50 plasma cycles, the surface stress relaxes to -1.0 GPa. Micro-engineered samples exposed to the same thermal cycling show that the initial residual stress state is compressive at (-250 MPa), and remains largely unchanged after plasma exposure. (C) 2017 Elsevier B.V. All rights reserved.

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