29th Symposium on Fusion Technology (SOFT 2016)

O2A.3 Grain size influence on the response of SPS tungsten to ELM-like thermal shock loading

6 Sep 2016, 11:40

20m

Congress Hall 2nd floor (Prague Congress Centre)

Board: 3

Oral I. Materials Technology O2A

Speaker

Jiri Matejicek (Department of Materials Engineering)

Description

Tungsten is the main candidate material for the plasma facing components of future fusion devices. During operation, these components will be subject to severe conditions, involving both steady state and transient heat loads as well as high particle fluxes. These may lead to surface and structure modifications which influence their performance and lifetime. Therefore, it is necessary to study these effects to understand the physical processes and predict the behavior in such extreme environments. At the same time, various novel materials are being developed with the aim of improved properties and lifetime. Among the processing techniques, spark plasma sintering (SPS) is promising thanks to the relatively low temperatures and shorter sintering times compared to traditional powder metallurgy techniques. In this work the influence of tungsten microstructure on its response to combined deuterium plasma and laser loading were studied. Set of tungsten samples with variable grain size was prepared by SPS through variation of the fabrication parameters. These were exposed to steady state deuterium plasma beam and high energy heat pulses (100 laser pulses of 1 ms duration and power density of 0.76 GW/m2) in the PSI-2 device, simulating tokamak operation in the ELMy H-mode. To discern the contribution of these two exposure modes, both sequential and simultaneous loading was performed. A comprehensive post-mortem characterization of the exposed samples was carried out. Due to the exposure, sample surfaces were roughened, as-prepared grains were recovered; in few isolated cases, cracks were formed. Post-irradiation analysis revealed activation of in-grain slip systems within the loaded surfaces. Damage features were found to depend on more fabrication parameters than grain size. For example, cracks apparently initiated on grinding grooves on (purposefully) unpolished surfaces. Depending on the microstructure, the performance of the SPS tungsten was comparable or better than that of a reference tungsten material (“ITER grade”).