Nuclear Materials and Energy (Jun 2024)
Artificial thermal shock cracks in WRe – A proof of concept study
Abstract
Thermal shock cracks are frequently observed in environments where extensive thermal cycling at high amplitudes is common. Typical cases for such are first wall materials in proposed fusion reactors and rotating anodes for computed tomography scanners. The formation of these cracks is driven by significant tensile stresses during the cooldown phase, following prior plastic deformation at elevated temperatures.This work proposes an experimental approach, where artificial thermal shock-like structures are generated via femtosecond laser ablation in WRe as a model material. Following a detailed laser parameter study in a W sheet material, patterns were introduced to WRe samples and investigated by different microscopy techniques. Their morphology as well as their response to thermo-cyclic loads was investigated and compared to conventionally induced thermal shock cracks.The introduction of artificial cracks by femtosecond laser ablation that mimic the morphology and behaviour of naturally induced thermal shock cracks is feasible within certain boundaries. Cuts, comparable to thermal shock cracks in width and depth, can be ablated. The cuts show an effect on the surrounding microstructure in line with the thermal shock cracks. Therefore, comparability could be proven concerning morphological and microstructural aspects. The conducted thermo-cyclic fatigue tests revealed an analogous effect on subsequent damage accumulation between the thermal shock cracks induced by thermal loading and artificial laser ablated cuts, proving the comparability under dynamic loading conditions. The extent of the effect is adjustable by tailoring the geometry of the lasered structures.The presented work suggests the possibility of studying the influence of thermal shock cracks on further fatigue mechanisms in exceptionally demanding applications, such as first wall materials or rotating anodes, by practical experimentation. Based on the resulting in-depth understanding of underlying interactions, the lifetime of these components might be prolonged by a deliberate introduction of crack networks or laser-ablated structures.
