A novel pathway for multiscale high-resolution time-resolved residual stress evaluation of laser-welded Eurofer97

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Abstract

The plasma-facing components of future fusion reactors, where the Eurofer97 is the primary structural material, will be assembled by laser-welding techniques. The heterogeneous residual stress induced by welding can interact with the microstructure, resulting in a degradation of mechanical properties and a reduction in joint lifetime. Here, a Xe ⁺ plasma focused ion beam with digital image correlation (PFIB-DIC) and nanoindentation is used to reveal the mechanistic connection between residual stress, microstructure, and microhardness. This study is the first to use the PFIB-DIC to evaluate the time-resolved multiscale residual stress at a length scale of tens of micrometers for laser-welded Eurofer97. A nonequilibrium microscale residual stress is observed, which contributes to the macroscale residual stress. The microhardness is similar for the fusion zone and heat-affected zone (HAZ), although the HAZ exhibits around ~30% tensile residual stress softening. The results provide insight into maintaining structural integrity for this critical engineering challenge.

Abstract

Multiscale, high resolution and time-resolved residual stress is quantified in laser-welded Eurofer97 fusion reactor steel.

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An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments

W.C. Oliver, G.M. Pharr (1992)

The indentation load-displacement behavior of six materials tested with a Berkovich indenter has been carefully documented to establish an improved method for determining hardness and elastic modulus from indentation load-displacement data. The materials included fused silica, soda–lime glass, and single crystals of aluminum, tungsten, quartz, and sapphire. It is shown that the load–displacement curves during unloading in these materials are not linear, even in the initial stages, thereby suggesting that the flat punch approximation used so often in the analysis of unloading data is not entirely adequate. An analysis technique is presented that accounts for the curvature in the unloading data and provides a physically justifiable procedure for determining the depth which should be used in conjunction with the indenter shape function to establish the contact area at peak load. The hardnesses and elastic moduli of the six materials are computed using the analysis procedure and compared with values determined by independent means to assess the accuracy of the method. The results show that with good technique, moduli can be measured to within 5%.