Imaging of dynamic processes in materials with a laser-wakefield accelerator

Betatron x rays generated from laser-wakefield accelerators are a promising source for imaging dynamic processes in materials. Here, we present proof-of-concept imaging of microstructural evolution in a hypermonotectic <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>Al</a:mi> </a:math> - <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mi>Bi</c:mi> </c:math> alloy, which consists of liquid <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mi>Bi</e:mi> </e:math> particles in a solid <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mi>Al</g:mi> </g:math> matrix. The images capture the elongation and fragmentation of <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mi>Bi</i:mi> </i:math> particles upon isothermal annealing. Because of the femtosecond time scale of the betatron source, the images are not subject to motion blur, whereas the accessibility of the source allows for studies of long-term processes such as annealing. The high-resolution data reveal that the evolution of <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mi>Bi</k:mi> </k:math> particles is mediated by an interplay of grain-boundary wetting and morphological instability, in stark contrast to an earlier proposal for (inverse) coarsening.