Boundaries transformed in pure metals

The situation was less clear for pure metals: indirect evidence7,8 hinted that phase transformations are possible at grain boundaries in pure tin and copper, but no direct observations had been made. [...]if one could produce grain-boundary polymorphs in aluminium that efficiently block dislocation glide (to maximize mechanical strength) and minimize electron scattering (minimizing electrical resistivity), the resulting metal would be a 'dream material' for making wire conductors in overhead power lines - eliminating the need for more-expensive aluminium-based composite wires. [...]a similar concept known as grain-boundary engineering12 - the use of processing methods to obtain grain boundaries that have a desired geometry and properties, without using phase transformations - has so far yielded only modest practical results.