The terms ‘strength’ and ‘toughness’ are often used interchangeably in everyday life, but in terms of materials, they relate to specific properties. Glass, for example, is strong — scratch-resistant and difficult to permanently bend out of shape — but brittle. Metals, on the other hand, are tough or difficult to shatter — but are generally malleable. Development of a material with both strength and toughness has remained a challenge.
Marios Demetriou, Caltech, USA, and colleagues have developed an alloy of palladium and silver that has a fracture toughness comparable to those of the toughest materials known. The alloy demonstrated the unusual capacity for shielding an opening crack through extensive shear-band sliding processes: The high number of bands in the new alloy formed networks which clustered around the crack tips, blocking them from growing.
Due to the high cost of palladium, the material will be suitable for dental and medical implants. A cheaper version based on copper, iron or aluminium, is being developed for large-scale engineering applications.