Microstructure and Micro-mechanical Properties of Cu Based Amorphous Composites with Shape-Memory Crystals

Tapered Cu50Zr42Al8 alloy with good glass-forming ability was fabricated by copper mould suction casting. Cubic AlCu2Zr and B2-ZrCu, thermal-induced martensitic B19'-ZrCu phases form on the glass matrix along the radial direction structure. Size effects on micro-mechanical properties and a unique crack healing behavior were studied. Micro-hardness of monolithic bulk metallic glass (BMG) displays “smaller is softer” trend, that is, the softer surface and the harder center. Whereas the lager size composites possess a softer center and a harder surface, due to the integrative action of the secondary phases. Amorphous matrix is toughened by TRIP (transition induced plasticity) effect of shape-memory phase as well as weakened and embrittled by AlCu2Zr crystal. After annealing, self-healing of Vickers indentation crack occurs as the thermoelastic transformation of shape-memory crystals. As loading, stress-induced martensites transform from B2 to B19', along with volume expansion. Annealed upon the reverse transformation temperature, B19' to B2 transform accompanied by a volume shrinkage, and a restoring force from the structure stress is set up to drive the crack closure.