Microstructure and micro-mechanical properties of Cu based amorphous composites with shape-memory crystals

Abstract:

Tapered Cu50Zr42Al8 alloy with good glass-forming ability were 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 BMG displays "smaller is softer" trend, that is, the softer surface and harder center. Whereas the lager size composites possess a softer center and harder surface, due to the integrative action of the secondary phases. Amorphous matrix is toughened by TRIP effect of shape-memory phase as well as weakened and embrittled by AlCu2Zr crystal. After annealed, self-heal 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 is set up to drive the crack closure.

Key words:bulk metallic glass composites; shape-memory crystals; micro- mechanical behavior; self-healing