Cold rolling of amorphous/crystalline Ag73.2Cu17.1Zr9.7 composite

In this work, the effect of cold rolling on structure, microstructure and mechanical properties of rapidly solidified Ag73.2Cu17.1Zr9.7 (at.%) amorphous/crystalline composite, containing 80 wt.% Ag, is studied. The as quenched composite is mainly characterized by small amorphous droplets, rich in Cu and Zr, uniformly dispersed in a Ag-rich f.c.c. matrix, as a consequence of the miscibility gap in the liquid. After cold rolling, no phase transformation is detected, whereas a microstructural refinement of the f.c.c. Ag-rich matrix is observed. No evidence of plastic deformation or fracture of the amorphous droplets embedded in the Ag-rich matrix is visible, suggesting that strain is mainly sustained by the crystalline matrix. Microhardness values of both as quenched and rolled ribbons range around 240 HVN, indicating that no significant strain hardening occurs. Experimental values for hardness are successfully fitted considering Orowan and load bearing models. The additional contribution from Hall-Petch effect in the crystalline matrix brings to an overestimation of the calculated values with respect to the experimental ones. Interparticle free distance is smaller than crystallites size, indicating that a fine dispersion of small hard amorphous droplets inhibits dislocation motion in the matrix more effectively than grain boundaries.