| dc.description.abstract | Development of metallic materials is recently essential for biomedical application. Therefore, Zr-based bulk metallic glasses become favorable due to their attractive properties. Zr-Al-Co BMGs, as low-toxic material, having less possibility to harm the human body compared with other Cu-, Ni-, and Be-containing Zr-based BMGs, however, most of them show the limited ductility. The structural modification through partial crystallization on Zr54Al17Co29 BMG was obtained by isothermal annealing and the correlation with the mechanical and corrosion resistance have been investigated. Zr54Al17Co29 BMG rod with diameter of 2, 3, and 4 mm was successfully fabricated by arc melting and suction casting, afterwards, the amorphous properties were examined by XRD, SEM, and DSC. A single broad peak of XRD pattern, good chemical homogeneity, and the information of Tg, Tx, and ∆Tx (742, 794, and 52 K) were obtained from the analyses, indicating the sample was fully amorphous. By Kissinger plots, activation energies of crystallization for the first and second exothermic peak are determined to be 233 and 253 kJ mol-1. The isothermal annealing was conducted at the temperature within SCL region for different times that was determined by JMA isothermal analysis in order to variate sample crystallinities. TEM analysis reveals that ZrCo2Al crystal phase with size of 10 nm is observed from sample with 40.1% crystallinity. Mechanical properties of as-cast and partially crystallized samples containing 6.6; 14.5; 19.8; 25.5; 31.5; 36.4; and 40.1% crystallinities were studied by hardness and compression test. The results reveal that the hardness slightly increases with increasing the crystallinity, in range 540 ± 5 to 575 ± 5 Hv. However, the results of compression test show a different trend, yield strength and plastic strain are significantly improved when the sample reaches 6.6% crystallinity. Afterwards, the deteriorating effect of excess nanocrystal contents for the sample with higher crystallinity on the plastic strain was observed while yield strength remains constant. The sample containing 6.6% crystallinity shows the remarkable improvement of yield strength and plastic strain (2160 ± 110 MPa and 4.7 ± 0.2%), higher than the as-cast counterparts (2130 ± 75 MPa and 2.2 ± 1.6%). This improvement is attributed to the optimum nanocrystal content to restrict the shear bands propagation accompanied without any free volume reduction effect due to short annealing time. In addition, the fracture surface morphology of the sample with 6.6% crystallinity shows the mixed vein and river-like pattern, indicating strong interaction between shear bands and nanocrystals. Moreover, the as-cast and partially crystallized with 6.6% crystallinity samples show similar corrosion resistance and comparable with the 316 stainless steel by potentiodynamic polarization test. In summary, the Zr54Al17Co29 BMG with 6.6% crystallinity is believed as promising candidate for biomaterial applications. | en_US |