Role of niobium and oxygen concentration on glass forming ability and crystallization behavior of Zr-Ni-Al-Cu-Nb bulk metallic glasses with low copper concentration

• Low Cu content (Zr56Ni20Al15Cu5)100 − xNbx BMGs were fabricated using suction casting.
• A high glass forming range was determined between 2 and 4 at.% Nb.
• Crystallization pathways upon heating amorphous samples were identified.
• Comparison of non-isothermal activation models was conducted.

Arc melting and suction casting was used to prepare (Zr57Ni20Al15Cu8)100 − xNbx bulk metallic glass alloys with Nb concentration ranging from 1.9 to 4.3 at.%. The glass forming ability and crystallization behavior of these alloys were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). By varying the Nb concentration, a high glass forming range between 2 and 4 at.% Nb was observed in XRD and SEM. It was also revealed that oxygen has a detrimental effect on the GFA within this high glass forming range and the severity was closely linked to the state in which oxygen was present. Since thermal activation is an intrinsic property of crystallization, the activation energy for crystallization was computed from Kissinger, Ozawa and Cheng's methods based on non-isothermal DSC data. A comparison of activation energy models revealed that Kissinger and Ozawa show similar trends while Cheng's method depicted varied results for samples containing pre-existing crystals. For amorphous samples, Kissinger and Ozawa showed the highest value of activation energy (316 kJ/mol and 329 kJ/mol, respectively) at 2.7 at.% Nb, which is consistent with the supercooled liquid region and resulting in higher glass forming ability at this composition.