Ultra-high strength Co–Ta–B bulk metallic glasses: Glass formation, thermal stability and crystallization.

Co 61 Ta 6 B 33 , Co 59 Ta 8 B 33 , Co 57 Ta 10 B 33 and Co 53 Ta 10 B 37 bulk metallic glasses (BMGs) exhibit a good combination of the ultra-high fracture strength in the range of about 5.4–6.2 GPa, Vickers hardness of 1459–1653 HV0.2 and plastic strain of 0.3–3.2%, depending on composition. Glass forming-ability and physical properties of Co–Ta–B BMGs are discussed in relationship to the Ta and B content and atomic structure. Crystallization upon isochronal and isothermal annealing is studied using differential scanning calorimetry and X-ray diffraction. A novel crystalline phase with ~Ta 2 Co 15 B 8 or ~TaCo 7 B 4 formula is shown to form upon glass annealing. The incubation time for isothermal crystallization in the supercooled liquid state near T g is supposed to be sufficient for thermoplastic forming of Co–Ta–B BMGs. ga1 • Co–Ta–B BMGs with ultrahigh strength and ductility in compression tests. • High glass transition temperature and large supercooled liquid region. • Incubation time for crystallization sufficient for thermoplastic forming. • Novel boride with ~Ta 2 Co 15 B 8 or ~TaCo 7 B 4 unit formula found. [ABSTRACT FROM AUTHOR]