Microstructure and mechanical properties of the NiNbZrTiAl amorphous alloys with 10 and 25 at.% Nb content.

The results of investigation of two different Ni-based glasses with compositions Ni(58)Nb(10)Zr(13)Ti(12)Al(7) and Ni(58)Nb(25)Zr(8)Ti(6)Al(3) are presented. The structure of the melt spun ribbons was amorphous. The supercooled liquid range decreased and primary crystallization temperature increased with increasing Nb content while the parameter T(g)/T(m) slightly increased. The crystallization process proceeded in a different way. The ribbon containing 10 at.% Nb showed typical primary crystallization of the 50 nm grains of the NiTi(Nb) cubic phase; the ribbon containing 25 at.% of Nb revealed high thermal stability of the amorphous phase, which crystallized only in a small amount in the range of primary crystallization, preserving large fraction of the amorphous phase even high above the end of the crystallization. The tensile load-displacement curves were also different. In both cases, the ribbons revealed quite a large range of the plastic elongation. The ribbon containing 10% Nb showed stress relaxation and was maximally elongated up to 0.6. The ribbon with 25 at.% Nb revealed a hardening effect and the slightly smaller maximal elongation following it. The microstructure of the deformed specimens showed deformation bands parallel to the tensile axis, microcracks formation along shear bands and river-like pattern at the fracture surfaces. In both cases, high resolution electron microscope did not reveal any crystallization after deformation.

The structure and mechanical properties of amorphous and nanocrystalline Fe-Si-B alloys.

This article describes the results of investigations of the microstructure of failure surfaces and the mechanism of deformation of an amorphous Fe(80)Si(11)B(9) alloy, nanocrystallized with the use of Nd:YAG pulsed laser heating. The research included 'in situ' tensile testing in a scanning electron microscope. Mechanical properties were also measured on an Instron-type machine for the amorphous and nanocrystalline alloys. The mechanical tensile tests performed on the amorphous and nanocrystalline samples showed a ductile fracture surface with very high fracture stress. Detailed observations of the flow deformation and fractures revealed the relationship between the quenched-in crystalline and mechanical behaviour.