Glass forming ability and mechanical properties of the NiZrTiSi amorphous alloys modified with Al, Cu and Nb additions

The composition of the amorphous alloy Ni59Zr20Ti16Si5 was modified with 2–9 at.% additions of Cu, Al and Nb. The ribbons and the bars 2.7 mm in diameter were prepared by melt spinning and injection casting from the alloys of the compositions: Ni56Zr18Ti16Si5Al3Cu2, Ni56Zr18Ti13Al6Si5Cu2, Ni56Zr16Ti12Nb9Al3Cu2Si2 and Ni56Zr16Ti12Nb6Al6Cu2Si2. All ribbons were amorphous up to the resolution of the X-ray diffraction and conventional transmission electron microscopy, however rods were partially crystalline. Increase of Al content lowered and Nb content slightly increased crystallization start temperature Tx and glass transition temperature Tg. The influence of composition changes on the overcooled liquid range ΔT was more complicated. The increase of Nb and decrease of Ti and Zr content led to the remarkable increase of the liquidus temperature Tl. As a result GFA calculated as Tg/Tl was lowered to the values about 0.63 for 6 and 9 at.% Nb addition. The activation energies for primary crystallization in alloy with 6 at.% Al and 6 at.% of Nb, were determined. The changes of tensile test strength and microhardness with Al and Nb additions showed hardening effect caused by Nb additions and increase in fracture strength with increasing Al content.