Microstructural evolution, thermal stability and microhardness of the Nb–Ti–Si-based alloy during mechanical alloying

Amorphization of the Nb–20Ti–15Si–5Cr–3Hf–3Al (at %) alloy is realized by mechanical alloying (MA). The amorphous phase formation and microstructural evolution are investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). During ball milling, the phase constituent of the alloy powder exhibits a transition from most supersaturated Nb-based solid solutions (Nbss) and a small amount of amorphous phases (after 20 h of ball milling) to a completely amorphous state (after milling for 40 h), which is accompanied by evolution of the powder morphology from flakes to aggregates and eventually to refined granules. The thermal stability of the milled amorphous powders is studied using differential scanning calorimetry (DSC). With the increase of heating temperature, the distortion energy stored during ball milling is released, followed by a transformation from amorphous phase to Nbss and γ-Nb₅Si₃ phases. In addition, the Vickers microhardness remarkably increases, as a result of the amorphous phase formation in the matrix.