Thermal stability of mechanically alloyed boride/Ti50Cu18Ni22Al4Sn6 glassy alloy composites

The Ti50Cu18Ni22Al4Sn6 multicomponent alloy was chosen as base alloy due to a complete glass formation under ball milling and a sizable supercooled liquid region, ΔTx = 66 K. The mixtures of prealloyed Ti50Cu18Ni22Al4Sn6 fragments with CrB or TiB2 particles up to 30 vol.% were mechanically milled to fabricate the boride/Ti-based glassy alloy composites. The structural features of the as-milled products were characterized using X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. In the ball-milled composites, the CrB or TiB2 particles with sizes ranging around 10–200 nm are dispersed in the Ti-based glassy alloy matrix. Similar to the Ti50Cu18Ni22Al4Sn6 glassy alloy without any borides, a well-defined glass transition temperature, Tg, and a wide supercooled liquid region, ΔTx, are observed also for the boride-containing composites. Furthermore, the glass transition and thermal stability of supercooled liquid for the matrix alloy in the composites are dependent on the fraction of boride addition. In the case of CrB addition, the ΔTx value of glassy phase matrix was reduced due to a strong fraction dependence of the Tg than that of the Tx, remaining at about 60 K for boride fractions less than 15 vol.%. In contrast, both the Tg and Tx of the TiB2-containing composites were raised with increasing TiB2 fraction up to 30 vol.%, resulting in no significant change for the ΔTx.