Estimation of Inoculation Effect on Phase Formation and Indentation Hardness Behaviour of Zr47.5Cu45.5Al5Co2 and Zr65Cu15Al10Ni10 Bulk Metallic Glass Matrix Composites

The present study aimed to explain and understand the phenomena of nucleation and growth in these
alloys as a function of percentage of inoculant and cooling rate while later varies with change of point
of observation along wedg. Bulk metallic glass matrix composites have emerged as a new potential
material for structural engineering applications owing to their superior strength, hardness and high
elastic strain limit. However, their behaviour is dubious. They manifest brittleness and inferior ductility
which limit their applications. Various methods have been proposed to overcome this problem. With
the help of energy dispersive X-ray spectroscopy (EDS) detector, it can also generate map of crystal
structure of individual elements which can help identify their nature and microstructural features (e.g.
primary, secondary and tertiary dendrite arm spacing). Out of these, introduction of foreign particles
(inoculants) during solidification has been proposed as the most effective. In this study, an effort has
been made to delimit this drawback. A systematic tale has been presented which explains the
evolution of microstructure in Zr47.5Cu45.5Al5Co2 and Zr65Cu15Al10Ni10 bulk metallic glass matrix
composites with varying percentage of ZrC inoculant as analysed by secondary electron, back scatter
electron imaging of “as cast” unetched samples and indentation microhardness testing. Secondary
electron imaging of indents was also performed which shows development of shear transformation
zones at edges of square of indents. Mostly, no cracking was observed, few cracks bearing Palmqvist
morphology were witnessed in samples containing lower percentage of inoculant. It is also observed
experimentally that inoculation has a certain minimum threshold value (0.5%) till which it shows its
maximum effectivity (increase in toughness) and beyond which a balance, decrease and then
increase in toughness is observed. A support is provided to hypothesis that inoculations remain
successful in promoting phase formation and crystallinity and improving toughness.