Studying The Strcutural Mechanism Of Glass Forming Ability In CuZr-based Alloys

The investigation on the structural factors affecting the glass formation has being a research hotspot in alloys.Many efforts have been devoted to researching the microstructure of the CuZr binary alloy which has strong glass forming ability(GFA).However,it is still a challenge to find whether there is a correlation between the free volume and the GFA.In addition,in CuZr-based alloys,it is known that the structural changes caused by doping some elements also affect the GFA.However,the underlying mechanism of the enhanced GFA induced by microalloying the element with positive heat of mixing is still not clear.In this thesis,synchrotron radiation techniques combined with simulations and calculations are applied to study the microstructural mechanism affecting GFA in CuZr and CuZrNb binay and ternary alloys.The correlation between the free volume and the GFA in a Cu-Zr alloy system has been investigated by synchrotron-radiation based experiments combined with a series of calculations.A new approach for detecting the free volume information in metallic glasses is developed,based on which we reveal that the size of free volume significantly affect the glass formation.In particular,the Cu64Zr36 composition with the local maximum of GFA possesses the local maximum of size value of free volume.The present work provides insights into the glass formation from free volume aspect,which can be helpful to understanding of both structure and properties in metallic glasses.In addition,microalloying certain element with positive heat of mixing leading to the enhanced GFA in multicomponent alloys,has been investigated by systematic experimental measurements coupled with theoretical calculations.It is found that in the Nb-doped CuZr alloys,strong interaction between Nb and Zr atoms leads to a shortened pair distance.Further more,fraction of the icosahedral-like local structures increases with Nb addition and Nb solutes are apt to be separated with each other.These factors contribute to an increase of the atomic level efficiency to fill space and formation of the short-to-medium range orderings.As a result,the amorphous structure is stabilized and the GFA is enhanced accordingly.This work provides an in-depth understanding of microalloying-induced high GFAs in multicomponent alloys and is helpful for guiding the development of more metallic glasses with high GFAs via microalloying,despite the positive heat of mixing between the constituent elements.