Plastic deformation behavior of Fe–Co–B–Si–Nb–Cr bulk metallic glasses under nanoindentation

• Additional Cr modulation of atomic structure of Fe-Co-B-Si-Nb BMGs.
• An amount of free volume characterized by a combination of nanoindentation and AFM.
• Free volume determined by height measurement of AFM after nanoindentation.

In this work, we investigate the effect of Cr addition on thermal properties and indentation behavior of Fe52Co20−xB20Si4Nb4Crx alloys with x = 0, 1, 3 and 5 at.%, respectively. Among all studied alloys, the Fe52Co17B20Si4Nb4Cr3 bulk metallic glass (BMG) exhibits the highest thermal stability with large supercooled liquid region of 40 K and the pronounced plastic deformation features which is serrated flow (pop-in event) and significant pile-up of materials around indents. This demonstrates that the appropriate addition of Cr in Fe-based BMG can induce the internal atomic structure modulation and promote the mechanical softening, which are discussed in terms of free volume concept.