Shear-induced amorphization of pure niobium during nano-cutting

Abstract The amorphization of pure metallic materials remains one of the key unresolved challenges in materials science. In this study, we investigate the amorphization mechanism in a typical pure metal with body-centred cubic (BCC) lattice—niobium (Nb)—under nano-cutting conditions. A sharp single-crystal diamond tool was used to perform the nano-cutting process. Pre-machining microstructural analysis revealed that the niobium exhibited a coarse-grained structure, with grain sizes exceeding 10 µm. Post-processing, a gradient microstructure was observed, featuring grain sizes in the order of hundreds of nanometres. Significantly, amorphous cluster structures were identified both within the bulk and on the surface of the processed material, with the amorphous fraction of niobium atoms estimated at approximately 0.25% and 0.31%, respectively. To elucidate the underlying deformation and amorphization mechanisms, molecular dynamics (MD) simulations were carried out. Theoretical results demonstrate that the nano-cutting process generates extremely high shear strain, predominantly inducing plastic deformation along the close-packed {110} crystal planes. This shear-dominated deformation ultimately leads to the formation of amorphous regions in pure niobium. Our findings present a novel experimental and computational approach to understanding shear-induced amorphization in monometallic systems, providing new insights into the structural evolution and deformation pathways of BCC metals under extreme mechanical loading.