Friction control by tailoring deformation mechanism of interfacial grains in metals

Abstract

Micro-scale stick-slip motion of metals is closely related to interfacial plasticity. However, previous studies about the effect of interfacial plasticity on the stick-slip motion only focused on the role of asperity plasticity while ignored the role of grain size of interfacial grains. This study focuses on the stick-slip motion of coarse-grain (CG), ultrafine grain (UFG), nanograin (NG), and heterogeneous grain structure Ti–6Al–4V alloys. Micro-scale stick-slip motion controlled by tailoring grain size of interfacial grains was discovered for the first time. When interfacial materials are coarse-grains (CGs) and ultrafine grains (UFGs), the friction mode is mixed regime (stick-slip competed). When interfacial material is nanograins, the friction mode shows slip regime (slip dominated). When interfacial material is heterogeneous grain structure, the friction mode displays partial slip regime (stick dominated). Notched micro-cantilever tests show that dislocation slip in CGs contributes to large plasticity and high fracture toughness, and that grain boundary migration in NGs results in limited plasticity and low fracture toughness. The plasticity and fracture toughness affected by deformation mechanism play an important role in micro-scale stick-slip motion. The nature of the stick-slip motion control by tailoring grain size of interfacial grains is that the change of grain size can affect the deformation mechanism. This study may provide a new design strategy of micro-scale stick-slip motion control by tailoring deformation mechanism of interfacial grains in metals.