Achieving Ultralow Wear with Stable Nanocrystalline Metals

Abstract

Recent work suggests that thermally stable nanocrystallinity in metals is achievable in several binary alloys by modifying grain boundary energies via solute segregation. The remarkable thermal stability of these alloys has been demonstrated in recent reports, with many alloys exhibiting negligible grain growth during prolonged exposure to near-melting temperatures. Pt-Au, a proposed stable alloy consisting of two noble metals, is shown to exhibit extraordinary resistance to wear. Ultralow wear rates, less than a monolayer of material removed per sliding pass, are measured for Pt-Au thin films at a maximum Hertz contact stress of up to 1.1 GPa. This is the first instance of an all-metallic material exhibiting a specific wear rate on the order of 10 mm N m , comparable to diamond-like carbon (DLC) and sapphire. Remarkably, the wear rate of sapphire and silicon nitride probes used in wear experiments are either higher or comparable to that of the Pt-Au alloy, despite the substantially higher hardness of the ceramic probe materials. High-resolution microscopy shows negligible surface microstructural evolution in the wear tracks after 100k sliding passes. Mitigation of fatigue-driven delamination enables a transition to wear by atomic attrition, a regime previously limited to highly wear-resistant materials such as DLC.

Solids Under Extreme Shear: Friction‐Mediated Subsurface Structural Transformations

“…Briefly and focusing on microstructure research under a tribological loading, one can either start with an annealed, large-grained bulk or a nanograined material. [35] This structure also shows very low wear rates. An (ultra-) fine-crystalline tribolayer is formed near the surface and often a layered microstructure evolves.…”

“…With the large grained samples, the frictional load modifies the material as sketched above. [35] With more traditional engineering materials, microstructure evolution and changes in wear properties under a tribological load have been investigated for various initial grain sizes; this includes copper, [17,29,36] steels [37] and cobaltbased alloys. [17,[29][30][31] Starting with a nanocrystalline sample, usually leads to grain growth.…”

Adhesive wear mechanisms in the presence of weak interfaces: Insights from an amorphous model system

“…Indeed, some early work on macroscopic junction models supports the latter hypothesis [27][28][29], but is based on macroscale friction at the interface, which is not applicable on the relevant atomistic scales at junctions. Furthermore, the possibility of wear by atom-by-atom attrition has been found in some ultralow wear conditions [30][31][32][33][34][35]. It seems reasonable to assume that this process occurs when both wear particle formation and severe plastic deformation of the surface are suppressed and the surfaces just slip past each other, but this cannot be explained by the theory described above, since any adhesive contact in this framework either leads to wear particle formation or non-negligible plasticity.…”

Attractive In Situ Self‐Reconstructed Hierarchical Gradient Structure of Metallic Glass for High Efficiency and Remarkable Stability in Catalytic Performance

“…In addition, several other compelling properties, e.g., their metastable nature, high Gibbs free energy, easily manipulated atomic compositions, etc., have attracted significant attention in the metallic materials research field. Largely because of their unique structural and thermodynamic peculiarities, the MGs have exhibited many advanced structural and functional properties since their discovery, such as high strength, superior elasticity, excellent corrosion resistance, stable wear resistance, unique soft magnetic properties, etc. However, due to their remaining mysterious intrinsic properties of atomic arrangement, structural dynamic heterogeneity, relaxation, and aging, their current large‐scale industrialized application has only been focused on manufacturing large‐transformer units (soft magnetic property) and a few structural components such as golf drivers (elasticity and strength).…”